Synergistic effect of alkali metal doping and thiocyanate passivation in CsPbBr3 for HTM-free all-inorganic perovskite solar cells

Abstract

All-inorganic CsPbBr₃ perovskite solar cells (PSCs) without hole-transport materials (HTMs) have attracted widespread attention because of their significant environmental stability. However, the poor quality of perovskite film and the energetics mismatch between CsPbBr₃ and charge-transport layers limit the further improvement of the CsPbBr₃ PSC performance. To solve this issue, the synergistic effect of alkali metal doping and thiocyanate passivation in NaSCN and KSCN dopants is utilized to improve the properties of the CsPbBr₃ film. The Na⁺ and K⁺ with smaller ionic radii are doped at the A-site of CsPbBr₃ to cause a lattice contraction, which contributes to the formation of CsPbBr₃ film with enhanced grain size and crystallinity. The SCN⁻ exerts the function of passivating the uncoordinated Pb²⁺ defects of CsPbBr₃ film, leading to a reduction of trap state density. The incorporation of NaSCN and KSCN dopants also adjusts the band structure of CsPbBr₃ film to improve the interfacial energetics match of the device. As a result, the charge recombination is suppressed, and the charge transfer and extraction are effectively promoted, delivering a highly enhanced power conversion efficiency of 10.38% for the champion KSCN doped CsPbBr₃ PSCs without HTMs compared to 6.72% efficiency for the original device. Moreover, the stability of the unencapsulated PSCs under ambient conditions with high humidity (85% RH, 25 °C) is distinctly improved, retaining 91.1% of the initial efficiency after 30 days of aging.