Introduction  导言

Light-weight, flexible organic solar cells (F-OSCs) have applications in wearable and portable devices.^1–5 Owing to the rapid development of non-fullerene small-molecule acceptors (NF-SMAs),^6–9 such as Y-series-based acceptors,¹⁰ and device engineering,¹¹ the power conversion efficiencies (PCEs) of rigid OSCs have drastically increased to 19% for large-scale commercialization.^12–14 However, the PCEs of plastic substrate-based OSCs are significantly lower than those of their rigid counterparts, with only a few reports of PCEs over 18%.^15,16 However, in terms of the mechanical properties, NF-SMAs with a rigid backbone tend to form disconnected crystallites and sharp boundaries in the blended film, resulting in film embrittlement and poor mechanical ductility of the functional layer, with a crack-onset strain (COS) of <5%.^17,18 These limitations hinder the flexibility and applicability of F-OSCs. To date, many strategies for material design, such as (1) the introduction of functional units (e.g., hydrogen bonding and flexible segment),^19–23 (2) the fabrication of single-component^24,25 and polymer materials,^26,27 and multi-strategy (e.g., cross-linkable materials,^28,29 insulating elastomers and highly ductile polymers as additives³⁰) and (3) interface engineering,^31–33 have been applied to regulate the PCE and mechanical stability of F-OSCs. However, these flexible devices have unsatisfactory photovoltaic performance and bending cycles. Moreover, under continuous bending or stretching cycles, irreversible microcracks are formed in the functional layer and adjacent layers are delaminated, which significantly shortens the service life of the devices.³⁴ Therefore, more efforts are required to synergistically improve the PCE and mechanical stability of F-OSCs.
重量轻、柔性有机太阳能电池（F-OSC）可应用于可穿戴和便携式设备。^1-5 由于非富勒烯小分子受体（NF-SMA）的快速发展，^6-9 如基于 Y 系列的受体、¹⁰ 和器件工程¹¹ 使刚性 OSC 的功率转换效率 (PCE) 大幅提高到 19%，从而实现了大规模商业化。^12-14 然而，基于塑料基底的 OSC 的 PCE 明显低于刚性 OSC，只有少数报道称 PCE 超过 18%。^15,16 然而，就机械性能而言，具有刚性骨架的 NF-SMA 往往会在混合薄膜中形成断开的晶粒和尖锐的边界、<5 data-dl-uid="12">^17,18 这些限制阻碍了 F-OSC 的灵活性和适用性。迄今为止，已有许多材料设计策略，例如：（1）引入功能单元（例如：）、氢键和柔性材料。、氢键和柔性段），^19-23 (2) 制造单组分^24、25 和聚合物材料，^26,27 以及多策略（e.g.、可交联材料、^28,29 绝缘弹性体和高延展性聚合物作为添加剂³⁰) 以及 (3) 接口工程、^31-33 已被用于调节 F-OSC 的 PCE 和机械稳定性。然而，这些柔性器件的光电性能和弯曲周期并不令人满意。³⁴ 此外，在连续的弯曲或拉伸循环下，功能层会形成不可逆的微裂缝，相邻层也会脱层，这大大缩短了器件的使用寿命。

The photovoltaic active layer is crucial for the flexibility and efficiency of F-OSCs.^35,36 Cross-linked thermosets can be added as the third component to improve ductility and the frozen nano-morphology of the active layer, which lend long-term stability and excellent flexibility to the F-OSCs.^19,29 However, these polymeric cross-linking materials are almost all linear in structure, making it difficult to make the phase stability of the active layer robust and to enlarge the stretchability of the active layer. In contrast, the cross-linking materials with an interpenetrating polymer network (IPN) can freeze the morphology, and also facilitate the blocking of NF-SMA aggregation and diffusion at various strain energies, obtaining ultra-high ductility and stable morphology.³⁷ However, few IPN materials have been successfully applied to F-OSCs, making the development of IPN materials a huge challenge.^38,39 The ideal cross-network morphology tends to freeze the morphology, which is conducive to limiting the aggregation and diffusion of NF-SMAs under various strain energies and obtaining ultrahigh ductility and a stable morphology. Furthermore, the mechanism of stress energy dissipation (concentration and transfer of energy) and nano-morphology evolution (molecular packing and phase separation) of the active layer under strain is currently unclear.^38,40–42
35,36交联热固性塑料可作为第三种成分添加，以改善活性层的延展性和冻结纳米形态，从而为 F-OSC 提供长期稳定性和出色的灵活性。^19,29 然而，这些高分子交联材料几乎都是线性结构，因此很难使活性层的相稳定性保持稳定，也很难提高活性层的伸展性。³⁷ 相比之下，具有互穿聚合物网络（IPN）的交联材料不仅能冻结形态，还能在各种应变能下促进 NF-SMA 聚集和扩散的阻断，从而获得超高的延展性和稳定的形态。³⁷ 然而，目前成功应用于 F-OSC 的 IPN 材料寥寥无几，这使得 IPN 材料的开发成为一项巨大的挑战。^38,39 理想的交叉网络形态趋于冻结，有利于限制 NF-SMA 在各种应变能下的聚集和扩散，获得超高的延展性和稳定的形态。此外，活性层在应变下的应力能量耗散（能量集中和传递）和纳米形态演变（分子堆积和相分离）机制目前还不清楚。

In addition to the mechanical aspects, high-performance crosslinked thermosets that improve the PCE of F-OSCs have not yet been realized.^43–45 This is attributed to two reasons: (1) the polymerization reaction of typical cross-linked thermoset materials occurs at higher temperatures, which can easily cause expansion or contraction of the plastic substrate, resulting in incompatibility with the OSC manufacturing process.^46–48 Additionally, the additional stress energy created ultimately sacrifices device performance. (2) The curing reaction that affords the crosslinked matrix usually requires an initiator to assist in the polymerization reaction and is induced by intense ultraviolet (UV) radiation.^44,45,49 The initiator is usually strongly oxidizing and will become an impurity in the process of forming the nano-morphology of the active layer, and sacrifice the photovoltaic performance.
43-45这归因于两个原因：(1) 典型交联热固性材料的聚合反应发生在较高温度下，很容易导致塑料基底膨胀或收缩，从而与 OSC 制造工艺不兼容。^46-48 此外，产生的额外应力能量最终会牺牲器件性能。(^44,45,49 引发交联基质的固化反应通常需要引发剂来协助聚合反应，并由强烈的紫外线 (UV) 辐射诱导。

