Improvement of silicon heterojunction solar cell performance with new surface structure and wide band gap carrier selective layers

Dönerçark, Ergi
The photovoltaic (PV) industry is dominated by silicon-based solar cells owing to the abundance of silicon and its full-fledged technology. The main road for the PV industry points out to enhance the conversion efficiency of solar cells while decreasing production costs, which is crucial for improving renewable energy market share. The silicon heterojunction solar cells (SHJ) are receiving attention on this road map due to their higher conversion efficiencies, simple process flow, and low-temperature fabrication sequence. In order to further enhance the SHJ device performance, both electrical and optical properties should be improved simultaneously. In this Ph.D. thesis work, various aspects of SHJ solar cells, such as surface texturing, surface passivation, and material choices, were addressed. Firstly, surface texturing was studied to search for new approaches to reduce optical losses. Even though the well-established surface texturing method generating random pyramids on the surface reduces the reflection successfully, there is still room for improvement. A new and novel silicon surface texturing method based on copper-assisted chemical etching was developed for efficient light management on the surface. With this technique, tetragonal-star shaped inverted pyramids were formed, resulting in extremely low reflectance values. Secondly, the surface passivation of silicon was studied using different process conditions and material systems. The SHJ solar cell performance was significantly improved by understanding the chemical passivation kinetics and improving the surface passivation quality. Thirdly, wide band gap materials were integrated into the SHJ solar cell structure to decrease parasitic absorption losses. Furthermore, the free-carrier absorption losses were reduced significantly by tuning TCO's electrical and optical properties. Based on the theoretical and experimental explanations, the novel method for light trapping and integration of wide band gap materials to SHJ solar cell structure were shown to offer promising alternatives to existing technologies for future applications. With these new material systems and process improvements, we have achieved high-efficiency values of up to 21.2% in the SHJ solar cells fabricated at ODTÜ-GÜNAM.


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Citation Formats
E. Dönerçark, “Improvement of silicon heterojunction solar cell performance with new surface structure and wide band gap carrier selective layers,” Ph.D. - Doctoral Program, Middle East Technical University, 2021.