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Cu(In,Ga)Se2 Solar Cells with Amorphous In2O3-Based Front Contact Layers
Takashi Koida1, Yuko Ueno1, Jiro Nishinaga1
1Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology , 1-1-1 Umezono, Tsukuba 305-8568, Japan.
ACS Applied Materials & Interfaces
|August 23, 2017
Summary
Amorphous indium oxide-based front contacts enhance copper indium gallium selenide solar cells by improving current while maintaining voltage and fill factor. These novel transparent conducting and semiconductor layers offer superior performance over traditional materials.
Area of Science:
- Materials Science
- Renewable Energy
- Semiconductor Physics
Background:
- Copper indium gallium selenide (Cu(In,Ga)Se2 or CIGS) solar cells are a promising photovoltaic technology.
- Transparent conducting oxide (TCO) and transparent oxide semiconductor (TOS) layers are critical for CIGS solar cell performance.
- Traditional zinc oxide (ZnO)-based layers often suffer from grain boundary issues affecting electron mobility.
Purpose of the Study:
- To investigate the effectiveness of amorphous indium oxide (In2O3)-based front contact layers in CIGS solar cells.
- To enhance short-circuit current density (Jsc) while maintaining high fill factor (FF) and open-circuit voltage (Voc).
- To explore the role of amorphous indium gallium zinc oxide (a-In-Ga-Zn-O) as a TOS layer.
Main Methods:
- Fabrication of CIGS solar cells with a glass/Mo/CIGS/CdS/TOS/TCO structure.
- Introduction of n-type amorphous indium gallium zinc oxide (a-In-Ga-Zn-O) as the TOS layer.
- Characterization of electrical properties, including carrier density (N) and electron mobility, of the amorphous layers.
- Comparison of amorphous indium oxide-based layers with conventional ZnO:Al layers.
Main Results:
- Amorphous In2O3-based front contacts significantly enhanced Jsc in CIGS solar cells.
- Amorphous In-Ga-Zn-O layers, free of grain boundaries, exhibited high electron mobility and controlled carrier density (N from 2 × 10^15 to 3 × 10^18 cm^-3).
- High FF and Voc were maintained across a broad range of N values.
- Amorphous In2O3:H and a-In-Zn-O layers showed higher electron mobilities than conventional ZnO:Al TCO layers.
- In2O3-based layers had lower free carrier absorption with comparable sheet resistance to ZnO:Al.
Conclusions:
- Amorphous In2O3-based front contact layers are effective for improving CIGS solar cell performance, particularly Jsc.
- The grain-boundary-free amorphous structure of a-In-Ga-Zn-O enables superior electronic properties for TOS applications.
- Controlling series resistance within the TOS layer mitigates FF and Voc decrease due to electronic inhomogeneity.
