Effect of Grain Cluster Size on Back-Contact Perovskite Solar Cells

Incorporating interdigitated back-contact electrodes into organic–inorganic halide perovskite solar cells overcomes the optical losses and low architectural defect tolerance present in conventional “sandwich” cell configurations. However, other factors limit device performance in back-contact architectures, such as the short charge-carrier diffusion length within the perovskite film relative to the electrode spacing. As charge-carrier diffusion length is crystal-size related, in order to understand the effect of perovskite morphology on the performance of back-contact perovskite solar cells (bc-PSCs), perovskite films with four different grain cluster sizes, i.e., large, medium, small, and extra small, are fabricated via a solvent annealing approach. Crystallization of the perovskite is found to be closely related to the surface chemistry and topography of the substrate. The bc-PSC photovoltaic performance correlates positively with the perovskite grain cluster size. Through a detailed analysis of transient photovoltage decay measurements, time-resolved photoluminescence, and space charge-limited current measurements, the effect of defect densities associated with grain cluster boundaries is elucidated.