Improvement of Open-Circuit Voltage Deficit via Pre-Treated NH 4 + Ion Modification of Interface between SnO 2 and Perovskite Solar Cells.

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 (NH 4 + ) on the front and back side of tin oxides (SnO 2 ). AC pre-treatment is applied to indium tin-oxide (ITO) prior to SnO 2 deposition to advance the passivation approaches and compare the completely separated NH 4 + and Cl passivation effects, and sole NH 4 + is successfully isolated on the SnO 2 surface, the counterpart of AC-post-treatment, generating ammonia (NH 3 ) and Cl. It is demonstrated that multifunctional healing effects of NH 4 + are ascribed from AC-pre-treatment being the basis of SnO 2 crystallization and adjusting bifacial interface energy levels at ITO/SnO 2 and SnO 2 /perovskite to enhance photo-carrier transport. As calculated by density functional theory, how the change of the passivation agent from Cl to NH 4 + more effectively suppresses non-radiative recombination ascribed to hydrated SnO 2 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.