A simple synthesis of transparent and highly conducting p-type Cu x Al 1- x S y nanocomposite thin films as the hole transporting layer for organic solar cells.

Inorganic p-type films with high mobility are very important for opto-electronic applications. It is very difficult to synthesize p-type films with a wider, tunable band gap energy and suitable band energy levels. In this research, p-type copper aluminum sulfide (Cu x Al 1- x S y ) films with tunable optical band gap, carrier density, hole mobility and conductivity were first synthesized using a simple, low cost and low temperature chemical bath deposition method. These in situ fabricated Cu x Al 1- x S y films were deposited at 60 °C using an aqueous solution of copper(ii) chloride dihydrate (CuCl 2 ·2H 2 O), aluminium nitrate nonohydrate [Al(NO 3 ) 3 ·9H 2 O], thiourea [(NH 2 ) 2 CS], and ammonium hydroxide, with citric acid as the complexing agent. Upon varying the ratio of the precursor, the band gap of the Cu x Al 1- x S y films can be tuned from 2.63 eV to 4.01 eV. The highest hole mobility obtained was 1.52 cm 2 V -1 s -1 and the best conductivity obtained was 546 S cm -1 . The Cu x Al 1- x S y films were used as a hole transporting layer (HTL) in organic solar cells (OSCs), and a good performance of the OSCs was demonstrated using the Cu x Al 1- x S y films as the HTL. These results demonstrate the remarkable potential of Cu x Al 1- x S y as hole transport material for opto-electronic devices.