Limits of Contact Selectivity/Recombination on the Open-Circuit Voltage of a Photovoltaic

We analytically calculate fundamental limits on the open circuit voltage (V-oc) of a solar cell imposed by contact selectivity and contact recombination. To do so, we consider a simple model consisting of only carrier generation in an absorber and charge transfer to its contacts enabling an algebraic solution for the relevant partial currents and the calculation of a contact-determined V-oc. An expression for V-oc is determined assuming the partial currents at the contacts linearly depend on the product of the appropriate equilibrium exchange current density and excess carrier concentration at the contact. Quantitatively defining contact selectivity and contact recombination, we illustrate the roles of the exchange current densities, recombination, and selectivity on V-oc. Additionally, we use complete device physics simulations to show that our simplified model is valid in practically relevant situations. The framework we have developed elucidates the physics underlying more qualitative discussions of selectivity often invoked to describe the impact of contacts on V-oc, thereby enabling better-motivated improvements in contact design.