Nanoscale morphology and performance of molecular-weight-dependent poly(3-hexylthiophene)/TiO₂ nanorod hybrid solar cells

We have investigated the effect of polymer molecular weight on the morphology and performance of poly(3-hexylthiophene)/TiO₂ nanorod hybrid photovoltaic devices by using scanning near field optical microscopy (SNOM), atomic force microscopy (AFM) and confocal Raman microscopy. From the topography and absorption mapping images, it is found that the rod-like structure of the low molecular weight polymer hybrid film consists of a large amount of grain boundaries and has a less continuous absorption mapping image. In contrast, the larger domain structure of the high molecular weight polymer hybrid film exhibits a continuous absorption mapping image, as a result of enhanced polymer stacking and electronic delocalization. The nanoscale morphology of the hybrid samples with different molecular weights also reveals the nature of photovoltaic performance and carrier transport behavior investigated by the time-of-flight technique.