Optimization Of Substrate’ Light Trapping For Heterojunction Silicon Solar Cell And Its’application

Silicon heterojunction(SHJ) solar cell consisting of a hydrogenated amorphous silicon(a-Si:H) film deposited on crystalline silicon wafer(c-Si) has drawn considerable attention of the photovoltaic industry due to its high efficiency, high stability, low cost and low temperature fabrication.Texturing increases light-absorption area and reduces the re?ectivity of solar cell surfaces, thereby leading to an increase in short circuit current density(Jsc). However, for SHJ solar cell, optical efficiency gains are often achieved at the detriment of electrical performance because the silicon surface is a part of the junction of the device.For industrial fabrication of textured wafers, a method based on the NaOH and isopropyl alcohol(IPA) is widely used because of its low cost and high technical maturity. However,a drawback of this approach is contamination due to Na+ ions, which decreases carrier lifetime and degenerates the performance of photovoltaic devices.Metallic contamination can be avoided by acid-based chemical polish etching(CPE), but the CPE solution contains toxic chemicals such as HNO3 and HF, making the process lengthy and hazardous.Etching with tetramethylammonium hydroxide(TMAH) is attractive because it is non-toxic, it can be easily disposed of, and it does not cause ion contamination but still ensures good anisotropic etching.In this study, therefore, the texturing process was adjusted with the aim of optimizing the three parameters, namely, the optical properties, electrical characteristics, and surface morphology, of the silicon wafers to find out the suitable substrates for the SHJ solar cell. The main contents include:(1)The solution of acid or alkaid was used for etching the original wafers to remove the saw damages, pyramids were then formed on the damage-free silicon wafer surface employing the same texturing conditions.This section focuses mainly on the research of original wafer morphology on the texturing and passivation.(2)TMAH texturing conditions(TMAH concentration, temperature range, IPA concentrations, etching time) are varied to optimize the surface morphology of silicon wafers and the light trapping effect. In comparison with NaOH texturing, the TMAH process described here yields smaller pyramids with smoother(111) facets, leading to improved performance of silicon heterojunction solar cells, with a conversion efficiency from 14..4% to 17.8%.(3)According to the optimal result of the pyramidal morphology, the metal assigned chemical etching(MACE) was introduced to fabricate hierarchical structure combing pyramids and silicon nanowires(SiNWs). The hierarchical structure can enhance the light trappping of substrates. This chapter mainly analyses the influence of different MACE etching time on the structures and the application on the SHJ solar cell.