A new simple route to grow Cu(In,Ga)Se2 thin films with large grains in the co-evaporation process |
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Affiliation: | 1. Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daejeon 34141, South Korea;2. Photovoltaic Team, Korea Institute of Energy Research, Daejeon 34129, South Korea |
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Abstract: | In the conventional three-stage co-evaporation process to grow Cu(In,Ga)Se2 (CIGS) film, a large grain is achieved by the co-evaporation of Cu and Se on (In,Ga)2Se3 layer at 550 °C in the second stage and then a p-type is achieved by the co-evaporation of In, Ga, and Se in the third-stage. We reported a new process where a CIGS film with a large gain and p-type is achieved by evaporation of Cu only in the second stage at 400 °C and by the Se annealing in the third stage. In the new process, thermal budget was lowered and the third-stage co-evaporation process was eliminated. It was found that the CIGS gain size increased when the Cu/(In + Ga) ratio was above 0.7 and an addition thin CIGS layer appeared on the CIGS surface. The reaction path with Cu was described in the Cu-In-Se ternary phase diagram. The cell conversion efficiency increased from 9.6 to 15.4% as the Se annealing temperature increased from 400 to 550 °C in the third stage, mainly due to the increase of open-circuit voltage and fill factor. Our process demonstrated a new route to grow a CIGS film with a less thermal budget and simpler process in the co-evaporation process. |
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Keywords: | CIGS solar cells Co-evaporation process New route Low temperature Cu evaporation Se annealing |
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