Cs-Doped TiO2 Nanorod Array Enhances Electron Injection and Transport in Carbon-Based CsPbI3 Perovskite Solar Cells

Carbon-based CsPbI3 perovskite solar cells (CsPbI3 C-PSCs) without hole-transporting materials have been attracting much attention because of their high stability. However, the electron transport layer (ETL) of TiO2 mesoporous scaffolds has hindered electron transport. Herein, we solve the above problem by employing a Cs-doped TiO2 (Cs-TiO2) nanorod array as an ETL, which provides a direct and fast electron path. Cs doping well increases the free charge carrier density in the TiO2 nanorod array to enhance the electron transport. Besides, electron injection is accelerated because of the upshift of conduction band levels and the improvement in the pore-filling of the perovskite layer. Consequently, CsPbI3 C-PSCs based on Cs-TiO2 nanorod arrays achieved a significantly higher power conversion efficiency (PCE) of 9.5%, compared to the devices based on TiO2 nanorod arrays (5.8%). Furthermore, the nonencapsulated devices based on Cs-TiO2 nanorod arrays show almost no PCE degradation after 3000 h of storage in ambient air (20-30% relative humidity, 20-30 degrees C).