Efficient planar perovskite solar cells prepared via a low-pressure vapor-assisted solution process with fullerene/TiO2 as an electron collection bilayer

Abstract

In perovskite solar cells (PSC), electron collection layers play a critical role in blocking holes and transporting electrons for high performances. In this study, a fullerene layer was introduced by a solution-process method between the TiO₂ layer and CH₃NH₃PbI₃ layer, which was synthesized via a low-pressure vapor assisted solution process. Both the fullerene and TiO₂ layers acted as electron collection layers together. The results show that the electron collection bilayer dramatically enhances cell performance even with part of the fullerene dissolved in DMF solution. The optimized PSC can achieve a PCE of 16.58%, with a FF of 75.91% measured under reverse voltage scanning. For PSCs only using TiO₂ as the collection layer, the average PCE and FF values are 10.2% and 58.6%, respectively. When fullerene was used as a single electron collection layer, the PCE is only 4.29%, because of the incomplete coverage of fullerene on the FTO substrate. Additionally, PSCs with fullerene interface layers showed far less hysteresis than reference cells without fullerene layers. Analysis of the equivalent circuit of devices and fluorescence lifetime measurements focusing on the CH₃NH₃PbI₃ film with an electron extraction layer confirm that in our device configuration fullerene facilitates electron injection from CH₃NH₃PbI₃ into the compact TiO₂ layer.