Tailoring Cu2CdSnS4 Phase Evolution for High-Efficiency Solar Cells via Precursor Engineering
Résumé
Copper‐based sulfide Cu2CdSnS4 solar cells exhibit excellent electronic band properties with the substitution of Cd with Zn in Cu2ZnSnS4 due to the reduction of sub‐band‐gap states. However, their performance remains inferior compared to other thin‐film solar cells, and the fundamental material characteristics that are responsible for this inferior performance are not elucidated. In this paper, the performance‐limiting factors of complicated chemical reactions involved in the sulfurization process are revealed by an in‐depth investigation of phase evolution and grain growth. It is shown that the Cu2‐xS in a Cl‐based precursor involved a multi‐step phase fusion reaction with the CdS and SnSx intermediate phases, leading to a severe VOC deficit. Conversely, it is observed that a rapid phase transition with the formation of Cu2SnS3 (CTS) at the initial stage for the Ac‐dominated sample generates numerous nucleation centers, resulting in poor crystallization. Hence, when a favorable ratio of Cl−/Ac− anion is employed, the substantial deficit in VOC of the CCTS solar cells primarily originated from [2CuCd++SnCd2−] defect cluster is alleviated, which is believed to result from the modified multi‐phase fusion and grain growth mechanism. The noteworthy champion efficiency of 11.89% with a VOC/VOC,SQ of 65.0% for the CCTS solar cells is achieved.