N-type small molecule electrolyte cathode interface layer with thickness insensitivity for organic solar cells

Interface engineering has a critical impact on the performances of organic solar cells (OSCs). And cathode interface layer (CIL) with thickness insensitivity is urgently pursued to improve the possibility of industrialization of OSCs. N-type self-doping has been proven effective in increasing electron mobility. Here, four novel n-type small molecule electrolytes (SMEs) with diverse counter anions (CAs), PDIN-BF4, PDIN-BPh4, PDIN-BPhF4, and PDIN-BIm4 were synthesized and employed as cathode interface layers (CILs). Among them, PDIN-BIm4-based OSCs with PM6:Y6 active layer achieved the most glorious electron mobility and thickness insensitivity with a power conversion efficiency (PCE) of 16.98 % due to outstanding self-doping effect and interfacial regulation ability. However, the multi-F atoms on PDIN-BPhF4 may prevent self-doping progress and impede electron transport, thus leading to a low PCE of 11.53 %. Meanwhile, the PDIN-BIm4-based device can maintain over 80 % of the optimal PCE with a thickness of 43 nm or storing in a glove box for 600 h. In addition, PM6: BTP-eC9-based device with PDIN-BIm4 CIL acquired a PCE of 17.82 %, highlighting the broad applicability of PDIN-BIm4. Our work demonstrates that the introduction of CAs into n-type organic materials helps promote the progress of efficient and stable OSCs.