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

Abstract

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, were 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 was elucidated.

Heterogeneity at multiple length scales in halide perovskite semiconductors

“…It may even be possible to efficiently transport charges over these super-grain entities, which opens up the possibility for efficient lateral or rear-contact solar cell devices 195,196 .…”

Curing perovskites—a way towards control of crystallinity and improved stability

“…For the common planar type architecture, where a perovskite layer of a few hundred nm thickness is sandwiched between charge selective layers, grain sizes on that same length scale are usually sufficient to span both electrodes to ensure unhindered charge transport. When, however, the hunt for record efficiencies moves perovskite research towards back-contacted architectures as it has for conventional photovoltaics, the superior lateral conductivity of grains bridging many micrometers between electrodes may become essential for efficient charge extraction [15,41,42].…”

Simple, Robust, and Going More Efficient: Recent Advance on Electron Transport Layer‐Free Perovskite Solar Cells

“…[127] Such a nonsymmetric backcontacted device platform is also helpful for understanding the effect of film morphology on the optoelectrical property and the final device performance. However, the small charge-carrier diffusion length within the polycrystalline perovskite film relative to the grating electrode spacing can limit the device performance.…”

“…However, the small charge‐carrier diffusion length within the polycrystalline perovskite film relative to the grating electrode spacing can limit the device performance. By changing the perovskite films grain sizes in the bc‐PSC, Bach and co‐workers further found that the charge‐carrier diffusion length is crystal‐size dependent and the device performance correlates positively with the perovskite grain size . Such a nonsymmetric back‐contacted device platform is also helpful for understanding the effect of film morphology on the optoelectrical property and the final device performance.…”