A donor: hole-transport layer alloy for high-efficiency and stable binary organic solar cells with promoted hole collection and suppressed recombination

Charge collection efficiency is primarily dependent on the interface layer in organic solar cells (OSCs), minimizing the recombination at interface can effectively suppress energy losses. A persistent challenge remains in the development of hole-transport materials that can establish intimate contact with organic photoactive materials, primarily due to their hydrophilic nature. Here, we incorporated water-based nanoparticles (NPs) containing donor material into the conventional PEDOT:PSS to fabricate the hole-transport layer (HTL) in OSC devices. This strategy creates an extensively intermixed donor:PEDOT:PSS alloy, which optimizes the work function, reduces energy loss, and significantly increases the interface area between the HTL and the photoactive layer. The alloy formation promotes high crystallinity in the active layer, facilitating charge collection and suppressing non-radiative recombination. OSCs based on this approach, particularly those using PM6:L8-BO, achieved an efficiency of 19.9 % (19.3 % certified). Inverted device retained 95 % of its initial efficiency after 1600 hours of continuous illumination, marking one of the best stability records for PM6:L8-BO-based OSCs. This novel approach addresses the incompatibility issues between solution-processed HTLs and active layers in OSCs, offering significant promise for future advancements in organic solar cell research about interface engineering.