Natrium Doping Pushes the Efficiency of Carbon-Based CsPbI Perovskite Solar Cells to 10.7.

The CsPbI inorganic perovskite is a potential candidate for fabricating long-term operational photovoltaic devices owing to its intrinsic superb thermal stability. However, the carbon-based CsPbI perovskite solar cells (C-PSCs) without hole transport material (HTM) are currently disadvantaged by their relatively low power conversion efficiency resulting from the poor grain quality and mismatched energy band levels of the as-made CsPbI films. Herein we demonstrate that by doping Na into the CsPbI lattice, the grain quality is significantly improved with low defect density, and also, the energy band levels are better matched to the contact electrodes, affording a higher built-in potential. Consequently, the V of the C-PSCs is drastically increased from 0.77 to 0.92 V, and the efficiency from 8.6% to 10.7%, a record value for the CsPbI PSCs without HTM. Moreover, the non-encapsulated device showed virtually no performance degradation after 70 days of storage in air atmosphere.