Boosting Infrared Light Harvesting by Molecular Functionalization of Metal Oxide/Polymer Interfaces in Efficient Hybrid Solar Cells

摘要

Hybrid solar cells based on light absorbing semiconducting polymers infiltrated in nanocrystalline TiO_2 electrodes, have emerged as an attractive concept, combining benefits of both low material and processing costs with well controlled nano-scale morphology. However, after over ten years of research effort, power conversion efficiencies remain around 0.5%. Here, a spectroscopic and device based investigation is presented, which leads to a new optimization route where by functionalization of the TiO_2 surface with a molecular electron acceptor promotes photoinduced electron transfer from a low-band gap polymer(poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b0]dithiophene)-alt-4,7-(2,l,3-benzothiadia-zole)] (PCPDTBT) to the metal oxide. This boosts the infrared response and the power conversion efficiency to over 1%. As a further step, by "co-functionalizing" the TiO_2 surface with the electron acceptor and an organic dye-sensitizer, panchromatic spectral photoresponse is achieved in the visible to near-IR region. This novel architecture at the heterojunction opens new material design possibilities and represents an exciting route forward for hybrid photovoltaics.