| AVS 58th Annual International Symposium and Exhibition | |
| Energy Frontiers Focus Topic | Thursday Sessions |
| Session EN-ThP |
| Session: | Energy Frontiers Poster Session |
| Presenter: | Tadatsugu Minami, Kanazawa Institute of Technology, Japan |
| Authors: | T. Minami, Kanazawa Institute of Technology, Japan T. Miyata, Kanazawa Institute of Technology, Japan Y. Nishi, Kanazawa Institute of Technology, Japan J. Nomoto, Kanazawa Institute of Technology, Japan |
| Correspondent: | Click to Email |
The effect of inserting a thin-film buffer layer on the obtainable efficiency in n-ZnO/p-Cu2O heterojunction solar cells was investigated with a transparent conducting Al-doped ZnO (AZO) thin film/Cu2O sheet structure. To improve conversion efficiency, various heterojunction solar cells were fabricated by forming an AZO/thin-film buffer layer/Cu2O structure on the front surface of thermally oxidized Cu2O sheets that function as the active layer as well as the substrate. It was found that achieving higher efficiency Cu2O-based heterojunction solar cells fabricated by depositing various thin films on Cu O sheets requires that the surface of the Cu2O sheets always be treated using a low-damage deposition technology at a low deposition temperature .
The Cu2O sheets, with electrical properties such as resistivity on the order of 103 Ωcm, hole concentration on the order of 1013 cm-3 and Hall mobility above 100 cm2/Vs, were prepared by a thermal oxidization of copper sheets under appropriate conditions. The AZO thin film and the thin-film buffer layer were prepared by a pulsed laser deposition (PLD) using an ArF excimer laser. As an example of AZO/buffer layer/Cu2O heterojunction solar cells, AZO/ non-doped ZnO (ZO)/Cu2O solar cells were fabricated by inserting a ZO thin film as the buffer layer. It was found that the obtainable conversion efficiency in AZO/ZO/Cu2O heterojunction solar cells increased markedly as the deposition temperature of the AZO and ZO thin films was decreased from approximately 300oC to room temperature (RT) , i.e., non-intentionally heated Cu2O sheets. In addition, when the ZO thin films were prepared on non-intentionally heated Cu2O sheets by PLD, the efficiency (η) increased considerably as the introduced O2 gas pressure was increased; η, approximately 3 % with a ZO thin-film layer deposition at an O gas pressure of 0.1 Pa, gradually increased as the O2 gas pressure was increased up to approximately 1.2 Pa, and then decreased markedly at a pressure of approximately 1.5 Pa. The optimal thickness of the ZO thin-film layer was in the range from 30 to 50 nm. The obtained increase of η as the ZO film thickness was increased up to approximately 50 nm may be attributable to an improvement of film quality; in contrast, the decrease of η as the ZO film thickness was increased above approximately 50 nm may be attributable to the short lifetime of minority carriers in the n-ZO thin film. An AZO/ZO/Cu2O heterojunction solar cell fabricated under optimal preparation conditions exhibited an efficiency of 3.83% under simulated AM1.5G solar.