Kinetic studies of carrier transport and recombination at the n-silicon/methanol interface

The response of the open-circuit photovoltage, V_oc, has been investigated with regard to changes in the minority carrier diffusion length, majority carrier density, short-circuit photocurrent density, and cell temperature of n-Si/CH₃OH junctions. The reaction kinetics are observed to be first order in dopant density, minority carrier diffusion length, and photocurrent density. The activation barrier for carrier recombination, obtained from plots of V_oc vs. temperature, is 1.15 ± 0.05 eV. An optimum dopant density for maximum V_oc is observed, and this is consistent with bulk lifetime measurements on similarly doped Si samples. The reaction kinetics are not sensitive to the concentration of redox species (at constant electrochemical potential), indicating minimal recombination losses due to poor interfacial charge transport rates. V_oc values for optimally doped systems (V_oc = 670 mV for 0.015 Ω-cm n-Si samples at 20 mA/cm² photocurrent densities) represent the highest photovoltages obtained to date for any n-Si-based surface barrier device. Surface recombination velocity measurements at the n-Si/CH₃OH interface have been performed, and correlations between the surface recombination rate and the improvement in current-voltage properties have been investigated.