Impact of CdTe surface composition on doping and device performance in close Space sublimation deposited CdTe solar cells

Cool‐down after close‐space sublimation growth of cadmium telluride films has been shown to lead to the formation of a Cd‐rich surface that can block the subsequent in‐diffusion of cadmium chloride that is used in post‐growth doping of solar cell devices. Pre‐etching of the as‐grown surfaces using a nitric–phosphoric acid etch prior to doping leads to increase in chlorine and oxygen in‐diffusion, and an associated improvement in device efficiency from <3% to 12% in controlled trials. Capacitance‐voltage analysis of such devices revealed an increase in the acceptor concentration from 3.76 × 10 13  cm −3 to 5.6 × 10 14  cm −3 , whereas thermal admittance spectroscopy revealed fewer deep states at energies >0.4 eV for etched devices. Impedance analysis showed the improved cadmium chloride treatment—resulting from the additional etching step—removed the grain boundary component from the equivalent circuit, indicating a grain boundary passivation effect. Copyright © 2011 John Wiley & Sons, Ltd.