In this study, to improve the stability and deformability of the PM6 : BTP-eC9 active layer, we used a crosslinking monomer, thioctic acid (TA), with dynamic covalent disulfide bonds and H-bonds to fabricate a blend film. The self-healing TA exhibits high activity and low-temperature (60 °C) curing properties. TA was doped in the PM6 : BTP-eC9 active layer as a crosslinking additive such that both the in situ crosslinking and nano-morphology formation processes are simultaneously triggered. In addition, driven by in situ crosslinking, the molecular packing and phase separation of the donor (D)/acceptor (A) and the nano-morphology during film formation, were finely controlled. The mechanical properties (modulus, Tg, stiffness, COS and fracture strain) of the resultant photovoltaic films were studied. The COS_FOW of the optimal TA-doped PM6 : D18-2F : BTP-eC9 film was 76.58% higher than that of the PM6 : BTP-eC9 binary film (3.63%), which was attributed to the dissipation of mechanical stress by the cross-linked network under tensile deformation. Subsequently, the PCEs and the thermal stress tolerance of the fabricated F-OSCs were analyzed. We believe that this study provides a simple yet effective strategy for fabricating flexible organic photovoltaic devices with high PCEs and excellent mechanical stability.
在本研究中，为了提高 PM6 : BTP-eC9 活性层的稳定性和可变形性，我们使用了具有动态共价二硫键和 H 键的交联单体硫辛酸（TA）来制造混合薄膜。自愈合 TA 具有高活性和低温（60 °C）固化特性。在 PM6 : BTP-eC9 活性层中掺入 TA 作为交联添加剂，可同时触发原位交联和纳米形态形成过程。此外，在原位交联的驱动下，供体（D）/受体（A）的分子堆积和相分离以及薄膜形成过程中的纳米形态都得到了精细控制。研究了所得光伏薄膜的机械性能（模量、Tg、硬度、COS 和断裂应变）。最佳 TA 掺杂 PM6 : D18-2F : BTP-eC9 薄膜的 COS_FOW 比 PM6 : BTP-eC9 二元薄膜（3.63%）高出 76.58%，这归因于交联网络在拉伸变形时消散了机械应力。随后，我们分析了所制备 F-OSC 的 PCE 和热应力耐受性。我们相信，这项研究为制造具有高 PCEs 和优异机械稳定性的柔性有机光伏器件提供了一种简单而有效的策略。

Results and discussion  结果和讨论

Materials characterization and in situ cross-linked matrix
材料表征和原位交联基质

A state-of-the-art conjugated polymer donor, PM6, and non-fullerene acceptor, BTP-eC9, were chosen to fabricate the OSCs, whose molecular structure is shown in Fig. 1B and Fig. S2 (ESI†). The synthetic routes to the high-molecular-weight D18-2F are depicted in Scheme S1 (ESI†). The chemical structure of D18-2F was confirmed using nuclear magnetic resonance (NMR) spectroscopy and elemental analysis (Fig. S3–S6, ESI†). Furthermore, theoretical calculations were performed to explore the geometrical conformation, electrostatic potential (ESP), and the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of D18-2F using density functional theory at the B3LYP/6-31G (d,p) level (Fig. S7–S10, ESI†). As shown in Fig. S7 (ESI†), the main molecular-chain exhibited an overall negative ESP, which indicates its excellent electron-donating ability, and an almost planar geometrical conformation in the top view (Fig. S8, ESI†). The energy levels and molecular weight characteristics of D18-2F are shown in Fig. S11 and S12 (ESI†). A cascade energy structure was formed in the PM6 : D18-2F-based device, which facilitates charge transport and yields a high open-circuit voltage (V_OC). In addition, as shown in Fig. S13 and S14 (ESI†), the PM6 (absorption peak at 616 nm) and D18-2F (absorption peak at 532 nm) spectra overlapped and enhanced absorption was exhibited at 500–650 nm. These results were complemented by an increase in the intensity of BTP-eC9 absorption at 700–900 nm (absorption peak at 839 nm).
我们选择了最先进的共轭聚合物给体 PM6 和非富勒烯受体 BTP-eC9 来制造 OSC，其分子结构如 Fig. 1B 和图 S2 (ESI†) 所示。高分子量 D18-2F 的合成路线见方案 S1（ESI†）。D18-2F 的化学结构通过核磁共振 (NMR) 光谱和元素分析得到了证实（图 S3-S6，ESI†）。此外，还利用密度泛函理论在 B3LYP/6-31G (d,p) 水平上对 D18-2F 的几何构象、静电位 (ESP) 以及最高占有分子轨道 (HOMO) 和最低未占有分子轨道 (LUMO) 能级进行了理论计算（图 S7-S10，ESI†）。如图 S7（ESI†）所示，主分子链显示出整体负的 ESP，这表明其具有出色的电子负载能力，并且在俯视图中几乎呈平面几何构象（图 S8，ESI†）。D18-2F 的能级和分子量特征见图 S11 和 S12（ESI†）。在基于 PM6 ：基于 D18-2F 的器件中形成了级联能量结构，从而促进了电荷传输并产生了较高的开路电压（V_OC ）。此外，如图 S13 和 S14（ESI†）所示，PM6（616 纳米处的吸收峰）和 D18-2F （532 纳米处的吸收峰）光谱重叠，在 500-650 纳米处的吸收增强。 此外，BTP-eC9 在 700-900 纳米波长处的吸收强度（839 纳米波长处的吸收峰）也有所增加。

To investigate the effect of the incorporation of D18-2F on the molecular crystallinity and packing behavior of PM6, grazing-incidence wide-angle X-ray scattering (GIWAXS) was performed (Fig. 1C and D), and the crystallographic parameters of the films are summarized in Table S1 (ESI†). Fig. 1E shows the in-plane (IP) and out-of-plane (OOP) one-dimensional (1D) line-cut profiles. The OOP 1D line-cut profile demonstrates that D18-2F has a larger π–π stacking distance (d₍₀₁₀₎ = 3.875 Å) than that of PM6 (3.749 Å) and a face-on oriented packing structure. The PM6 : D18-2F (9 : 1) film displays a strong diffraction peak in the OOP direction at 1.655 Å⁻¹ (d-spacing = 3.796 Å) (Fig. S15 and Table S1, ESI†). The crystallite coherent length (CCL) in the OOP direction of the PM6 : D18-2F (9 : 1) film increased from 19.29 Å in the PM6 film to 21.56 Å. This enhanced crystallization and aggregation is regarded as beneficial to carrier transport. In addition, even after the introduction of crosslinked TA, the donors film maintained its preferred face-on orientation, which facilitates charge transport in the OSC.
为了研究掺入 D18-2F 对 PM6 分子结晶度和堆积行为的影响，进行了掠入射广角 X 射线散射 (GIWAXS) (Fig. 1C and D)，表 S1（ESI†）汇总了薄膜的晶体学参数。图 1E 显示了面内 (IP) 和面外 (OOP) 一维 (1D) 线切割剖面图。OOP 一维线切割剖面图表明，D18-2F 的 π-π 堆垛间距（d₍₀₁₀₎ = 3.875 Å）比 PM6（3.749 Å）大，并且具有面朝上的定向堆积结构。PM6 ：D18-2F (9 : 1) 薄膜在 1.655 Å^-1 (d-spacing = 3.796 Å) 的 OOP 方向上显示出一个强衍射峰（图 S15 和表 S1，ESI† ）。PM6 : D18-2F (9 : 1) 薄膜 OOP 方向上的晶体相干长度 (CCL) 从 PM6 薄膜的 19.29 Å 增加到 21.56 Å。此外，即使在引入交联 TA 后，供体薄膜仍保持其优先的面朝上取向，这有利于 OSC 中的电荷传输。

