Morphological control of conjugated polymers by additive annealing for solar cell applications

• We investigate photovoltaic performance of a conjugated polymer (CP).
• Degree of polymer aggregation is tuned and device performance is correlated with the aggregation of CP.
• The change of surface morphology induced by the aggregation of CP is reviewed.
• The correlation between film morphology and the degree of recombination in organic photovoltaic device was investigated.

A novel conjugated polymer, PVBT, having a D-A type alternating configuration is synthesized for organic photovoltaic application. It exhibits a bimodal-shaped absorption because of intramolecular charge transfer. Comparison of absorption intensity both in the long and the short wavelength region indicates decent chain planarity of PVBT. Organic photovoltaic devices made of PVBT exhibit better performance compared to identical devices from PVTT having a similar chemical structure due to a deeper HOMO energy level and a lower band-gap of PVBT. Additive assisted annealing further improves the device performance, and film morphology analysis reveals the importance of nano-dimensional phase separation to suppress inner-domain recombination.