Impact of Additive-Induced Electric Polarization on Solar Cell Performance: CsPbI₃ as a Case Study

Additives are known to improve the performance of electronic devices, including perovskite solar cells, by forming homogeneous films and providing a smooth surface, which in turn creates a better interface with the charge transport layer. Furthermore, they often offer a suitable route to passivate defects in the perovskites. Interestingly, most of the additives being used in perovskite solar cells contain an electric dipole moment. We have thereby probed the electric polarization of additive-incorporated thin-films and, as a case study, considered CsPbI₃ films with a range of additives. In additive-incorporated perovskite thin-films, the piezoresponse force microscopy (PFM) studies derived the effective piezoelectric coefficient (d₃₃) and Kelvin probe force microscopy (KPFM) could probe a change in the surface potential upon a reversal of the poling direction; both the measurements have evidenced and quantified the electric polarization in the films. Upon fabricating p-i-n heterojunctions based on the additive-incorporated films and characterizing them, we observed that the solar cell parameters were well-correlated to the electric polarization of the active layer. We thereby have inferred that the additives provide a synergistic effect of improving film morphology and, more importantly, inducing electric polarization to better the solar cell parameters through an augmented charge separation and transport processes.