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 × 1013 cm−3 to 5.6 × 1014 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.