On Electrical Properties of Black Silicon for Photovoltaic Applications

Silicon solar cells are the leading force in the photovoltaics market due to their low mass-production costs and wide range of application scenarios. Enhancement of optical generation and reduction of recombination loss are two important aspects of high-efficiency solar cell development. Black silicon (b-Si) texturing, one of the most effective light-trapping techniques, has received considerable attention for solar cell applications. However, the development of high-efficiency b-Si solar cells is significantly hindered by a lack of in-depth understanding of the electrical properties of b-Si textures. It is widely observed that the inferior electrical performance of a b-Si emitter outweighs the gain in optical performance, resulting in lower efficiencies. However, it is also found that the surface recombination loss of a passivated b-Si texture can be unexpectedly low, which could contribute to high efficiency for some solar cell architectures. This thesis aims to determine (1) how b-Si surface morphology should be optimized to achieve high performance solar cells and (2) whether b-Si textures are indeed better than conventional textures. This thesis first provides a literature review of solar cell surface texturing techniques with an emphasis on b-Si texturing. The primary research approaches of this thesis are then shown. A systematic investigation of b-Si field-effect passivation enhancement is presented, exploring the root cause of the low surface recombination loss for undiffused b-Si surfaces and determining the optimal combinations of surface passivation schemes and b-Si morphologies. Significant field-effect passivation enhancement is found when the surface charge density is moderate, and the enhancement strength increases as the distance between the opposite surfaces decreases. Next, a fundamental study of POCl3-diffused b-Si emitters with various textures is presented, covering dopant distribution characteristics, emitter lateral conductance behaviour, and recombination loss mechanisms. Optimization ...