Effect of Hole Transport Layer on Energy Loss of Pervskite Solar Cell

The performance of perovskite solar cells (PVSCs) is most affected by the crystallinity of perovskite. Among several conditions, the interfacial properties between the charge transfer layer and the perovskite active layer, where the perovskite crystalline structure begins, are also one of the factors that have a great influence. Thus, various studies have been performed the ways to modify HTL to improve the device performance in the p-i-n structure. As the crystallinity including grain size of perovskite layers is influenced by the HTLs, the various charge dynamics will be also changed. Until now, however, there is little research related to energy loss analysis about the perovskite layer depending on HTLs. In this study, the difference in <i>V_oc</i> between PEDOT:PSS and NiO_x was explained through energy loss analysis. Despite the energy levels of PEDOT:PSS and NiO_x are similar to -5.0 eV and -5.1 eV, respectively, significant <i>V_oc</i> difference is observed between PEDOT:PSS based PVSCs (0.933 V) and NiO_x based PVSCs (1.088 V). Our energy loss analysis clearly indicated that this <i>V_oc</i> difference originated by non-radiative recombination. It is known that the non-radiative recombination in PVSCs is generally occurred by traps in the perovskite film, which is generated by grain boundary and defects of perovskite film. The perovskite film on NiO_x showed a larger grain size and improved crystallinity compared to the perovskite film on PEDOT:PSS. Therefore, we concluded that the increased<i> V_oc</i> in PVSCs using NiO_x HTL was due to the decrease in non-radiative recombination induced by the improved morphology.