Atomic Layer Deposition of CuxS for Solar Energy Conversion

Thin films of photoactive Cu 1.8 S have been deposited by atomic layer deposition (ALD) using Cu(thd) 2 and H 2 S as the precursors. This is a first step in the construction of nanoporous heterojunctions of TiO 2 /Cu 1.8 S. The ALD process can be divided into two temperature regimes: below 175 °C, adsorption of the complete Cu(thd) 2 molecule occurs, followed by an exchange reaction with H 2 S yielding CuS; above 175 °C, Cu(thd) 2 reduces upon adsorption and slowly decomposes yielding Cu 1.8 S. The slow decomposition of Cu(thd) 2 ensures that smooth and homogeneous films can be obtained up to 280 °C. Flat film solar cell devices of TiO 2 /Cu 1.8 S have an open‐circuit voltage of about 200 mV and a short‐circuit current of 30 μA cm –2 at 2.8 kW m –2 .