Effect of Annealing on the Photoelectrochemical Behavior of CuInS2 Nanocrystal Films

Abstract

Photovoltaics based on inorganic thin film absorber layers such as CuInS2 (CIS) are showing promise in overcoming the increasing energy demand. There are, however, challenges that CIS presents before it can be considered cost effective. A typical synthesis employs a high temperature (∼500°C) annealing step with a H2S atmosphere, which can significantly raise the cost of the photovoltaic devices. In this work we report a relatively low temperature, H2S free annealing step (250°C) that produced a photocurrent enhancement in the CIS nanocrystal film based on the comparison of respective photoelectrochemical measurements. Investigations into the effects of annealing on the morphology, composition, crystallinity and temperature of degradation of the film were carried out. A thin CdS buffer layer can provide photocurrent enhancement of the CIS layer, but it is typically added after annealing because temperatures above 300°C will degrade optical properties. The low annealing temperature allowed for CIS and the CdS buffer layer to be annealed together, which produced a further photocurrent density enhancement. The combination of a low temperature annealing along with a large photocurrent enhancement of the CIS/CdS bi-layer could help to improve efficiency in the full device fabrication while still keeping costs low.