The effect of deposition method and thickness dependence on the growth of P3HT for organic photovoltaic devices

This study presents a comparison between spin-coating, dip-coating, and drop-coating that entails investigating the effect of the thickness on P3HT thin film properties. The grown P3HT thin films were characterized using a range of analytical techniques to evaluate their structural, morphological and optical properties. The XRD of P3HT thin films revealed strong thickness dependence where 30 nm thin film had low diffraction intensity and 148 nm thin film revealed the highest intensity. The nanoball morphology which varies in terms of distribution and clustering based on deposition method was attained. From the FTIR measurements, we observed no noticeable change in vibrational frequencies regardless of the deposition method and the thin film thickness. The abnormalities in absorption measurements suggest thickness dependence due to various deposition methods that resulted in oxygen defect-related states that modified the energy band gap. From PL analysis we observed an increase in the emission intensity following the increase in thin film thickness which denotes the change in P3HT conformation as the number of defects increases. Thus, the drop-coating method produced a thicker thin film that revealed outstanding structural and optical properties that are vital for organic photovoltaic (OPV) device functioning. Even though the drop-coating method produced thin films with promising results for OPV devices, it lacks in terms of reproducibility such as controlling thin film thickness which causes extrinsic degradation effects. Thus, the spin-coating method is viable as one can control spin speed to attain the desired thickness for optimum performance of P3HT in OPV devices.