Open circuit voltage and loss mechanisms in polycrstalline Cu(InGa)Se{sub}2-heterodiodes from photoluminescence studies

摘要

We have analyzed Cu(InGa)Se{sub}2 heterodiodes and film sequences by room temperature absolute photo-luminescence measurements using the regime of AM1.5 equivalent generation rates. The samples investigated include heterodiodes as well as film sequences composed of absorber layers, window layers and contacts as they occur in the conventional process of cell production. We consider illuminated cells and layers as spectrally selective black bodies and evaluate the splitting of the quasi-Fermi levels via Planck's generalized law. The magnitude of the quasi Fermi level splitting can be used to predict the maximum achievable open circuit voltage in the devices. We see a strong influence of the interfaces at the back contact and the window layers on the luminescence signal. We quantity the effect of the interfaces on the maximum achievable open-circuit voltage. Finally we compare the predicted maximum open-circuit voltage with direct electrical measurements on the same devices.