The modification of gallium and band-gap in-depth distribution in the Cu(In,Ga)Se2 thin film solar cells by selenization processes

• Main Authors: Chi, Kang-Ting, 紀岡廷
• Other Authors: Shieh, Han-Ping
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/97700696199803516354

碩士 === 國立交通大學 === 光電工程研究所 === 102 === Cu(In,Ga)Se2 (CIGSe) is a potential material for developing high efficiency thin film solar cells. In the selenization processes, gallium (Ga) accumulates near the back-side region of CIGSe absorber, resulting in low open-circuit voltage (VOC) and conversion efficiency. This thesis investigates the effect of Ga distribution in each annealing step and optimizes the three step annealing process. Ga diffused to the CIGSe/Mo interface in the first-step annealing, and diffused to surface of CIGSe absorber in the third-step. The three-step annealing parameters, therefore, were optimized as the annealing temperatures of 350, 450, and 550oC for 30, 15, and 30 minutes, respectively. The Ga/(In+Ga) ratio is 0.15 by using the optimized three-step annealing parameters. However, the Ga concentration remains low near the surface region, and consequently results in high Ga concentration at the CIGSe/Mo interface. To improve this issue, a new double-stacked precursor structure was proposed in the thesis. This precursor structure not only enhances the VOC due to the increase of Ga content near the surface region of CIGSe absorber, but also increases the cell efficiency from 4.88 to 7.25%. The use of double-stacked precursor effectively enhances conversion efficiency in the selenization processes.