Characterization and optimization of high-efficiency crystalline silicon solar cells: Impact of recombination in the space charge region and trap-assisted Auger exciton recombination

Since the photoconversion efficiency eta of the silicon-based solar cells (SCs) under laboratory conditions is approaching the theoretical fundamental limit, further improvement of their performance requires theoretical modeling and/or numerical simulation to optimize the SCs parameters and design. The existing numerical approaches to modeling and optimizing the key parameters of high-efficiency solar cells based on monocrystalline silicon, the dominant material in photovoltaics, are described. It is shown that, in addition to the four usually considered recombination processes, namely, Shockley-Read-Hall, surface, radiative, and band-to-band Auger recombination mechanisms, the non-radiative exciton Auger recombination and recombination in the space charge region (SCR) have to be included. To develop the analytical SC characterization formalism, we proposed a simple expression to model the wavelength-dependent external quantum efficiency of the photocurrent near the absorption edge. Based on this parameterization, the theory developed allows for calculating and optimizing the base thickness-dependent short-circuit current, the open-circuit voltage, and the SC photoconversion efficiency. The accuracy of the approach to optimizing solar cell parameters, particularly thickness and base doping level, is demonstrated by its application to three Si solar cells reported in the literature: one with an efficiency of 26.63%, another with 26.81%, and a third with a record efficiency of 27.3%. The results show that the developed formalism enables further optimization of solar cell thickness and doping levels, leading to potential increases in efficiency.