Grain boundary defect passivation and iodine migration inhibition for efficient and stable perovskite solar cells

Abstract

To inhibit the I⁻migration and passivate the uncoordinated Pb²⁺ on perovskite grain boundary (GB), 3-methyl-(1,1′-biphenyl)-4,4′-diformaldehyde (BPDA-Me) and 3-chlorine-(1,1′-biphenyl)-4,4′-diformaldehyde (BPDA-Cl) were synthesized and incorporated into perovskite films, respectively. The C = O groups in both additives can strongly interact with the uncoordinated Pb²⁺, allowing them to be anchored in perovskite GB. At the same time, the benzene ring skeleton in these two molecular structures can interact with the migrating I⁻ in GB. The Cl atom in the BPDA-Cl molecule delocalize electrons into the C = O group due to the conjugation effect of the benzene ring, so that the C = O group can provide stronger electronegativity, thus enhancing the interaction with the uncoordinated Pb²⁺. Meanwhile, Cl atom can coordinate with Pb²⁺ to synergically passivate the I vacancy defect on GB and enhance the lattice strength of PbI₆. This cooperative passivation further effectively inhibited the I⁻migration occurring at the perovskite GB. The functional group electron density regulation and cooperative passivation of Cl and C = O in BPDA-Cl make the passivation effect better than BPDA-Me. Consequently, the BPDA-Cl based perovskite solar cell achieved the highest power conversion efficiency of 24.96 % and stability with 92.1 % of the initial performance retained after 500 h of operation under continuous lighting and maximum power point tracking conditions.