Optimization of Nickel Oxide/FTO based HTL Thin Films for Solar Cell Applications

Abstract

In this research study, compact Nickel oxide (NiO) thin films were studied for their potential application as hole selective layers (HSL) in perovskite solar cells (PSCs). The films were deposited on top of Fluorine doped Tin Oxide (FTO) coated conductive glass substrates. Different thin film deposition techniques were used including spin coating, electrodeposition, and dip coating. However, dip-coating was preferred during most of this research work because of good surface coverage and film uniformity as compared to electrodeposition and spin coating. The dip-coating is a scalable solution-processable thin film deposition technique thus, it is a simple and economical route towards shifting from lab-scale devices to large-sized commercial PSCs. In this research study, the dip coating was performed under ambient conditions using 85 mm/min withdrawal speed. 0.5M solution of NiAc2.4H2O dissolved in ethanol was used as a precursor solution. After drying and calcination, the films were characterized using Raman, XRD, EDS and UV-Vis spectroscopy to confirm the successful synthesis of NiO films. The optical profilometry was used to investigate the variation in film thickness as a function of dipping time. Cyclic Voltammetry (CV) revealed that the reaction activity of the NiO thin film increases with time and uniformity. The influence of plasma treatment prior to the dip-coating procedure was studied against the optical and electrical properties of the NiO thin films. One of the important observations during this research work indicated that plasma treatment tends to enhance transmittance of NiO thin films due to increase in their band gap and increased surface coverage.