Interfacial modification by 2-fluoroisonicotinic acid enabling high-efficiency and stable n-i-p perovskite solar cells

The power conversion efficiency (PCE) of organic-inorganic halide perovskite solar cells (PSCs) developed rapidly in recent years. However, the defects at the bulk grain boundaries and heterojunction interfaces acting as non-radiative recombination centres and the ion-migration channels severely hinder the charge transport and stability of the PVKs, resulting in low PCE and poor stability. One of the principal impediments to the commercialization of PSCs resides in the challenge posed by this particular aspect. In this work, we employed 2-fluoroisonicotinic acid (2-FINA) as a passivation agent to improve the PCE and stability of n-i-p PSCs by interfacial modification strategy. Owing to the presence of carboxyl (COOH) functional groups and pyridine groups, 2-FINA can strongly interact with uncoordinated Pb 2+ and regulate the growth of perovskite crystals, which in turn reduces ion migration and suppress non-radiative recombination along with improves optical properties. Thanks to these improvements, the champion n-i-p PSC solar cell, treated with 2-FINA, showed a PCE of 20.92 %, whereas the untreated one in the same batch exhibited a PCE of 17.13 %. In long-term stability tests, we demonstrated that 2-FINA treatment significantly increases the moisture resistance of non-encapsulated devices.