Variable Light Soaking Effect of Cu(In,Ga)Se 2 Solar Cells with Conduction Band Offset Control of Window/Cu(In,Ga)Se 2 L
- PDF / 108,184 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 77 Downloads / 175 Views
1012-Y07-03
Variable Light Soaking Effect of Cu(In,Ga)Se2 Solar Cells with Conduction Band Offset Control of Window/Cu(In,Ga)Se2 Layers Takashi Minemoto1, Yasuhiro Hashimoto2, Takuya Satoh2, Takayuki Negami2, and Hideyuki Takakura1 1 Photonics, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga, 525-8577, Japan 2 Matsushita Electric Ind. Co., Ltd., 3-4 Hikaridai, Seika-cho, Soraku-gun, Kyoto, 612-0237, Japan
ABSTRACT The impact of the conduction band offset (CBO) between window and Cu(In,Ga)Se2 (CIGS) layers on the light soaking (LS) effect in CIGS solar cells has been clarified with continuous CBO control using a (Zn,Mg)O (ZMO) window layer. Two types of CIGS solar cells with different window/buffer/absorber layers configurations were fabricated, i.e., ZMO/CIGS (without buffer layer) and ZMO/CdS/CIGS structures. Current-voltage (J-V) characteristics of the solar cells revealed that positive CBO values, where the conduction band of ZMO is higher than that of CIGS, higher than 0.16 eV induces J-V curve distortion, i.e., LS effect, and all the JV characteristics stabilized in 30 min. The degrees of the LS effect were dominated by the CBO value between ZMO and CIGS layers in the both structures regardless of the existence of CdS buffer layers. These results indicate that the LS effect is dominated by the highest barrier for photo-generated electrons in the conduction band diagram, i.e., the CBO between ZMO and CIGS layers, and quantitatively the LS effect emerges from the CBO value higher than 0.16 eV. INTRODUCTION Cu(In,Ga)Se2 (CIGS) solar cells are one of the most promising candidate for highefficiency and low-cost thin-film solar cells. While a conversion efficiency of the cells has approaching 20% [1], there still remain unclear current transportation mechanisms and device operations. One of the unclear operation mechanisms is light soaking (LS) effect [2-6]. The efficiency of CIGS solar cells are observed to improve after exposure to white light for typically 30 min, generally due to increases in fill factor (FF) and open-circuit voltage (Voc). The degree of the LS effect, i.e., a difference between initial to stabilized values, seems to be greater in CIGS solar cells with buffer/window layers such as ZnS [4], InS(O,OH) [5] and In(OH)3:Zn2+ [6] other than CdS. This would be due to the difference in band alignments of the devices, especially in the conduction band offset (CBO) between window and CIGS layers. In previous reports, we proposed a new window layer of (Zn,Mg)O (ZMO) which can continuously control the CBO value in the CIGS solar cells [7]. Also, we clarified the effect of the CBO value on the device performance and demonstrated the high efficiency CIGS solar cells without a CdS layer [8-11]. In the series of operation characterizations of these devices, we have found that there is clear difference in the LS effect in CIGS solar cells with different CBO values. In this paper, we report on the variable degree of the LS effect on the CIGS solar cells with the controlled CBO using the ZMO window laye
Data Loading...
