Prediction of sub-pyramid texturing as the next step towards high efficiency silicon heterojunction solar cells

Abstract Over the past few decades, silicon-based solar cells have dominated the photovoltaic industry, and the interfacial morphology of crystalline silicon/amorphous silicon (c-Si/a-Si) is a key success factor to approach the theoretical efficiency of Si-based solar cells, especially Si heterojunction (SHJ) technology. One of the major issues plaguing the SHJ development, is the unexpected c-Si epitaxial growth and nanotwins formation at c-Si/a-Si interface. By a combination of atomic-resolution high-angle annular dark field scanning transmission electron microscope (HAADF-STEM) images and in-situ high resolution transmission electron microscope (HRTEM), we obtained new finding in high-efficiency SHJ industrial devices, and simulated c-Si/a-Si interfacial morphology. Employing microsecond-long low-temperature (500 K) molecular dynamic simulations, we proposed a new strategy to prevent from both c-Si epitaxial growth and nanotwin formation, that the texture should have a decreased pyramid apex-angle (slightly smaller than 70.53°) in SHJ solar cells. The new apex-angle consists of hybrid (111)0.9/(011)0.1 c-Si planes, rather than pure (111) planes in conventional texture pyramid. The nature of the hybrid c-Si plane is low-energy c-Si/a-Si interface, which is unfavorable for either epitaxial c-Si growth or nanotwins formation. More importantly, given there is not any additional industrial preparation process, the new design of hybrid c-Si plane could improve c-Si/a-Si interfacial morphology for a-Si passivated contacts technique, and wide-applied for all silicon-based (single-junction and tandem) solar cells as well.