High Vapor Transport Deposition: A Novel Process to Develop Cu2ZnSn(SxSe1–x)4 Thin Film Solar Cells

Kesterite thin film solar cells are known to be a promising cost‐effective solution because they are based on earth‐abundant and environmental compounds. However, it is known that their best efficiency (12.6%) has not been improved since 2013, meanwhile other thin‐film solar cells have demonstrated that their performance has been enhanced continuously. The main drawbacks to explain this situation is the narrow process window of this compound and simultaneously, the high composition and thermal control needed to avoid intrinsic defects in the p‐type layer. The high vapor transport deposition process has not been explored yet by kesterite thin film solar cell developers. Herein, we present the results obtained using a design of a new vacuum deposition method similar to close space sublimation, which reported excellent results in CdTe. The main advantages of this novel process are: 1) to achieve a high deposition rate; 2) to be able to deposit precursor materials and to carry out the sulfur‐selenization in the same process chamber, avoiding the two steps used in the sequential process; 3) to provide a high accuracy in the chemical composition control; and 4) simple design using commercial components to facilitate its scalability for large production. The process called high vapor transport deposition is applied for the first time to deposit kesterite absorber films. The main advantage of this process is the fine tuning capabilities to control the desired stoichiometry in the absorber layer. Additionally, the process allows a high deposition rate and low temperature in the evaporation cells where raw materials are placed.