| 학회 | 한국재료학회 |
| 학술대회 | 2013년 봄 (05/23 ~ 05/24, 여수 엠블호텔(THE MVL)) |
| 권호 | 19권 1호 |
| 발표분야 | 제24회 신소재 심포지엄-The 2nd International Symposium on Green Energy 2013 |
| 제목 | Interface engineering in the Cd-free Cu(In,Ga)Se2 solar cells |
| 초록 | The hetero junction thin-film Cu(In,Ga)Se2 (CIGS) solar cells are promising PV systems for large-scale commercialization due to high conversion efficiency exceeding 20 %. The development of Cd-free materials for the buffer layer application and the optimization of the electronic band structure at the window/buffer/CIGS interfaces are key issues for increasing of the cell efficiency. However, the progress in Cd-free CIGS technology is much slow because of lack of basic science details. The experimental aproach was developed for analyzing the electronic structure of hetero interfaces by using UPS and XPS depth profile and optical measurements. By this aproach the energy band alighnment at the interfaces can be quantified. This is a critical parameter for electron transport in solar cells. The aproach was applied for two hetero interfaces ZnS/CIGS and Zn1-xMgxO /CIGS. The main research result is the quantification of the conduction band offsets at the ZnS/CIGS interface. For the first time UPS depth profile measurements were applied to assess the valence band structure of the ZnS/CIGS hetero-interface, as it exists in the real CIGS device. For the first time a small conduction band offset at the ZnS/CIGS interface was experimentally determined. The conduction band spike of 0.25 eV is consistent with the efficiency range of 18-18.6%, which is achieved by ZnS/CIGS solar cells. It was shown that the device efficiency can be enhanced if the energy barrier at interface is lowered further. Firstly, the ZnS bandgap should be reduced by controlling of the chemical composition (e.g. by heat treatment). Secondly, the surface band gap of the CIGS absorber should be widened by sulfurization or Ga doping. The same approach was applied to Zn1-xMgxO buffer and we were able to enhance the device efficiency above 16% by controlling the Zn1-xMgxO composition. The flat and cliff (-0.23 eV) conduction band alignments at the Zn0.8Mg0.2O/Cu(In0.7Ga0.3)Se2 and Zn0.9Mg0.1O/Cu(In0.7Ga0.3)Se2 interfaces were determined, respectively. The experimental results suggest that the bandgap energy of Zn1-xMgxO films is main factor that impact to the conduction band offset at the Zn1-xMgxO/Cu(In0.7Ga0.3)Se2 interface. Our study clearly demonstrated that designing the electronic structures at the heterointerfaces is an effective scientific approach to increase the conversion efficiency of thin-film solar cells. |
| 저자 | Larina Liudmila1, Chang-Soo Lee2 |
| 소속 | 1Institute of Biochemical Physics, 2Russian Academy of Sciences |
| 키워드 | Cu(In; Ga)Se2; solar cell; UPS and XPS depth profile; energy band alighnment |
