Numerical simulations of hole carrier selective contacts in p-type c-Si solar cells

This work presents a systematic analysis of the transport mechanism and surface passivation of tunneling oxide (SiO2)/p-type poly-silicon (poly-Si(p)) junctions applied to p-type crystalline silicon (c-Si) solar cells by means of TCAD numerical simulations. We report on the impact of the buried doped region (BDR) in the c-Si wafer on the transport and passivation of SiO2/poly-Si(p) junctions. We show that a BDR is not necessary for carrier selective contacts (CSCs) with a tunnel oxide thinner than 1.2 nm and for surface recombination velocity at SiO2/c-Si interface below 1·103 cm/s. Then, we explore alternative semiconductors to poly-Si for tunnel oxide passivating contacts. We find that 3C–SiC(p) is a promising candidate thanks to its valence band offset with respect to silicon, driving the wafer surface into a condition of strong accumulation. We show that excellent SiO2/3C–SiC(p) junctions are obtained for doping density of the 3C–SiC(p) larger than 5·1019 cm−3 and for SiO2 thinner than <1.2 nm. Finally, with the aim of deriving guidelines for material selection, we present an investigation on the influence of the electron affinity and bandgap of the semiconductor layer forming the passivating contact, demonstrating that conversion efficiency is maximized for built-in voltages between 0.4 and 2.6 eV.