Experimental demonstration of the effect of field damping layers in quantum-dot intermediate band solar cells

Abstract

Intermediate band solar cells must demonstrate the principle of voltage preservation in order to achieve high conversion efficiencies. Tunnel escape of carriers has proved deleterious for this purpose in quantum dot intermediate band solar cells. In previous works, thick spacers between quantum dot layers were demonstrated as a means of reducing tunnel escape, but this approach is unrealistic if a large number of quantum dot layers have to be grown. In this work we report experimental proof that the use of field damping layers is equally effective at reducing tunnel carrier escape, by reducing the potential drop in the QD-stack and the associated electric field. Moreover, we demonstrate that the fact that tunnel carrier escape takes place under short-circuit conditions does not imply that voltage preservation cannot be achieved. We describe a theory that relates the evolution of the tunnel escape to bias voltage and the preservation of the voltage in an IBSC. Temperature and voltage-dependent quantum efficiency measurements, temperature dependent open-circuit voltage measurements and calculations of the internal electric field in IBSCs serve as the basis of the proposed theory.