Based on this efficient photovoltaic material, with the in situ crosslinking strategy in this study, the molecular crystallinity and stacking is finely tuned to optimize the molecular arrangement and phase separation, while simultaneously achieving frozen nanomorphology with superior deformability. To form a highly crosslinked network, the curing temperature of the thermoset precursor must be higher than its melting point. Hence, the melting point of an ideal in situ thermally crosslinked material must be low enough to be suitable for device processing (∼100 °C). For this, we developed a cross-linking monomer TA with dynamic covalent disulfide and H-bonds. Notably, thermally crosslinked materials with O–H bonds exhibit strong H-bonding interactions with photovoltaic materials, which is beneficial for confining the chain relaxation of donor and acceptor materials. Upon heating at 60 °C, TA forms linear poly(TA) through ring-opening polymerization of disulfide bonds (Fig. 1A), which is confirmed by the Fourier-transform infrared (FTIR) spectra (Fig. S16, ESI†). Dynamic bonding facilitates stress dissipation in stretched polymer films through reversible bond cleavage and formation, which is conducive to the formation of an ideal blend film morphology with high ductility.
在这种高效光伏材料的基础上，本研究采用了原位交联策略，对分子结晶度和堆积进行了微调，以优化分子排列和相分离，同时实现了具有优异变形能力的冷冻纳米形态。要形成高度交联的网络，热固性前体的固化温度必须高于其熔点。因此，理想的原位热交联材料的熔点必须足够低，以适合器件加工（∼100 °C）。为此，我们开发了一种具有动态共价二硫键和 H 键的交联单体 TA。值得注意的是，带有 O-H 键的热交联材料与光伏材料之间具有很强的 H 键相互作用，这有利于限制供体和受体材料的链松弛。在 60 °C 下加热时，TA 通过二硫键的开环聚合作用形成线性聚 TA（图 1A），傅立叶变换红外光谱（FTIR）证实了这一点（图 S16，ESI†）。动态键合通过可逆的键合断裂和形成，促进了拉伸聚合物薄膜的应力消散，有利于形成具有高延展性的理想共混薄膜形态。

The 2D ¹H–¹H nuclear magnetic resonance (NMR) was introduced to detect molecular interaction between TA and the host donor in the solution state. Nuclear Overhauser effect spectroscopy (NOESY) NMR spectra can provide information about protons which are 5 Å or less apart in space.^50,51 As shown in Fig. 1F and Fig. S17 and S18 (ESI†), strong correlation signals between the characteristic protons of TA and –CH₂– protons of PM6 were clearly observed in the 2D NOESY spectra of TA-doped PM6 solution relative to that of pristine PM6 (signals marked with a yellow shade). The strong correlation signal between the characteristic protons of TA and the –CH₂– protons of BTP-eC9 can also be clearly observed in the 2D NOESY spectra of TA-doped BTP-eC9 solution (the signals marked with dashed boxes) (Fig. 1G). In addition, as shown in Fig. S19 (ESI†), TA-doped L8-BO solution demonstrates the same results as TA-doped BTP-eC9 solution. These results confirm the existence of intermolecular interactions between TA with PM6 donor and BTP-eC9 acceptor molecules through varying the functional groups.
二维¹H-¹H核磁共振（NMR）被引入检测溶液状态下TA与主供体之间的分子相互作用。核超豪瑟效应光谱（NOESY）核磁共振波谱可提供空间相距 5 Å 或更小的质子的信息^50,51 如 Fig.S17 和 S18（ESI†）所示，在掺杂 TA 的 PM6 溶液的二维 NOESY 图谱中，可以清楚地观察到 TA 的特征质子与 PM6 的 -CH₂- 质子之间相对于原始 PM6 的强相关信号（用黄色阴影标记的信号）。在掺杂了 TA 的 BTP-eC9 溶液的二维 NOESY 图谱中，也可以清楚地观察到 TA 的特征质子与 BTP-eC9 的 -CH₂- 质子之间的强相关信号（虚线框标出的信号）（图 1G）。此外，如图 S19（ESI†）所示，掺杂 TA 的 L8-BO 溶液与掺杂 TA 的 BTP-eC9 溶液显示出相同的结果。这些结果证实了 TA 与 PM6 给体分子和 BTP-eC9 受体分子之间存在着分子间相互作用。

The key to fabricating mechanically robust OSCs lies in the ability to stretch the active layers without experiencing fracture and electrical failure. Therefore, we determined the intrinsic mechanical properties of the PM6 and PM6 : D18-2F (9 : 1 w/w) films (COS, elastic modulus, stiffness, and compliance). Pseudo free-standing tensile tests for films-on-water (FOW) and films-on-elastomer (FOE), as well as peak force quantitation nanomechanical mapping (PFQNM), were used to study the intrinsic flexibility of the pristine donor films (Fig. 1H and Fig. S20, Table S2, ESI†). The COS values obtained using the FOW and FOE methods were named COS_FOW and COS_FOE, respectively. The typical stress–strain curve of the neat donor films was obtained using the FOW method (Fig. 1H). The COS_FOW of the PM6 film was 9.3%, indicating its limited flexibility, whereas the COS_FOW of the PM6 : D18-2F (9 : 1 w/w) film (11.7%) was 25.8% higher than that of the PM6 film. When 3 wt% crosslinked TA was used in the fabrication of the PM6 : D18-2F (9 : 1 w/w) film, the COS_FOW increased by 54%, demonstrating that the crosslinked network effectively dissipated the concentrated mechanical stress in the film. However, the COS_FOE of the PM6 film in a previous study was 17.5%, which is significantly higher than the COS_FOW obtained in this study because the PM6 film was strongly bonded with the elastic substrate.¹⁸ The stress–strain curve of the BTP-eC9 film was not obtained because it was extremely brittle and broke apart during the floating process; notably, a gentle vibration of the water bath shattered this film. In addition, the Derjaguin–Muller–Toporov (DMT) moduli of PM6, D18-2F, and PM6 : D18-2F (9 : 1 w/w) films were determined to be 2.98, 2.26, and 2.69 GPa, respectively, using PFQNM (Fig. S20, ESI†). Moreover, the 3 wt% TA-dropd PM6 : D18-2F film exhibited a higher compliance of 5.51 × 10⁻² m N⁻¹, which suggests its high mechanical stability.
制造机械坚固的 OSC 的关键在于拉伸活性层而不发生断裂和电气故障的能力。因此，我们测定了 PM6 和 PM6 : D18-2F（9 : 1 w/w）薄膜的内在机械特性（COS、弹性模量、刚度和顺应性）。水上薄膜 (FOW) 和弹性体上薄膜 (FOE) 的伪独立拉伸试验以及峰值力定量纳米力学绘图 (PFQNM) 被用来研究原始供体薄膜的内在柔韧性（Fig. 1H 和图 S20，表 S2，ESI† ）。使用 FOW 和 FOE 方法获得的 COS 值分别命名为 COS_FOW 和 COS_FOE 。使用 FOW 方法得到了完整供体薄膜的典型应力-应变曲线（图 1H）。PM6 薄膜的 COS_FOW 为 9.3%，表明其柔韧性有限，而 PM6 ：D18-2F（9：1 w/w）薄膜的 COS_FOW（11.7%）比 PM6 薄膜高 25.8%。当使用 3 wt% 的交联 TA 制造 PM6 ：D18-2F (9 : 1 w/w)薄膜时，COS_FOW增加了54%，表明交联网络有效地消散了薄膜中集中的机械应力。然而，在之前的一项研究中，PM6 薄膜的 COS_FOE 为 17.5%，明显高于本研究获得的 COS_FOW ，这是因为 PM6 薄膜与弹性基底紧密结合。¹⁸ 没有获得 BTP-eC9 薄膜的应力-应变曲线，因为它非常脆，在漂浮过程中破裂；特别是，水浴的轻微振动就会粉碎这种薄膜。此外，PM6、D18-2F 和 PM6 ：使用 PFQNM 测定的 Derjaguin-Muller-Toporov (DMT) 模量分别为 2.98、2.26 和 2.69 GPa（图 S20，ESI†）。此外，3 wt% TA-dropd PM6 ：D18-2F 薄膜的顺应性高达 5.51 × 10^-2 m N^-1 ，这表明它具有很高的机械稳定性。

