NaBr-Modified CsPbI₂Br Improves the Comprehensive Performance of the Solar Cells

Perovskite solar cells based on the CsPbI ₂ Br photoactive layer have received much attention recently because of the suitable bandgap and good thermal stability for CsPbI ₂ Br, as compared with other perovskite photoactive materials. However, the poor quality for the normally prepared CsPbI ₂ Br layers severely restricts realization of high performance for the related solar cells. Herein, we report a facile low-temperature solution process, in which NaBr is introduced into the CsPbI ₂ Br precursor solution as an additive, to prepare high-quality CsPbI ₂ Br layers with the improved crystallinity and reduced defect/trap density, as well as the reduced surface roughness and enhanced resistance to moisture and Ag diffusion. Thanks to the enhanced charge extraction, suppressed carrier recombination because of the improved CsPbI ₂ Br quality, the power conversion efficiency (PCE) of the corresponding solar cells has a remarkably increase to 14.70% compared with 13.26% for the control device with the pristine CsPbI ₂ Br layer. Moreover, the improved operation stability for the unencapsulated devices with the NaBr-modified CsPbI ₂ Br layers is observed, i.e., ∼90.1% retention of the initial PCE after 200 h aging in air with the relative humidity of 30%–40%, much more stabler than the control device.