Additive Engineering in Perovskite Solar Cells: Effect of Basicity of Benzoquinone Additives Controlled by Substituent

We report here the effect of the basicity of the passivation material on the photovoltaic parameters of perovskite solar cells (PSCs). Benzoquinone (BQ) derivatives were used as additives in the perovskite precursor solution to passivate grain-boundary defects on the perovskite film, where the basicity of the BQ was controlled by substituents using electron-donating methyl (tetramethyl-1,4-benzoquinone (4Me-BQ)) and electron-withdrawing chlorine groups (tetrachloro-1,4-benzoquinone (4Cl-BQ)). The control device without additive showed a power conversion efficiency (PCE) of 21.39% at the reverse scan that was improved to 23.05% by addition of 4Me-BQ, while the PCE was decreased to 18.21% by addition of 4Cl-BQ. A marginal change in PCE was observed for BQ (20.36%). The change in the Lewis basicity of the BQ by the substituent had an influence on the trap density and thereby the carrier lifetime of the perovskite films. Moreover, 4Me-BQ-treated PSCs demonstrated better stability than the control devices. This work provides important insight into the correlation of defect passivation with the degree of basicity of the passivation materials.