Molecular packing and crystallization behavior
分子堆积和结晶行为

In non-fullerene small-molecule acceptor (NF-SMA)-based photovoltaic systems, the device performance strongly depends on the evolution of crystallization and the aggregation of NF-SMAs. During the spin-coating and thermal annealing processes, in situ UV-vis absorption was measured to investigate the effect of TA doping on the crystallization and stacking of the BTP-eC9 materials. The pure TA film exhibited no absorption in the 400–1000 nm region (Fig. S21, ESI†). The time evolution contour maps of the UV-vis absorption spectra during the spin-coating process are shown in Fig. 2A and B. The crystallization of the BTP-eC9 acceptor was studied and its crystals were extracted from the solvent and converted into film in three steps (Fig. 2C). In the first step, a short peak of BTP-eC9 was observed at a short wavelength, which is attribute to the removal of excess solvents that would decrease intermolecular distances. In the second step, the peak was red-shifted and increased in intensity, which is attributed to the aggregation of molecules during the transition from a solution to a film state. In the final step, the peak location and intensity remained constant, indicating a steady film state. The absorption of 3 wt% TA-doped BTP-eC9 in the solution state was slightly red-shifted (751.8 nm) compared to that of the undoped sample (749.2 nm), which may be attributed to the aggregation induced by TA (with O–H bonds). In addition, the aggregation of 3 wt% TA-doped BTP-eC9 began earlier than that of BTP-eC9 and exhibited shorter aggregation duration (Fig. 2C). The introduction of TA into PM6 showed a similar aggregation trend (Fig. S22, ESI†).
在基于非富勒烯小分子受体（NF-SMA）的光伏系统中，器件性能在很大程度上取决于结晶的演变和 NF-SMA 的聚集。在旋涂和热退火过程中，测量了原位紫外可见吸收，以研究掺杂TA对BTP-eC9材料结晶和堆积的影响。纯 TA 薄膜在 400-1000 纳米区域没有吸收（图 S21，ESI†）。旋涂过程中紫外-可见吸收光谱的时间演变等值线图见图 2A 和 B。对 BTP-eC9 受体的结晶过程进行了研究，并分三步将其晶体从溶剂中提取出来并转化成薄膜（图 2C）。在第一步中，BTP-eC9 在短波长处出现了一个短峰，这是因为去除了会减小分子间距离的过量溶剂。在第二步中，峰值发生了红移，强度增加，这是因为分子在从溶液状态过渡到薄膜状态的过程中发生了聚集。在最后一步，峰值位置和强度保持不变，表明薄膜状态稳定。与未掺杂样品（749.2 纳米）相比，掺杂了 3 wt% TA 的 BTP-eC9 在溶液状态下的吸收（751.8 纳米）略有红移，这可能是由于 TA 诱导的聚集（带有 O-H 键）。此外，掺杂 3 wt% TA 的 BTP-eC9 比 BTP-eC9 更早开始聚集，并且聚集持续时间更短（图 2C）。在 PM6 中引入 TA 也显示出类似的聚集趋势（图 S22，ESI†）。

In situ UV-vis absorption spectra of the BTP-eC9 and 3 wt% TA-doped BTP-eC9 acceptor films were obtained at 100 °C to further observe their crystallization behavior (Fig. 2D and E). Crystallization was observed for the BTP-eC9 acceptor film during the first 100 s of thermal annealing, which then stabilized, as evidenced by the evolution of the absorption intensity and peak location. In the case of the 3 wt% TA-doped BTP-eC9 film, the absorption intensity increased after thermal annealing, indicating the formation of an in situ crosslinked network. To study the influence of the crosslinked network on the phase domain during thermal annealing, changes in the peak location of the acceptor in the blended film were observed (Fig. 2F). The peak of the BTP-eC9 film was blue-shifted by 6.4 nm, from 823.7 to 817.3 nm. However, after the introduction of TA, the blue shift caused by the thermal motion of the molecules was significantly suppressed. This may be attributed to the in situ crosslinked network that enables the active layer to form a frozen nanomorphology, which is extremely beneficial for both mechanical flexibility and thermal stability.
BTP-eC9 和 3 wt% TA 掺杂的 BTP-eC9 受体薄膜在 100 °C 时的原位紫外可见吸收光谱，以进一步观察它们的结晶行为（ 图 2D 和 E）。在热退火的最初 100 秒内，BTP-eC9 受体薄膜出现了结晶现象，随后结晶趋于稳定，吸收强度和峰值位置的变化证明了这一点。在掺杂 3 wt% TA 的 BTP-eC9 薄膜中，热退火后吸收强度增加，表明形成了原位交联网络。为了研究热退火过程中交联网络对相域的影响，观察了混合薄膜中受体峰位置的变化（图 2F）。BTP-eC9 薄膜的峰值蓝移了 6.4 nm，从 823.7 nm 到 817.3 nm。然而，在引入 TA 后，分子热运动引起的蓝移被显著抑制。这可能是由于原位交联网络使活性层形成了冻结纳米形态，这对机械柔性和热稳定性都极为有利。

GIWAXS was performed to investigate the effect of introducing TA on the molecular crystallinity and packing behavior. The 2D diffraction patterns of BTP-eC9 and PM6 films with and without TA are shown in Fig. 2G and Fig. S23, S24 (ESI†), respectively. The OOP 1D line-cut profile (Fig. 2G) demonstrates that the 3 wt% TA-doped BTP-eC9 film has a tighter packing with a smaller stacking distance (d₍₀₁₀₎ = 3.59 Å) than that of BTP-eC9 (3.72 Å). In addition, the CCL of the OOP π–π stacking and the IP lamellar stacking also increased from 18.39 and 39.13 to 20.06 and 43.56 Å, respectively, which is beneficial for carrier transport. The TA crosslinker with O–H bonds also optimized the crystallization and packing of the PM6 donor (Fig. S24, ESI†) due to its dynamic covalent disulfide bonds and H-bonds, which enhanced the balance efficiency and mechanical stretchability of the active layer.
为了研究引入 TA 对分子结晶度和堆积行为的影响，进行了 GIWAXS。含 TA 和不含 TA 的 BTP-eC9 和 PM6 薄膜的二维衍射图样分别见图 2G 和图 S23、S24（ESI†）。OOP 1D 线切割剖面图（Fig. 2G）表明，掺杂 3 wt% TA 的 BTP-eC9 薄膜具有更紧密的堆积，堆积距离（d₍₀₁₀₎ = 3.59 Å）比 BTP-eC9 薄膜（3.72 Å）更小。此外，OOP π-π 堆积和 IP 片层堆积的 CCL 也分别从 18.39 Å 和 39.13 Å 增加到 20.06 Å 和 43.56 Å，有利于载流子的传输。具有 O-H 键的 TA 交联剂还优化了 PM6 供体的结晶和堆积（图 S24，ESI† ），这是因为其动态共价二硫键和 H 键提高了活性层的平衡效率和机械伸展性。

