Effect of In Situ Annealing on Phase Segregation And Optoelectronic Properties of Ultrasonic-Spray Deposited Polymer Blend Films

Here, we report a systematic study on the various effects of in situ annealing on nanoscale phase segregation and optoelectronic properties of ultrasonic spray deposited Poly (3-hexylthiophene) (P3HT): [6,6]-Phenyl-C71-butyric acid methyl ester (PC71BM) blend film and compared their photovoltaic properties with state-of-art spin-coated devices. Detailed investigations have been carried out to understand the structure-property relationship between the polymer crystallization process, film formation, and charge transport for such deposition technique. It has been found that ultrasonic spray coating at moderate substrate temperature, well below the solvent boiling point, results in the best quality films with comparable properties to spin-coated samples. Films deposited at 80 °C showed uniform crystallite size of approximately 8.6 nm, photoluminescence quenching around ~98%, and improved charge transport properties with electron and hole mobility of 7.8 × 10 ^-3 cm ² V ^-1 s ^-1 and 9.41 × 10 ^-6 cm ² V ^-1 s ^-1 , respectively. The photovoltaic devices obtained for such condition exhibited a power conversion efficiency of 2.45%. The similarities in film characteristics and device performances between spin and ultrasonic spray deposited samples indicate its practical feasibility as a scalable technique for large area applications.