CuInSe2/CdS simulation and modeling

A simulator that can deduce the carrier density and diffusion length from experimental QE (quantum efficiency) curves at different applied voltages has been developed, and applied to CIS solar cells produced by a novel sputtering approach. An analytic expression for the dark diode current of an insulating graded bandgap solar cell has been obtained for the case of the gap increasing linearly away from the junction. The results indicate a diode factor ranging from ~1.6 at low voltages to 2 at higher voltages. An increase in open-circuit voltage is expected to be roughly half of the increase in the energy gap, subject, however, to a maximum value set by the smaller of the built-in voltages in the conduction or valence bands