Photovoltaic properties of rigid and flexible devices
刚性和柔性设备的光伏特性

Photovoltaic performance was assessed by fabricating rigid devices comprising glass/ITO/4PADCB/active layer/PNINN/Ag. The fabrication procedure is described in the ESI.† The current density–voltage (J–V) characteristics were obtained under AM 1.5G simulated 1 sun solar illumination (Fig. 3A and Fig. S25, ESI†), and the relevant photovoltaic parameters are summarized in Table 1 and Fig. S3–S5 (ESI†). Due to its superior transmittance and high work function, the self-assembled monolayer of 4PADCB was used in place of the typical PEDOT:PSS (4083) hole transport layer. The 4PADCB-based PM6 : BTP-eC9 binary device exhibited an improved PCE of 18.97%. The optimal ternary device exhibited substantially higher values of PCE (19.84%), V_OC of 0.863 V, short-circuit current density (J_SC) of 28.97 mA cm⁻², and fill factor (FF) of 79.4%, which are the highest reported values to date. These values could be attributed to the incorporation of 3 wt% TA and 10 wt% D18-2F as the guest acceptor. The device parameters for other ratios of the TA and D18-2F are presented in Fig. S26 and S27 (ESI†), with the corresponding photovoltaic parameters summarized in Tables S4 and S5 (ESI†). Additionally, we obtained a certified efficiency of 19.50% from the Institute of Electrical Engineering, Chinese Academy of Sciences (Fig. S28 (ESI†); Report No. PWQC-WT-P24032522-2R). In addition, with incorporation of 3 wt% TA in the PM6 : L8-BO system, a stable PCE of 18.86%, along with a V_OC of 0.887 V, a J_SC of 27.15 mA cm⁻², and FF of 78.3%, were achieved (Fig. S29, ESI†). The J_SC value calculated from the external quantum efficiency (EQE) curve was consistent with the J_SC value obtained from the J–V curve (average deviation = <5%; Fig. 3B).
通过制造由玻璃/ITO/4PADCB/活性层/PNINN/银组成的刚性器件，对光伏性能进行了评估。† 电流密度-电压（J-V ）特性是在 AM 1.5G 模拟 1 太阳光照下的特性（Fig. 3A 和图 S25，ESI†），相关光伏参数汇总于表 1 和图 S3-S5（ESI†）。由于 4PADCB 具有出色的透射率和高功函数，因此使用 4PADCB 自组装单层取代了典型的 PEDOT:PSS (4083) 空穴传输层。基于 4PADCB 的 PM6 ：BTP-eC9 二元器件的 PCE 提高了 18.97%。最佳三元器件的 PCE 值（19.84%）、V_OC 0.863 V，短路电流密度（J_SC ）为 28.97 mA cm^-2 ，填充因子 (FF) 为 79.4%，是迄今为止报告的最高值。这些数值可归因于加入了 3 wt% TA 和 10 wt% D18-2F 作为客体受体。图 S26 和 S27（ESI†）显示了其他 TA 和 D18-2F 比率的器件参数，表 S4 和 S5（ESI†）汇总了相应的光伏参数。此外，我们还从中国科学院电工研究所获得了 19.50% 的认证效率（图 S28（ESI†）；报告编号：PWQC-WT-P24032522-2R）。 此外，在 PM6 ：此外，在 PM6 : L8-BO 体系中加入 3 wt% TA 后，PCE 稳定在 18.86%，V_OC 0.887 V，J_SC 为 27.15 mA cm^-2 ，FF 为 78.3%（图 S29，ESI†）。根据外部量子效率 (EQE) 曲线计算出的 J_SC 值与 J_SC 值与 J-V 曲线得出的值一致（平均偏差 = <5data-dl-uid="27">图 3B）。3B）。

A schematic of the prepared F-OSC is shown in Fig. 3G. The fabrication procedure is described in the ESI.† The J–V curve of this device is shown in Fig. 3H. An excellent PCE of 18.32%, a V_OC of 0.858 V, a J_SC of 27.76 mA cm⁻², and a FF of 76.9%, were achieved due to the presence of the 3 wt% TA-doped PM6 : D18-2F:BTP-eC9 blend as the active layer. This is consistent with the photovoltaic performances of devices comprising glass substrates. To the best of our knowledge, our flexible device is one of the highest-performing flexible devices reported to date (Fig. 3I).
图 3G 中显示了制备的 F-OSC 的示意图。† 该器件的 J-V 曲线如 图 3H 所示。出色的 PCE 为 18.32%，V_OC 为 0.858 V，J_SC 为 27.76 mA cm^-2 和 76.9% 的 FF，这是由于存在 3 wt% TA 掺杂的 PM6：D18-2F:BTP-eC9 混合物作为活性层。这与使用玻璃基底的设备的光伏性能相符。据我们所知，我们的柔性器件是迄今为止报告的性能最高的柔性器件之一（图 3I）。

The charge carrier and trap-assisted recombination of the devices were studied based on the dependence of the cell parameters (J_SC and V_OC) on the illumination intensity (P). The n values of thePM6 : BTP-eC9, 3 wt% TA-doped PM6 : BTP-eC9, and 3 wt% TA-doped PM6 : D18-2F : BTP-eC9 devices were 1.38, 1.22, and 1.20 kT q⁻¹, respectively (Fig. 3C). The fact that the n values are close to 1, indicates that bimolecular recombination barely occurred. This implies that the introduction of TA into the active layer improves its ability to suppress trap-assisted recombination, due to the better phase separation, resulting in a higher V_OC. The relationship between J_sc and P can be expressed as J_sc ∝ P^α, where α represents the degree of bimolecular recombination. The TA-doped PM6 : D18-2F : BTP-eC9-based device had an α closest to 1 (see Fig. 3D), indicating a slightly lower second-order recombination degree, and thus higher J_SC and V_OC values. The exciton dissociation (η_diss) and collection (η_coll) processes are critical to cell performance. The calculation method is described in the ESI.† The dependence of the photocurrent density (J_ph) on the effective voltage (V_eff) of the OSC was investigated (Fig. 3E). The calculated η_diss and η_coll values for PM6 : BTP-eC9 were 97.11 and 85.23%, for 3 wt% TA-doped PM6 : BTP-eC9 were 97.50 and 86.85%, and for 3 wt% TA-doped PM6 : D18-2F : BTP-eC9 were 97.95 and 91.68%, respectively. Among all the devices, the 3 wt% TA-doped PM6 : D18-2F : BTP-eC9 based device showed the highest η_coll, which may be ascribed to its nano-morphology and rational intermixed domain. Subsequently, the influence of TA on the charge transport properties of the OSC was analyzed through space-charge limited current (SCLC) measurements (described in the ESI†). The electron (μ_e) and hole (μ_h) mobilities of the TA-doped PM6 : D18-2F : BTP-eC9-based device were significantly improved (1.09 × 10⁻³ and 9.62 × 10⁻⁴ cm² V⁻¹ s⁻¹ respectively) compared to those of the PM6 : BTP-eC9-based device (5.97 × 10⁻⁴ and 4.35 × 10⁻⁴ cm² V⁻¹ s⁻¹ respectively) (Fig. 3F and Fig. S30, Table S6, ESI†), indicating more balanced hole and electron transport.
根据电池参数（J_SC 和 V_OC ）对照明强度（P ）的依赖关系，研究了器件的电荷载流子和陷阱辅助重组。PM6、BTP-eC9、3 w w 的 n 值：BTP-eC9、3 wt% TA 掺杂的 PM6 ：BTP-eC9、3 wt% TA 掺杂的 PM6：BTP-eC9 和 3 wt% TA 掺杂的 PM6：D18-2F：D18-2F ：BTP-eC9器件的q^-1分别为1.38、1.22和1.20 kT（图3C）。n值接近 1 的事实表明，双分子重组几乎没有发生。这意味着在有源层中引入 TA 后，由于相分离效果更好，抑制陷阱辅助重组的能力得到了提高，从而产生了更高的 V_OC 值。J_sc 和 P 之间的关系可表示为 J_sc ∝ P^α 、其中 α 表示双分子重组的程度。掺杂 TA 的 PM6 ：D18-2F ：基于 BTP-eC9 的器件的 α 最接近于 1（见 图 3D ），表明二阶重组程度略低，因此 J_SC 和 V_OC 值较高。激子解离（η_diss ）和收集（η_coll ）过程对细胞性能至关重要。 计算方法见 ESI。† 研究了 OSC 的光电流密度（J_ph ）与有效电压（V_eff ）的关系（Fig.3E）。计算得出的 PM6 的 η_diss 值和 PM6 的 η_coll 值分别为 97.9%和 97.9%：BTP-eC9分别为97.11%和85.23%，而掺杂3 wt% TA的PM6 : BTP-eC9分别为97.11%和85.23%：BTP-eC9分别为97.50%和86.85%，而掺杂3 wt% TA的PM6 ：D18-2F ：BTP-eC9分别为97.95%和91.68%。在所有器件中，掺杂 3 wt% TA 的 PM6 ：D18-2F ：η_coll ，这可能归因于其纳米形态和合理的混合域。随后，通过空间电荷限流 (SCLC) 测量分析了 TA 对 OSC 电荷传输特性的影响（详见 ESI† ）。电子（μ_e ）和空穴（μ_h ）的迁移率在掺杂 TA 的 PM6 ：D18-2F ：与基于 PM6 : D18-2F : BTP-eC9 的器件相比，基于 TA 掺杂的 PM6 : D18-2F : BTP-eC9 器件的迁移率显著提高（分别为 1.09 × 10^-3 和 9.62 × 10^-4 cm² V^-1 s^-1 ）：基于 BTP-eC9 的设备（5.97 × 10^-4 和 4.35 × 10^-4 cm² V^-1 s^-1 ）（Fig. S30，表 S6，ESI† ），表明空穴和电子传输更加平衡。

