Black Mc-Si Prepared By Metal Catalysis Chemical Etching And Its Solar Cells

Black silicon is a novel semiconductor of light trapping nanostructure, usually hasextremely low reflectance in visible light. It has attracted increasing attention from manyresearchers in recent years for the great potential in silicon-based solar cells. However, it isstill far away from the industry-scale application due to the following facts: the most oftechniques are still under studying in laboratory; the power conversion efficiency is lowerthan the industry level; few of promising techniques (i.e. plasma dry etching) requiresexpensive and complicate equipments, and faces many challenges to satisfy industrydemands for solar cells. From the point of view of industrialization, black silicon solarcells must improve its power conversion efficiency and reduce its cost. As a dominantproduction among Si-based solar cells, the multi-crystalline silicon (mc-Si) solar cellssuffered more light reflection loss than that of single-crystalline silicon. Therefore, it willbe extreme important to explore a technique in achieving the high efficient black mc-Sisolar cells.In this work, we will study a metal-catalyzed chemical etching (MCCE) technique,which is cost-effective and more applicable to the existing production line technology formc-Si solar cells. A new micro-nano composite texture formed in the surface of solar cellswill reduce the reflectivity thus improve its power conversion efficiency. The main resultsincluded:First, the MCCE technique was studied systematically. Several chemical solutionswere composed: the etching solution consisting of AgNO3, HF and H2O2, is able tofabricate Si nanostructure in pores or wires in very short time; the clean solution canremove the remain Ag particles sunk in the nanostructure; the post etching solution willmanipulate the shape and surface area of the nanostructure. Therefore, above solutionswere optimized to form various nanostructures on the surface of mc-Si wafers.Second, an approach to form micron-nano composite texture formed in the surface ofsolar cells was investigated. Usually, the routine acid texture process used in productionline will result in a micron texture and~25%reflection. An additional MCCE step will generate a nano texture to the former micro texture. In fact, a single nano texture of a deptharound400nm could lead to very low reflection but large surface area, which will act assurface recombination centers of photogenerated electron-hole pairs and depress theefficiency of solar cell. With the configuration of micron-nano composite texture, ashallow nano texture could result in a moderately low reflection (5-15%) in mc-Si solarcell, thus reduce the surface recombination.Third, several batches of black mc-Si solar cells have been fabricated on an industrialproduction line at Canadian Solar Inc.@Suzhou. Except the texture process, otherprocesses such as diffusion, SiN_x-PECVD and screen printing are same as that used in theline. After each batch, the efficiency, the reflection, the minor carrier lifetime,microstructure and etc. have been measured as well as the relationship among them wascarefully investigated. Based on those results, some parameters were updated in next batchfor better performance of solar cell. Our experimental showed that the nano texture hasvital influence to the final efficiency of solar cells. An average17.5%efficiency achievedin one batch (300pieces) with few cells reach to18%efficiency, is higher than thataverage17.2%efficiency in the regular production line. Such improvement can be ascribedto the improvement of light absorption in black mc-Si solar cells, and to the post-etched Sinanostructure, which is much suitable for the following diffusion process to form good pnjunction and for the effective passivation of SiN_xfilm.In summary, the MCCE method has been verified in both laboratory and industryproduction line, while the physical mechanism of the role micron-nano composite textureon the efficiency of solar cell was expounded. The presented results and methods havegreat impacts to the fundamental research and application of photovoltaic community, andwe believe in the black mc-Si solar cell has bright application in the future.