Systematic investigation of metal dopants and mechanism for the SnO2 electron transport layer in perovskite solar cells

SnO2, the most promising alternative to TiO2 as the electron transport layer (ETL), has attracted great attention for perovskite solar cells (PSCs) due to its high bulk electron mobility, good band energy at the ETL/perovskite interface, and high chemical stability. To enable more efficient carrier transfer and extraction, elemental doping with different metal cations has been studied in SnO2 ETLs. However, the systematic investigation of the doping mechanism lag far behind their efficiency promotion. In this paper, elements of the same main group (Li, Na, K) and period (K, Ca, Ga) have been selected for doping in SnO2. The results showed that among the properties of the dopants, the electronegativity has the greatest influence. The smaller the electronegativity of the doping species, the more conducive it is to carrier transmission and separation. The corresponding mechanism was proposed and discussed. At last, an efficiency of 20.92% of PSCs based on SnO2–K was achieved. In addition, the doped SnO2 is more beneficial for the growth of perovskite crystals, thus reducing grain boundaries and enhancing the stability of the device.