Blend morphology and exciton dynamics
混合形态和激子动力学

To further understand the underlying effects of using TA and D18-2F as guest acceptors on the charge transfer process and recombination behavior of the PM6 : BTP-eC9 system, femtosecond transient absorption spectroscopy measurements were performed. Fig. 4A–D and Fig. S32 (ESI†) show the 2D transient absorption spectra recorded at several time delays for the blend film, with an excitation wavelength of 400 nm for the donors to initiate electron transfer. The negative signals at ∼630 nm and ∼840 nm were attributed to the ground-state bleaching (GSB) of the donors and acceptors, respectively. The positive peak at ∼970 nm can be attributed to the local excited-state absorption (ESA) of the acceptor, which is consistent with the absorption of the neat acceptor films. At 400 nm excitation, the response of the 3 wt% TA-doped PM6 : BTP-eC9 and PM6 : D18-2F : BTP-eC9 systems at 630 nm is weaker than that of the binary system, which suggests enhanced charge transfer between the donor and acceptor. To further investigate the hole transfer dynamics, a pump light with a wavelength of 800 nm was employed (Fig. S33, ESI†). The appearance of donor GSB signals can intuitively reveal obvious hole transfer processes in the binary and ternary blend films. The decay kinetics of the GSB blend films probed at 633 nm (pump at 400 nm) were compared (Fig. S34, ESI†). The decay to the ground state of the 3 wt% TA-doped PM6 : D18-2F : BTP-eC9 ternary system is slower than that of the PM6 : BTP-eC9 binary host system, which indicates that the optimized morphology of the active layer has a lower trap state density and, consequently, a high FF value.
为了进一步了解使用 TA 和 D18-2F 作为客体受体对 PM6 : BTP-eC9 体系的电荷转移过程和重组行为的潜在影响，我们进行了飞秒瞬态吸收光谱测量。图 4A-D 和图 S32（ESI†）显示了混合薄膜在多个时间延迟下记录的二维瞬态吸收光谱，激发波长为 400 纳米，供体启动电子转移。在 ∼630 nm 和 ∼840 nm 处的负信号分别归因于供体和受体的基态漂白（GSB）。970 nm 处的正峰值可归因于受体的局部激发态吸收（ESA），这与纯受体薄膜的吸收一致。在 400 nm 激发下，掺杂 3 wt% TA 的 PM6 ：BTP-eC9 和 PM6 ：D18-2F ：BTP-eC9体系在630 nm波长处的响应弱于二元体系，这表明供体和受体之间的电荷转移增强了。为了进一步研究空穴传输动力学，使用了波长为 800 nm 的泵浦光（图 S33，ESI†）。供体 GSB 信号的出现可以直观地揭示二元和三元共混薄膜中明显的空穴传输过程。我们比较了在 633 纳米波长（泵浦波长为 400 纳米）下探测的 GSB 混合薄膜的衰变动力学（图 S34，ESI†）。掺杂 3 wt% TA 的 PM6 : D18-2F : BTP-eC9 三元体系衰减到基态的速度比 PM6 : BTP-eC9 二元宿主体系慢，这表明活性层的优化形态具有较低的陷阱态密度，因此 FF 值较高。

In addition, the quenching kinetics of the blend film with and without TA were probed by in situ photoluminescence (PL) measurements. The time-scale PL contour maps and the in situ PL spectra during the first 0.5 s of spin coating are shown in Fig. 4C and F. After the PL intensity reached its maximum, it began to decrease because of the gradual formation of a donor/acceptor mixed phase in the blended films, allowing the fluorophore and quencher to interact. Finally, the PL intensity is completely quenched after the completion of the donor/acceptor network formation. The 3 wt% TA-doped PM6 : BTP-eC9 blend film exhibited faster quenching (0.3 s) than the PM6 : BTP-eC9 binary blend film (0.4 s). This result may be attributed to the aggregation of the donor/acceptor network induced by the crosslinked TA in the film state. This suggests that our crosslinking strategy affects the crystalline arrangement and the formation of the nano-morphology of the active layer.
此外，还通过原位光致发光（PL）测量探究了有 TA 和无 TA 混合膜的淬火动力学。 图 4C 和 F 中显示了旋涂过程中最初 0.5 秒的时间尺度 PL 等值线图和 原位PL 光谱。PL 强度达到最大值后开始下降，这是因为在混合薄膜中逐渐形成了供体/受体混合相，使荧光团和淬灭剂能够相互作用。最后，在供体/受体网络形成完成后，PL 强度完全熄灭。掺杂 3 wt% TA 的 PM6 : BTP-eC9 共混薄膜的淬灭时间（0.3 秒）比 PM6 : BTP-eC9 二元共混薄膜的淬灭时间（0.4 秒）更快。这一结果可能是由于在薄膜状态下交联的 TA 诱导了供体/受体网络的聚集。这表明我们的交联策略影响了活性层的晶体排列和纳米形态的形成。

