Improved Surface Passivation by Wet Texturing, Ozone-Based Cleaning, and Plasma-Enhanced Chemical Vapor Deposition Processes for High-Efficiency Silicon Heterojunction Solar Cells

Silicon heterojunction (SHJ) solar cells rely on excellent surface passivation of the crystalline wafer. This article reports on the development of wet chemical processes varying the texturing and optimizations of the final clean processes for Czochralski-silicon wafers used in SHJ solar cells. Three different additives are used to modify both the pyramid size and the texture homogeneity on the wafers. As an alternative to standard Radio Corporation of America (RCA) sequence, ozonized deionized (DI) water-based procedures are used to clean the silicon surfaces, reducing process time and the amount of chemicals to obtain the same cleaning quality. In addition, two different amorphous silicon (a-Si:H) passivation stacks are discussed in this article demonstrating an improvement in the open-circuit voltage, V-oc, by 15 mV. Combining these wet chemistry improvements with optimized process conditions for the passivating a-Si:H layers deposited by plasma-enhanced chemical vapor deposition (PECVD), allows to obtain high-efficiency devices both in small- and full-area solar cells. On 6 in. full-area solar cells (215.3 cm(2) aperture area), open-circuit voltages, fill factors, and efficiency values of 738 mV, 81.4%, and 23.2% are obtained, respectively; for 4 cm(2) cell size, the best obtained values in equivalent devices are 741 mV, 80.6%, and 23.2%.