Monolithic Perovskite Solar Capacitor Enabled by Double-Sided TiO₂ Nanotube Arrays

An integrated power pack that renders simultaneous solar energy harvesting and storage represents a particularly promising energy source toward future applications. Herein, we report a high-performance hybrid power pack of perovskite solar cell (PSC) and supercapacitor via capitalizing on double-sided TiO2 nanotube arrays that have a dual-function as electron transport layer (ETL) for PSC and cathode for supercapacitor, respectively (i.e., a monolithic perovskite solar capacitor). Specifically, a simple yet robust acid-treatment strategy followed by selective oxygen plasma exposure on only the PSC side is employed to concurrently increase the performance of double-sided TiO2 nanotube electrodes in both the PSC and supercapacitor units. Intriguingly, the integrated power pack delivers fast response under photocharging because of efficient charge transfer across the two sides of the TiO2 nanotube array electrode, attaining a high overall optoelectrical energy conversion and storage efficiency of 9.18%. This work demonstrates a viable route to engineering intimately linked energy conversion–storage systems of interest.