Polymer molecule as nucleating agent to modulate crystallization kinetics for efficient and stable organic solar cells

The crystallization and aggregation characteristics of the active layer components in organic solar cells (OSCs) are one of the core factors determining photovoltaic performance, influencing the entire process from light absorption to charge separation, transport, and ultimately charge collection. Dynamic changes in crystallization and aggregation states can also disrupt the microstructure of the active layer, thus shortening the lifetime of the cell. In this study, a morphology modulation strategy is proposed to regulate the crystallization kinetics of non-fullerene acceptors by employing the polymer molecule PYIT as a nucleating agent. An appropriate amount of PYIT was first completely dissolved with the non-fullerene acceptor Y6 and left to stand for 24 h, followed by the fabrication of layer-by-layer processed OSCs. Experiments demonstrated that high crystallinity of PYIT allows it to act as a crystallization nucleus, promoting the crystallization, orientation consistency, and ordered stacking of the acceptor. These nanoscale structural optimizations facilitate efficient charge transport, enhance exciton dissociation efficiency, and suppress unfavorable energetic disorder. Consequently, not only was the power conversion efficiency (PCE) of D18-Cl/Y6-based layer-by-layer processed OSC increased from 18.08 % to 19.13 %, but the atmospheric stability and long-term lifetime of the OSCs were also significantly improved. Notably, this strategy is also applicable to indoor OSCs, and the PYIT-optimized device can achieve a PCE of 27.0 % under 1000 lux light-emitting diode (LED, 3200K) irradiation, which is superior to that of the control device (24.2 %). This work develops a crystal engineering strategy that is able to simultaneously optimize the microscopic morphology and charge dynamics properties in OSCs, thereby achieving simultaneous improvement in efficiency and stability.