Suppressing Non-Radiative Energy Loss in Organic Solar Cells: Molecular Design and Device Engineering

High Resolution Image Download MS PowerPoint Slide Conspectus Organic solar cells (OSCs), as one of the promising photovoltaic technologies, have garnered extensive attention. Thanks to the advancement in novel material development and the optimization of device engineering techniques, the power conversion efficiency (PCE) of OSCs has exceeded 20%, fully showcasing their immense potential for commercialization. Nevertheless, OSCs experience relatively substantial energy losses (0.5–0.6 eV) when compared to the high-performance inorganic solar cells, which consequently results in lower open-circuit voltages ( V oc ). Specially, the energy loss associated with the non-radiative recombination of charge carriers stands as the dominant energy-loss mechanism, severely hampering further improvement in photovoltaic performance. Inspired by the recent progress, we conduct a systematic investigation into non-radiative energy loss (Δ E nr ) in OSCs and summarize the strategies we adopted to suppress such losses. These efforts have played a significant role in propelling the efficiency of OSCs beyond the critical threshold of 20%, marking a momentous milestone in the field. In this Account, we first discuss the mechanism of non-radiative recombination and point out the dynamic and optoelectronic properties of the singlet excited (S 1 ) and charge-transfer (CT) states formed at the donor–acceptor interface has a great influence on the Δ E nr . Furthermore, the design rules of mitigating Δ E nr are summarized as follows: (1) Utilization of solid additives and ternary blend strategy–this can precisely control the molecular packing characteristics and optimize the morphological structure of the active layer. After these adjustments, the properties of the CT state are substantially improved, resulting in an effective reduction in Δ E nr . (2) Improvement of molecular planarity–this helps suppress molecular vibrations, reduce the reorganization energy, and simultaneously increase the photoluminescence quantum yield (PLQY) of the material. The synergistic action of these factors leads to a decrease in Δ E nr, thereby significantly enhancing the photovoltaic performance of the corresponding devices. (3) Incorporation of three-dimensional (3D) units into the acceptor–it can allow for effective regulation of its aggregation behavior and molecular packing. This, in consequence, suppresses the aggregation-caused quenching (ACQ) effect and thus raises the PLQY of the acceptor. (4) Halogenation treatment and side-chain engineering of polymer donors–these are effective methods to tune energy levels, reduce charge-transfer driving force at the donor–acceptor interface, and optimize dynamic properties of the S 1 and CT states, which can efficiently reduce the Δ E nr . At the end of this Account, we provide the possible strategies from the perspective of molecular design and device engineering to suppress the Δ E nr and take the photovoltaic performance of OSCs to the next level.