Characterization of the SnO2/p and ZnO/p contact resistance and junction properties in a-Si p-i-n solar cells and modules

A new method has been developed to characterize the TCO/p contact in a-Si p-i-n superstrate solar cells and modules. The method is applied to a series of devices fabricated at BP Solar on commercial SnO₂ and ZnO-coated SnO₂ having different p-layer recipes and pre-deposition treatments. Values of the contact resistance (R_c ) of 1±0.5 Ω-cm² were found for a wide range of TCO and p-layer processing including ZnO. Temperature dependence of R_c gave barrier height of 40-55 meV. Analysis of devices with a thin ZnO layer on SnO₂ and with different pre-deposition treatments indicates lower V_oc and FF observed with ZnO is not due to the contact but to changes in the p/i junction recombination. The solar cell performance is very sensitive to the ZnO surface treatment but R_c is not. No evidence was found for a blocking or high resistance ZnO/p contact