Coupling and Trapping of Light in Thin-Film Solar Cells Using Modulated Interface Textures

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/mu c-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/mu c-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.