Atomic layer deposition of CuxS for solar energy conversion

Thin films of photoactive Cu1.8S have been deposited by atomic layer deposition (ALD) using Cu(thd)(2) and H2S as the precursors. This is a first step in the construction of nanoporous heterojunctions of TiO2/Cu1.8S. The ALD process can be divided into two temperature regimes: below 175degreesC, adsorption of the complete Cu(thd)(2) molecule occurs, followed by an exchange reaction with H2S yielding CuS; above 175 degreesC, Cu(thd)(2) reduces upon adsorption and slowly decomposes yielding Cu1.8S. The slow decomposition of Cu(thd)(2) ensures that smooth and homogeneous films can be obtained up to 280degreesC. Flat film solar cell devices of TiO2/Cu1.8S have an open-circuit voltage of about 200 mV and a short-circuit current of 30 muA cm(-2) at 2.8 kW m(-2).