Numerical simulations were used to assess the relevance of the parameters involved in producing GaAs solar cells (SCs). Optical characteristics of SCs were calculated via OpenFilters software, while device performances were calculated via SCAPS software. Junction thickness, doping level, surface-field layer composition and anti-reflective coating thickness were found to be extremely important parameters, meaning that a small variation of their values may lead to a substantial efficiency reduction. These results indicate that researchers must be very careful when comparing different new-concepts SCs, because small lapses or fluctuations in production processes may enshroud the new-concept related changes.