Optimized Phase Separation in Heterojunction Solar Cells by Controlling Drying Condition

Desired morphology of the blend of solution processed organic photovoltaic devices can be controlled by varying coating process conditions and by subsequent heat treatments. In this work, we observed the effect of drying time & temperature on active layer nano-morphology which leads to change in device performance. At different drying conditions, fullerene molecules agglomerate and form crystallites of varying size. It is observed that the devices with fullerene crystallites of size 10–30 μm show optimum device performance consistently. Thus a certain degree of fullerene molecule diffusion and subsequent agglomeration is desired (quantified by the resultant size of fullerene crystallites). The same can be controlled through drying time and temperature. The results have been supported through characterization such as optical microscope image, absorption spectra, I-V characteristic and AFM images.