Unraveling the role of active hydrogen caused by carbonyl groups in surface-defect passivation of perovskite photovoltaics

The molecules with carbonyl group are regarded as ideal candidates to passivate surface-defects on metal halide perovskites. However, as an electron-withdrawing group, the CO groups are the ones that make hydrogen active on their adjacent atoms. Therefore, carbonyl compounds tend to produce keto-enol tautomerism and dissociation of hydrogen, which would affect their passivation effect. Herein, we chose three carbonyl-based molecules, morpholine, 3-morpholone and 3,5-morpholone with different amounts of carbonyl groups, to systematically investigate the effect of active hydrogen on their defect-passivation effect. The passivation effect of multifunctional molecule would be maximized when the molecule was in an optimal configuration with negligible active hydrogen. Consequently, a champion power conversion efficiency of 23.05% was approached with 3-morpholone surface treatment. The finding in this work reveals the importance of carbonyl distribution in molecular configuration when designing multifunctional passivation molecules in perovskite photovoltaics.