Efficient, Thermally Stable, and Mechanically Robust All‐Polymer Solar Cells Consisting of the Same Benzodithiophene Unit‐Based Polymer Acceptor and Donor with High Molecular Compatibility

Abstract

All‐polymer solar cells (all‐PSCs) are a highly attractive class of photovoltaics for wearable and portable electronics due to their excellent morphological and mechanical stabilities. Recently, new types of polymer acceptors (PAs) consisting of non‐fullerene small molecule acceptors (NFSMAs) with strong light absorption have been proposed to enhance the power conversion efficiency (PCE) of all‐PSCs. However, polymerization of NFSMAs often reduces entropy of mixing in PSC blends and prevents the formation of intermixed blend domains required for efficient charge generation and morphological stability. One approach to increase compatibility in these systems is to design PAs that contain the same building blocks as their polymer donor (PD) counterparts. Here, a series of NFSMA‐based PAs [P(BDT2BOY5‐X), (X = H, F, Cl)] are reported, by copolymerizing NFSMA (Y5‐2BO) with benzodithiophene (BDT), a common donating unit in high‐performance PDs such as PBDB‐T. All‐PSC blends composed of PBDB‐T PD and P(BDT2BOY5‐X) PA show enhanced molecular compatibility, resulting in excellent morphological and electronic properties. Specifically, PBDB‐T:P(BDT2BOY5‐Cl) all‐PSC has a PCE of 11.12%, which is significantly higher than previous PBDB‐T:Y5‐2BO (7.02%) and PBDB‐T:P(NDI2OD‐T2) (6.00%) PSCs. Additionally, the increased compatibility of these all‐PSCs greatly improves their thermal stability and mechanical robustness. For example, the crack onset strain (COS) and toughness of the PBDB‐T:P(BDT2BOY5‐Cl) blend are 15.9% and 3.24 MJ m–3, respectively, in comparison to the PBDB‐T:Y5‐2BO blends at 2.21% and 0.32 MJ m–3.

High-Molecular-Weight Electroactive Polymer Additives for Simultaneous Enhancement of Photovoltaic Efficiency and Mechanical Robustness in High-Performance Polymer Solar Cells

“…This notable enhancement in the mechanical ductility of the blends was attributed to tie molecules and chain entanglements formulated by the long chains of high-MW P A , dramatically improving the dissipation of external stress. 10 , 68 Based on the aforementioned results and the photovoltaic parameters presented in Figure 2 and Table 2 , the PSC incorporating 20 wt % of the P A demonstrates optimal photovoltaic performance (PCE exceeding 15%) and mechanical robustness (COS exceeding 10%). The PCEs and COS values (obtained by the pseudo-free-standing tensile test) of the PSCs developed in this study were compared with those of previously reported PSCs ( Figure 4 d and Table S6 ).…”

“…This brittleness of the Y7 thin film was attributed to its highly rigid ladder-type backbone structure, which is consistent with the reported characteristic brittleness of SMA materials. 10 , 12 In stark contrast, the P(NDI2OD-T2) P A had high ductility with a COS and toughness of 39.20% and 12.0 MJ m –3 , respectively. The superior ductility of P(NDI2OD-T2) was attributed to its high MW ( M w = 267 kg mol –1 ) exceeding its critical MW, which affords the formation of tie molecules and entangled chains in the thin film.…”

“… 9 More recently, we designed new polymerized SMAs which share the same building units with the polymer donors for better molecular compatibility, leading to both efficient (PCE ≈ 11%) and mechanically robust (COS ≈ 15%) PSCs. 10 However, although the mechanical properties of PSCs strongly rely on the molecular weights (MWs) of the consisting polymers, 12 , 21 − 24 polymerized SMAs having high MWs (above the critical MW) have not been achieved thus far. Moreover, the PSCs with polymerized SMAs still show a lower PCE than that of the state-of-the art SMA-based PSCs.…”

“…Moreover, the PSCs with polymerized SMAs still show a lower PCE than that of the state-of-the art SMA-based PSCs. 5 , 9 , 10 , 19 …”

Revealing the microstructure-related light-induced degradation for all-polymer solar cells based on regioisomerized end-capping group acceptors

“…16,18,19 Additionally, due to interchain entanglement between the polymer donor ( P D ) and the polymer acceptor ( P A ), the P A s are normally perceived to possess some unique stability properties like superior resilience against thermal and mechanical stress, as compared to the relevant fullerene and NFA materials. 10,20,21 Despite this, performance attenuation and morphological evolution in the relevant all-PSCs are still observed under increased thermal heating or even exposure to the ambient conditions. 22,23 In particular, appropriate investigations have initially shown that the material structure-determined stability was also present in the all-polymer systems.…”