Steric effect of amino-acids as additives for perovskite solar cells

• Proline is added in PSCs, exhibiting PCE=19.6%. • Orientational crystallization was realized by steric hindrance effect. In perovskite solar cells, the molecule configuration of Lewis adducts closely related with its coordination ability, which needs careful design. In this work, two amino acids, circular proline and linear glycine are applied to reveal the steric effect of the Lewis-acid base additives. The proline with configuration and analogous size with Pb-Pb distance in perovskite crystals realizes better coordination effect, greatly promotes the perovskite crystal growth and trap states passivation. The PSCs with proline as additives in perovskite (PVK) exhibit the highest efficiency of 19.6% under 1 sun AM1.5, compared with 18.5% of PSC with glycine additive and 17.8% of the pristine PSCs. This work highlights steric effect should be considered when choosing and designing the Lewis adducts.