Effects of Thin Film Morphology of Polymer Hole Transfer Material on Photovoltaic Performance of Perovskite Solar Cells

Abstract

In the present study, the effects of chain length variation of Poly(3-hexyl) thiophene polymer, which is one of the appropriate alternatives of Spiro-O-MeTAD used as a hole transfer layer (HTL) in perovskite-based solar cells (PSC), on thin-film morphology and device performance were investigated. Furthermore, nanowires of long (UZ) and short-chain (KZ) P3HT were obtained in the solution phase and then comparative photovoltaic performance analyses were carried out by fabricating PSC devices. As a result, it was determined that the morphological changes resulting from the polymer chain length directly affect the charge transfer between the active layer and HTL. KZ-P3HT presented better performance than both standard P3HT (5.99) and UZ-P3HT (2.68) polymers with a power conversion efficiency (PCE) of 7.74%. It was demonstrated that the main reason for this is that the fringed structure, detected by AFM images, increases the contact ratio at the perovskite/HTM interface. In addition, thanks to the morphological improvements in nano-wire studies, it was observed that the photovoltaic performance of the PSC device containing UZ-P3HT increased by 5.51%. Contrary to UZ-P3HT, it was determined that after the conversion of KZ-P3HT to the nanowire, the fringed structure on the surface disappeared and therefore the efficiency decreased to 5.81%.