Study on efficiency improvement of multi-crystalline silicon solar cell by removing by-product and plasma induced damage generated during reactive ion etching

Abstract

Silicon solar cell texturing is the process of reducing the light reflection of the solar cells by changing their surface structure. Given that multi-crystalline silicon (mc-Si) wafers have grains with different orientations, their texturing process is more difficult to realize compared with those of monocrystalline silicon (mono-Si) wafers. There are two types of texturing processes: wet and dry texturing. Acidic solution-based wet-textured mc-Si samples have higher reflectance values than mono-Si wafers. However, the reactive ion etching (RIE)-texturing of mc-Si wafers has the advantage of decreasing reflectance to values below 10%. Despite this decrease in reflectance, RIE byproducts and plasma-induced damage bring about recombination that results in a decrease the passivation properties of the solar cell. In this study, the RIE byproducts as well as the plasma-induced damage of the RIE-textured mc-Si wafers were analyzed using SEM, STEM, and EDS analysis, while quasi-steady-state photoconductance (QSSPC) was used to confirm the optical characteristics of the RIE-textured mc-Si wafers. Additionally, HF treatment resulted in byproduct removal, and a relatively high implied Voc (673 mV) was confirmed within 3 min of HF treatment. The defect removal etching (DRE) process using KOH was applied to remove the lattice defect layer, and after 40 s of the DRE treatment, the implied Voc increased to 680 mV. Thus, the RIE-textured mc-Si solar cell showed a power conversion efficiency of 19.6%, which was 0.6% higher than that of acid-textured mc-Si solar cells based on the increase in short-circuit current (Isc).