Poly-Si passivating contacts prepared via phosphorus spin-on-doping: A comparison between different silicon deposition methods

Polycrystalline silicon-based (poly-Si) passivating contacts are a promising technology for the next generation of high-efficiency crystalline silicon solar cells. Ex-situ doping via spin-on-dopant solutions is a potential method to fabricate patterned poly-Si contacts, like those used in interdigitated back contact architectures. This study compares the performance of phosphorous doped poly-Si passivating contacts fabricated from different industry-compatible intrinsic silicon films and a spin-on-dopant process. We explore the influence of the grain size on the electrical quality of the poly-Si films and find a correlation between larger grain size and lower contact recombination and resistivity. The best results are achieved with low-pressure chemical vapor deposited poly-Si films, reaching an implied open circuit voltage iVoc of 730 mV, followed by plasma-enhanced chemical vapor deposited films with an iVoc of 700 mV. Both films also produced low contact resistivities of <50 mΩ-cm2. For the case of physical vapor deposition (sputtered) poly-Si films, which are found to have the smallest crystalline features, a low iVoc of 625 mV was measured, attributed to a low active dopant concentration within the poly-Si film. This study informs researchers looking to use spin-on-dopants in terms of the poly-Si layer deposition method and the optimal temperature profiles for the process.