Researchers at CAS (Chinese Academy of Sciences) and Henan University have developed a nanomaterial-regulated doping strategy to pre-oxidize spiro-OMeTAD into radicals in the precursor solution with tin sulfoxide (SnSO) nanomaterials prepared at high temperature. The team increased the photoelectric conversion efficiency (PCE) of perovskite solar cells (PSCs) to 24.5% using the inorganic SnSO as a dopant to oxidize and regulate the organic hole transport layer 2,2′,7,7′-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9-spirobifluorene (spiro-OMeTAD).
Spiro-OMeTAD is an important hole transport layer (HTL) material. To enhance the charge transport capability of spiro-OMeTAD, lithium trifluoromethanesulfonyl imide (Li-TFSI) is required to mediate the reaction between oxygen and spiro-OMeTAD. However, this traditional doping method has low doping efficiency, and excessive Li-TFSI will remain in the spiro-OMeTAD film, leading to a decrease in the compactness and long-term conductivity of the film. The duration of the oxidation reaction usually takes 10 to 24 hours to reach the desired conductivity and work function. In this study, the researchers developed a fast and reproducible strategy to control the oxidation of the nanomaterial. They used SnSO nanomaterial to pre-oxidize spiro-OMeTAD to spiro-OMeTAD+TFSI- free radicals in precursor solutions. This improved the conductivity, optimized the energy level position of HTL, and achieved a high PCE of 24.5%.
The scientists found that the SnSO-regulated spiro-OMeTAD HTL has a pinhole-free, uniform, and smooth morphology. Both its performance and morphology remain stable even under high temperature and high humidity conditions.
"In addition, the oxidation process takes only a few hours, which is good for improving the commercial preparation efficiency of PSCs," said Prof. Chen Chong.
This study provides an effective strategy to further improve the efficiency and stability of PSCs, which is of great significance for promoting their commercialization.