Towards a cutting-edge metallization process for silicon heterojunction solar cells with very low silver laydown

Abstract

Within this work, we investigate the potential to optimize the screen-printed front side metallization of silicon heterojunction (SHJ) solar cells. Three iterative experiments are conducted to evaluate the impact of the utilized fine mesh screen configurations and grid layout adaption (finger pitch) for the front side metallization on silver laydown and electrical performance of the solar cells. With respect to the screen configuration, we compare the performance of a fine-mesh knotless screen to a conventionally angled screen demonstrating an additional gain of Δη = +0.1%_abs due to reduced shading losses. Additionally, a grid layout is improved by increasing the number of contact fingers from 120 to 156. Furthermore, the current possibility to push the fine-line printing process for low-temperature pastes to the limit is investigated by reducing the nominal finger width w_n to 20, 18, and 15 μm. It is shown that even the smallest nominal width of w_n = 15 μm can be printed with high quality, leading to an additional efficiency gain of Δη = +0.15%_abs as well as a reduction of silver paste laydown by −5 mg. Finally, a batch of champion cells is fabricated by applying the findings of the previous experiments, which results in a maximum efficiency of η_max = 23.2%. Compared to the reference group without optimization, this corresponds to a gain of Δη = +0.17%_abs, which comes along with an additional decrease of the silver paste laydown by approximately −2 mg. This emphasizes the significance of consistent optimization of the screen-printing process in terms of cell performance and resource utilization for SHJ solar cells.