Cryogenic transmission electron microscopy (cryo-TEM) was used to observe the aggregation behavior and the dispersion structures of photovoltaic materials in liquid suspensions that are close to their native state.^52–54 The pre-aggregation state of the polymer typically controls the film morphology. Hence, after rapidly freezing the photovoltaic material precursor solutions, the pre-aggregation state dispersed in the solution was visualized and characterized by high-resolution (Fig. 5A and B and Fig. S35, ESI†). The concentrations of all frozen precursor solutions were 2 mg mL⁻¹. Fig. 5A shows the cryo-TEM images of the frozen PM6 (TA) chloroform solutions, in which the diffraction signals of parallel fringes were observed. This is consistent with an ideal interpenetrating network morphology in heterojunction blend films prepared from solution. The parallel fringes are more ordered in the bulk and more disordered at the edges (Fig. 5A). Moreover, densely distributed small parallel fringes were observed in the PM6 film; however, the sizes of the parallel fringes in the TA-doped films were larger than those of the PM6 film (Fig. 5B). The parallel fringes in the TEM images are marked with yellow lines in Fig. 5B. The cryo-TEM results indicate that TA plays an important role in the aggregation behavior of the solutions. Moreover, the different sizes and shapes of the aggregates in solution would affect the final film morphology of OSCs prepared from solution.
^52-54 低温透射电子显微镜（cryo-TEM）用于观察光伏材料在接近原生状态的液体悬浮液中的聚集行为和分散结构。因此，在快速冷冻光伏材料前驱体溶液后，分散在溶液中的预聚集状态通过高分辨率进行了可视化和表征（ 图 5A 和 B 和图 S35，ESI†）。所有冷冻前体溶液的浓度均为 2 毫克毫升^-1。图 5A 显示了冷冻的 PM6 (TA) 氯仿溶液的冷冻-TEM 图像，其中观察到平行条纹的衍射信号。这与溶液制备的异质结混合薄膜中理想的互穿网络形态一致。平行条纹在主体部分更有序，而在边缘部分更无序（图 5A）。此外，在 PM6 薄膜中也观察到了密集分布的小平行条纹；然而，掺杂 TA 的薄膜中平行条纹的尺寸比 PM6 薄膜中的要大（图 5B）。图 5B 中用黄线标出了 TEM 图像中的平行条纹。低温 TEM 结果表明，TA 在溶液的聚集行为中起着重要作用。此外，溶液中不同大小和形状的聚集体会影响由溶液制备的 OSC 的最终薄膜形态。

To gain further insight into the morphological evolution, GIWAXS measurements of the blended films were performed, and the crystallographic parameters of the films are summarized in Table S8 (ESI†). Fig. 5c shows the crystallinity and packing orientation of the blend films; all films possessed a face-on orientation, which facilitates charge transport in the OSCs. The CCLs in the OOP (010) direction of the TA-doped binary and ternary systems increased to 23.51 and 23.46 Å, respectively, from that of the binary system (20.94 Å), indicating more orderly molecular packing and a slight enhancement in crystallinity.
为了进一步了解形态演变，对混合薄膜进行了 GIWAXS 测量，表 S8（ESI†）汇总了薄膜的晶体学参数。图 5c 显示了混合薄膜的结晶度和堆积方向；所有薄膜都具有面朝上的方向，这有利于 OSC 中的电荷传输。掺杂 TA 的二元体系和三元体系在 OOP (010) 方向上的 CCL 分别从二元体系的 20.94 Å 增加到 23.51 Å 和 23.46 Å，表明分子堆积更有序，结晶度略有提高。

Mechanical properties of the blend film and thermal stability
混合薄膜的机械性能和热稳定性

A schematic of the intermolecular interactions in the PM6 : BTP-eC9, TA-doped PM6 : BTP-eC9, and TA-doped ternary blend films is presented in Fig. 6A, which illustrates the dissipation of tensile energy in the crosslinked network and the entanglement of the frozen morphology. The stretchability of blend films (Fig. 6B) is comparable to that of pristine donor films (Fig. 1h), with the 3 wt% TA-doped PM6 : D18-2F-based blend film obtaining the highest COS_FOW. All the characterization results are shown in Fig. 6C and Table S9 (ESI†). The COS_FOW of the 3 wt% TA-doped PM6 : D18-2F : BTP-eC9 film is 76.58% higher than that of the PM6 : BTP-eC9 binary film (3.63%). This suggests that a crosslinked network can effectively limit the formation and spread of cracks under extreme mechanical strains. In addition, high-molecular-weight D18-2F is more conducive to network entanglement, which enables the distribution of load across the length of the chains, thereby dissipating tensile energy.
图 6A 展示了 PM6 : BTP-eC9、掺杂 TA 的 PM6 : BTP-eC9 和掺杂 TA 的三元共混薄膜中的分子间相互作用示意图，说明了交联网络中拉伸能量的耗散和冻结形态的缠结。共混薄膜（图 6B）的拉伸性与原始供体薄膜（图 1h）相当，掺杂 3 wt% TA 的 PM6 ：基于 D18-2F 的混合薄膜获得了最高的 COS_FOW。所有表征结果见图 6C 和表 S9（ESI†）。掺杂 3 wt% TA 的 PM6 : D18-2F : BTP-eC9 薄膜的 COS_FOW 比 PM6 : BTP-eC9 二元薄膜的 COS_FOW 高 76.58%（3.63%）。这表明，在极端机械应变下，交联网络可有效限制裂纹的形成和扩展。此外，高分子量的 D18-2F 更有利于网络缠结，从而使负载分布在链的长度上，从而耗散拉伸能量。

In this study, for the first time in the literature, we used the efficiency deformation factor (EDF) to comprehensively evaluate the photovoltaic performance and mechanical robustness of active layer films. EDF is expressed as follows:
在本研究中，我们首次在文献中使用了效率变形因子（EDF）来综合评价活性层薄膜的光伏性能和机械稳健性。EDF 表示如下 EDF = PCE × COS_FOW where the PCE is obtained from the corresponding blend film-based flexible device and COS_FOW is obtained from the FOW method. The EDF of the PM6 : BTP-eC9 and 3 wt% TA-doped ternary blend films was 0.624 and 1.18%, respectively. The EDF of the optimal TA-doped ternary blend film was nearly two times that of the PM6 : BTP-eC9 binary blend film, which proves that in situ crosslinking can significantly improve the comprehensive performance of F-OSCs. Subsequently, to meet the requirements of wearable electronic devices, the mechanical robustness of F-OSCs against repetitive, harsh deformation was studied by monitoring the changes in the PCE of as a function of the number of bending cycles (r = 8 mm), and the results are shown in Fig. S36 (ESI†). After 1000 consecutive bending cycles, the PCEs of the TA-doped ternary F-OSCs remained at 98% of their initial values. Above 96% of the initial efficiency was retained even after 5000 bending cycles, demonstrating excellent mechanical flexibility.
其中，PCE 由相应的基于混合薄膜的柔性器件获得，COS_FOW 由 FOW 方法获得。PM6 ：BTP-eC9 和 3 wt% TA 掺杂三元共混薄膜的 EDF 分别为 0.624% 和 1.18%。最佳掺杂 TA 的三元共混薄膜的 EDF 几乎是 PM6 ：这证明原位交联能显著提高 F-OSC 的综合性能。随后，为了满足可穿戴电子设备的要求，我们通过监测 F-OSC 的 PCE 随弯曲循环次数（r = 8 mm）的变化，研究了 F-OSC 抵抗重复、恶劣变形的机械稳健性，结果如图 S36 所示（ESI†）。经过 1000 次连续弯曲循环后，掺杂 TA 的三元 F-OSC 的 PCE 保持在初始值的 98%。即使在经过 5000 次弯曲循环后，初始效率仍保持在 96% 以上，显示出出色的机械灵活性。

