Researchers find new ways to regulate hole transport layer for efficient perovskite solar cells

According to a research published on Nano Energy recently,a group led by Prof. CHEN Chong from Hefei Institutes of Physical Science (HFIPS) of Chinese Academy of Sciences (CAS)successfully increased the photoelectric conversion efficiency (PCE) of perovskite solar cells (PSCs) to 24.5%.

They used inorganic nano-materials tin sulfoxide (SnSO) as a dopant to oxidize and regulate organic hole transport layer 2,2′,7,7′-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9-spirobifluorene (spiro-OMeTAD).

Spiro-OMeTAD is the most critical hole transport layer (HTL) material. To improve the charge transport ability 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. And the duration of the oxidation reaction usually takes 10-24 hours to reach the desired conductivity and work function.

In this research, scientists developed a fast and reproducible strategy to control the oxidation of nanomaterial. They used SnSO nanomaterial to pre-oxidize spiro-OMeTAD into spiro-OMeTAD^.+TFSI- free radicals in precursor solutions. This improved the conductivity, optimized the energy level position of HTL, and achieve a high PCE of 24.5%.

They found that spiro-OMeTAD HTL regulated by SnSO had a pinhole-free, uniform, and smooth morphology. Both its performance and morphology stayed stable even under high temperature and high humidity conditions.

"Also, the oxidation process only takes 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.

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