Abstract
Increasing the efficiency of solar cells relies on light management. This becomes increasingly important for thin-film technologies, but it is also relevant for poorly absorbing semiconductors like silicon. Exemplarily, the performance of a-Si:H/µc-Si:H tandem solar cells strongly depends on the texture of the front and rear contact surfaces. The rear contact interface texture usually results from the front surface texture and the subsequent absorber growth. A well-textured front contact facilitates light-coupling to the solar cell and light-trapping within the device. A variety of differently textured ZnO:Al front contacts were sputter deposited and subsequently texture etched. The optical performance of a-Si:H/µc-Si:H tandem solar cells were evaluated regarding the two effects: light-coupling and light-trapping. A connection between the front contact texture and the two optical effects is demonstrated, specifically, it is shown that both are induced by different texture properties. These findings can be transferred to any solar cell technologies, like copper indium gallium selenide (CIGS) or perovskites, where light management and modifications of surface textures by subsequent film growth have to be considered. A modulated surface texture of the ZnO:Al front contact was realized using two etching steps. Improved light-coupling and light-trapping in silicon thin-film solar cells lead to 12.5% efficiency.
Highlights
Transparent conductive oxides (TCOs) play an important role as contact materials in solar cells [1,2].The front contacts simultaneously fulfill numerous requirements: high transparency, high conductivity, and in some cases exhibit a surface texture that facilitates a good optical performance of the solar cell.Many publications have already addressed the importance of balancing the transparency to reduce absorption losses and the electrical properties of TCO films in thin-film solar cells [3,4,5,6]
While most studies focus on silicon thin film solar cells, light management has been studied in copper indium gallium selenide (CIGS) and metal halide perovskite technology as well [13,14,15,16]
As a well-established example, we demonstrate these by other thin film technologies, the analysis of light-coupling and -trapping is of general interest and effects be in considered a-Si:H/μc-Si:H
Summary
Transparent conductive oxides (TCOs) play an important role as contact materials in solar cells [1,2].The front contacts simultaneously fulfill numerous requirements: high transparency, high conductivity, and in some cases exhibit a surface texture that facilitates a good optical performance of the solar cell.Many publications have already addressed the importance of balancing the transparency to reduce absorption losses and the electrical properties of TCO films in thin-film solar cells [3,4,5,6]. The front contacts simultaneously fulfill numerous requirements: high transparency, high conductivity, and in some cases exhibit a surface texture that facilitates a good optical performance of the solar cell. While most studies focus on silicon thin film solar cells, light management has been studied in copper indium gallium selenide (CIGS) and metal halide perovskite technology as well [13,14,15,16]. The majority of these publications refer to the necessity of good light-trapping in the device to foster the absorption of the otherwise weakly absorbed red portion of the solar spectrum. The pathway enhancement [18] is of special importance for the wavelength range that
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