Copper(I) thiocyanate (CuSCN) is a stable, wide band gap p-type semiconductor being developed for applications in a broad range of optoelectronic devices. In this thesis, aerosol-assisted chemical vapour deposition (AACVD) is explored as a novel technique for the scalable deposition of CuSCN for use as a hole transport material in perovskite solar cells (PSCs).
Detailed studies were conducted to determine the optimum solvent and deposition conditions required to deposit uniform, reproducible thin films of CuSCN. The solvent of choice was determined to be diethyl sulphide containing 35 mg/ml of CuSCN, that was aerosolised into the AACVD reactor using a N2 carrier gas with a flow rate of 0.5 dm3/min and deposited onto a heated substrate at 60 °C. Growth rates >100 nm/min resulted in the deposition of continuous, pinhole free films over an area of 28 cm2. By analysing the time dependent growth properties, film growth was determined to follow a Volmer-Weber type growth. Comprehensive film characterisation was carried out to determine morphology, composition, optical, structural and charge transport properties.
The unique ability of AACVD to deposit ultra-thick CuSCN films (~1.5-4 μm) were exploited to determine the out-of-plane mobility for the first time via the time-of-flight (ToF) technique. The thickness independent hole mobility was identified to be ~10-3 cm2/Vs with a weak electric field dependence of 0.005 cm/V1/2.
The performance of AACVD CuSCN in various PSC architectures were evaluated and compared with the current literature as well as spin coated CuSCN analogues prepared in-house. Champion PSCs were obtained using TiO2 electron transport layers and methylammonium lead iodide as the photoactive perovskite. Comparable power conversion efficiencies were obtained for the AACVD and spin coated CuSCN devices, despite the AACVD layers being more than an order of magnitude thicker confirming the excellent charge transport properties of AACVD CuSCN.