Efficient polymer solar cells via an all-spray-coated deposition

In this study, we report high performance organic solar cells with spray coated hole-injection and active layers. We were able to achieve high film quality, deduced from surface profilometry, atomic force microscopy and absorption measurements. With an automated ultrasonic spray coater we successfully deposit smooth and uniform PEDOT:PSS in optimum thicknesses of 40 nm and a mixture of P3HT and PCBM in thicknesses in the range 200-250 nm. We controlled the thickness variation to values comparable to spin coated layers by the development of two solvent systems for both the layers, taking advantage of surface tension gradients to create Marangoni flows that enhance the coverage of the substrate and reduce the roughness of the film. Notably, we achieved fill factors above 70% and attributed the improvement to an enhanced P3HT crystallization, which upon optimized post-drying thermal annealing results in a favorable morphology. The optimized devices achieve power conversion efficiency of 3.5%, with fill factor, short circuit current and open circuit voltage of 72%, 8.5 mA/cm2 and 586 mV, respectively.