Modeling of current-voltage characteristics of thin film solar cells

An analytical model is developed to study the current-voltage characteristics of thin film solar cells by incorporating exponential photon absorption, carrier trapping and carrier drift in the absorber layer. An analytical expression for the external voltage dependent photocurrent is derived by solving the continuity equation for both electrons and holes assuming the electric field remains uniform in the absorber layer. The analytical results are verified with the numerical self-consistent solution of the steady-state continuity equations and the Poisson’s equation. The overall load current is calculated considering the actual solar spectrum. It is found that the solar cell efficiency critically depends on the transport properties of the carriers that drift towards the bottom contact. The recombination current dominates over the ideal diode current in CdTe based solar cells. The theoretical model is fitted with the published experimental data on various thin film solar cells and shows a very good agreement.