Abstract
Multi-junction solar cells are considered for various applications, as they tackle various loss mechanisms for single junction solar cells. These losses include thermalization and non-absorption below the band gap. In this work, a tandem configuration comprising copper-indium-gallium-di-selenide (CIGS) and hydrogenated amorphous silicon (a-Si:H) absorber layers is studied. Two main challenges are addressed in this work. Firstly, the natural roughness of CIGS is unfavorable for monolithically growing a high quality a-Si:H top cell. Some sharp textures in the CIGS induce shunts in the a-Si:H top junction, limiting the electrical performance of such a configuration. To smoothen this interface, the possibility of mechanically polishing the intermediate i-ZnO layer has been explored. The second challenge that is addressed, is the significant current mismatch in these tandem architectures. To enhance absorption in the current-limiting top cell, the ZnO:Al front electrode was textured by means of wet-etching the entire tandem stack. We demonstrated that one can manipulate the morphology of the random textures by varying the growth conditions of the ZnO:Al, leading to better light management in these devices.
Highlights
Thin-film technologies can have certain attractive characteristics in terms of weight, shapes, and possible translucence
The challenge for two-terminal devices is to accomplish a design in which top cell and bottom cell are close to current matching while preserving a high value for the fill factor (FF)
We demonstrate two approaches to tackle the above limitations to improve the performance of amorphous silicon (a-Si):H/CIGS tandem device
Summary
Thin-film technologies can have certain attractive characteristics in terms of weight, shapes, and possible translucence. In search for higher voltages and efficiencies, much research has focused on multi-junction thin-film photovoltaic devices. This is not limited to the field comprising III-V semiconductors, and thin-film technology materials have been extensively researched. In the field of CIGS such stacks have been proposed, including combining this junction with various dye sensitized solar cells [9,10,11]. In this latter field, an additional incentive is to limit the use of the relatively scarce Indium. Two-terminal configurations face the biggest challenges in the design and fabrication of the cells
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