The storage lifetime of OSCs is another extremely important parameter. Therefore, inverted OSCs with glass/ITO/ZnO/active layer/MoO₃/Ag structures were fabricated to investigate their long-term and light stability. All tests were performed in a N₂-filled glove box without encapsulation. The normalized PCE, V_OC, and FF of the OSCs comprising different active layers as a function of time are shown in Fig. 6D and E. The degradation of the binary devices in the early stages is mainly caused by V_OC reduction, which is attributed to the formation of excessive phase domains under thermal stress. Subsequently, the V_OC and FF of the PM6 : BTP-eC9 device decreased sharply, resulting in a PCE of only 83.6% of the initial efficiency after 1512 h. This is attributed to the frozen nano-morphology of the active layer, which effectively dissipates large thermal stress and limits the diffusion and aggregation of NF-SMAs. However, the PCE of the optimized device was >93% of the initial efficiency even after 1500 h of thermal aging. Furthermore, almost no degradation was observed in the PCE of the TA-doped ternary device without encapsulation after storage in an N₂-filled glove box at room temperature for over 1848 h (Fig. S37, ESI†). As shown in Fig. S38 (ESI†), the photostability of the devices was further investigated under continuous exposure to 1 sun irradiation (100 mW cm⁻²). During the initial 24 hours, the device based on PM6 : BTP-eC9 with 3 wt% TA doping exhibited slightly better stability compared to the binary device. Subsequently, the rate of PCE decay of the devices slowed, with the 3 wt% TA doped PM6 : BTP-eC9-based device retaining 91% of its initial efficiency after 144 hours. A comparison of the mechanical and photovoltaic performances of the OSCs with PM6 : BTP-eC9 and TA-doped PM6 : BTP-eC9 as the active layer is shown in Fig. 6F.
OSC 的存储寿命是另一个极其重要的参数。因此，我们制作了具有玻璃/ITO/氧化锌/活性层/MoO₃/Ag 结构的倒置 OSC，以研究其长期稳定性和光稳定性。所有测试均在无封装的 N₂ 填充手套箱中进行。由不同活性层组成的 OSC 的归一化 PCE、V_OC 和 FF 随时间变化的情况如 图 6D 和 E 所示。二元器件在早期阶段的劣化主要是由 V_OC 降低引起的，这归因于在热应力作用下形成了过多的相域。随后，V_OC 和 PM6 ：这归因于活性层的冻结纳米形态，它有效地消散了大的热应力并限制了 NF-SMA 的扩散和聚集。不过，即使经过 1500 小时的热老化，优化器件的 PCE 仍大于初始效率的 93%。此外，没有封装的掺杂 TA 的三元器件在室温充满 N₂ 的手套箱中存储超过 1848 小时后，PCE 几乎没有下降（图 S37，ESI† ）。如图 S38 所示（ESI†），在连续暴露于 1 个太阳光照射（100 mW cm^-2）下，进一步研究了器件的光稳定性。 在最初的 24 小时内，基于 PM6 ：与二元器件相比，掺杂了 3 wt% TA 的 PM6 : BTP-eC9 器件的稳定性稍好。随后，器件的 PCE 衰减速度减慢，掺杂 3 wt% TA 的 PM6 ：基于 BTP-eC9 的器件在 144 小时后保持了 91% 的初始效率。对含有 PM6 ：BTP-eC9 和掺杂 TA 的 PM6 ：图 6F 中显示了以 PM6 : BTP-eC9 和 TA 掺杂 PM6 : BTP-eC9 作为活性层的 OSC 的机械和光电性能比较。

Conclusion  结论

In this study, a crosslinking monomer, thioctic acid (TA), with dynamic covalent disulfide and H-bonds, was doped into the active layer and carefully developed in photovoltaic blend films. The thermal annealing process that occurs during the preparation of the blend film induces the in situ formation of crosslinked networks, which fine-tune the molecular crystallinity and stacking while achieving a frozen nano-morphology with excellent deformability. The crack-onset strains (COS_FOW) of the optimized donor- and blend-based films determined by the film-on-water (FOW) tensile test were 14.25% and 6.44%, respectively. These values were attributed to the crosslinked network, which dissipates the mechanical stress induced by the tensile test. The stabilized power conversion efficiencies (PCE) of the rigid and flexible devices were 19.84% and 18.32%, respectively. This is the highest reported PCE for an F-OSC thus far. Furthermore, the optimal flexible organic solar cells (F-OSCs), i.e., TA-doped PM6 : D18-2F : BTP-eC9 photovoltaic blend film, exhibited excellent mechanical tolerance and a PCE retention of >96% even after 5000 bending cycles. In addition, the device showed thermal stress tolerance and maintained 93% of its initial PCE even after 1500 h of storage in an N₂-filled glove box at 85 °C. Our strategy of inducing the formation of an in situ crosslinked matrix in a donor/acceptor blend could promote the development of high-performance F-OSCs.
本研究在活性层中掺入了具有动态共价二硫键和氢键的交联单体硫辛酸 (TA)，并在光伏共混薄膜中进行了细致的开发。混合薄膜制备过程中的热退火过程诱导了交联网络的原位形成，从而对分子结晶度和堆积进行了微调，同时获得了具有优异变形能力的冻结纳米形态。通过水上薄膜（FOW）拉伸试验测定的优化供体薄膜和混合薄膜的开裂应变（COS_FOW ）分别为 14.25% 和 6.44%。这些数值归功于交联网络，它可以消散拉伸试验引起的机械应力。刚性和柔性器件的稳定功率转换效率（PCE）分别为 19.84% 和 18.32%。这是迄今为止报告的最高 F-OSC 功率转换效率。此外，最佳柔性有机太阳能电池（F-OSCs），即，掺杂 TA 的 PM6 ：D18-2F ：BTP-eC9 光伏混合薄膜表现出卓越的机械耐受性，即使在 5000 次弯曲循环后，其 PCE 保持率仍大于 96%。此外，该器件还具有热应力耐受性，在 85 °C、充满 N₂ 的手套箱中存放 1500 小时后，仍能保持 93% 的初始 PCE。我们在供体/受体混合物中诱导形成原位交联基质的策略可促进高性能 F-OSC 的开发。

Author contributions  作者供稿

W. S. conceived the idea, and performed the fabrication and characterization of devices. C. L. and R. P. synthesized the target material D18-2F. P. Z. and Y. X. performed the TEM measurement and analyzed the results. Z. C., D. S., W. Z. and J. G. provided feedback regarding overall data analysis. The project was supervised and directed by Z. G. W. S. wrote the manuscript with large contributions from L. X., D. Y. Q. L. and Z. G. All authors commented on the manuscript for improvements.
W.S. 构想了这一想法，并完成了设备的制造和表征。C. L. 和 R. P. 合成了目标材料 D18-2F。P. Z. 和 Y. X. 进行了 TEM 测量并分析了结果。Z. C.、D. S.、W. Z.和 J. G.对整体数据分析提供了反馈意见。该项目由 Z. G. 和 W. S. 负责监督和指导，L. X. 、D. Y. Q. L. 和 Z. G. 参与了手稿的撰写，所有作者都对手稿提出了改进意见。

Data availability  数据可用性

The data supporting this article have been included as part of the ESI.†
支持本文的数据已作为 ESI.† 的一部分收录。

Conflicts of interest  利益冲突

The authors declare no conflict of interest.
作者声明没有利益冲突。

Acknowledgements 致谢

This work was financially supported by the National Science Fund for Distinguished Young Scholars (21925506), the National Natural Science Foundation of China (22309196 and 22279152), the China Postdoctoral Science Foundation (2023M743625), the Zhejiang Provincial Natural Science Foundation of China (LQ24F050008), the Ningbo Natural Science Foundation (2023S126), the Ningbo key scientific and technological project (2022Z117), and the China National Postdoctoral Program for Innovative Talents (BX20230386).
这项工作得到了国家杰出青年科学基金（21925506）、国家自然科学基金（22309196和22279152）、中国博士后科学基金（2023M743625）、浙江省自然科学基金（LQ24F050008）、宁波市自然科学基金（2023S126）、宁波市重点科技项目（2022Z117）和国家博士后创新人才计划（BX20230386）的资助。

References 参考资料

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