Improvement of Open-Circuit Voltage Deficit via Pre-Treated NH4+ Ion Modification of Interface between SnO2 and Perovskite Solar Cells

Abstract

Passivation is a popular method to increase power conversion efficiency (PCE), reduce hysteresis related to surface traps and defects, and adjust mismatched energy levels. In this paper, an approach is reported using ammonium chloride (AC) to enhance passivation effects by controlling chlorine (Cl) and ammonium ions (NH4+) on the front and back side of tin oxides (SnO2). AC pre-treatment is applied to indium tin-oxide (ITO) prior to SnO2 deposition to advance the passivation approaches and compare the completely separated NH4+ and Cl passivation effects, and sole NH4+ is successfully isolated on the SnO2 surface, the counterpart of AC-post-treatment, generating ammonia (NH3) and Cl. It is demonstrated that multifunctional healing effects of NH4+ are ascribed from AC-pre-treatment being the basis of SnO2 crystallization and adjusting bifacial interface energy levels at ITO/SnO2 and SnO2/perovskite to enhance photo-carrier transport. As calculated by density functional theory, how the change of the passivation agent from Cl to NH4+ more effectively suppresses non-radiative recombination ascribed to hydrated SnO2 surface defects is explained. Consequently, enhancement of photo-carrier transport significantly improves a superior open-circuit voltage of 1.180 V and suppresses the hysteresis, which leads to the PCE of 22.25% in an AC-pre-treated device 3.000% higher than AC-post-treated devices.