IMPROVED EQUIVALENT-CIRCUIT AND ANALYTICAL MODEL FOR AMORPHOUS-SILICON SOLAR-CELLS AND MODULES

An improved equivalent circuit for hydrogenated amorphous silicon (a-S i:H) solar cells and modules is presented. It is based on the classic combination of a diode with an exponential current-voltage characteris tic, of a photocurrent source plus a new term representing additional recombination losses in the i-layer of the device. This model/equivale nt circuit matches the I(V) curves of a-Si:H cells over an illuminatio n range of six orders of magnitude. The model clearly separates effect s related to the technology of the device (series and parallel resista nce) and effects related to the physics of the pin-junction (recombina tion losses). It also allows an effective mu tau product in the i-laye r of the device to be determined, characterizing its state of degradat ion.