Bilayer layer-by-layer structures for enhanced efficiency and stability of organic photovoltaics beyond bulk heterojunctions

Tuning bulk heterojunctions is an important step for improving organic photovoltaic device performance; however, challenges remain in obtaining sufficient device lifetimes using this concept. In this work, we report on high-performance PM6/Y7 layer-by-layer organic photovoltaic devices by carefully tuning the layer-by-layer structure and studying the effects on device performance. We demonstrate that an optimized layer-by-layer organic photovoltaic can effectively improve the photophysical properties of the device, resulting in a conversion efficiency of 16.21%, surpassing the bulk heterojunction counterpart. Notably, the developed layer-by-layer device also outperforms the traditional bulk heterojunction in terms of long-term photostability and thermal stability under continuous illumination and temperature stress (85°C) for approximately 1,000 h, with similar results obtained for eight other non-fullerene acceptor systems. The improved long-term photostability and thermal stability in these layer-by-layer systems is ascribed to a mitigation of the strong phase aggregation seen in the bulk heterojunction films.