Inverted organic solar cells with an in situ-derived SiOxNy passivation layer and power conversion efficiency exceeding 18%

Abstract

Inverted organic solar cells are attractive for commercialization. However, their power conversion efficiency (PCE) still lags their conventional architecture counterpart. Here we propose a new approach to enhance the performance and stability of structure-inverted non-fullerene organic solar cells. We use an in situ-derived inorganic SiO_xN_y passivation layer, formed by curing a solution-deposited perhydropolysilazane thin film in ambient atmosphere on top of the commonly used ZnO transport layer. Oxygen vacancies and dangling bonds of ZnO create a doped region in the photoactive layer, leading to losses in photocurrent due to enhanced recombination of photogenerated holes within this region. The optimized SiO_xN_y interlayer effectively passivates the ZnO surface defects by forming Zn–O–Si bonds, leading to a vanishing doped region. At the same time, SiO_xN_y induces a preferential accumulation of the non-fullerene acceptor near the electron contact, which also favours charge extraction. The combination of both effects leads to increased photocurrent density and PCE, with certified PCE values of 18.49% and 18.06% for cells with active areas of 5.77 mm² and 100.17 mm², respectively, using PM6:L8-BO as the photoactive layer. Importantly, cells containing inorganic SiO_xN_y exhibit an estimated T₈₀ lifetime of 24,700 h (where T₈₀ is the time it takes for the PCE to drop to 80% of its initial value) under white light illumination, corresponding to an operational lifespan exceeding 16 years. The results underscore the potential of our approach for practical applications of highly efficient and stable inverted organic solar cells.