Influence of fullerene derivative replacement with TiO2 nanoparticles in organic bulk heterojunction solar cells

In an effort to develop hybrid organic solar cells with improved power conversion efficiency (PCE), devices based on poly (3-hexylthiophene) (P3HT):phenyl C61-butyric acid methyl ester (PCBM) active layer and poly (3,4-ethylenedioxythiophene) (PEDOT):poly (styrenesulfonate) (PSS) buffer layers were prepared. A systematic replacement of PCBM was achieved by introducing nanostructured TiO2 (∼15 nm particle size), dissolved separately in chlorobenzene (CB) and 1,2 –dichlorobenzene (DCB), to the (P3HT:PCBM) active layer while keeping a fixed amount for P3HT. To understand the effect of fullerene replacement with the inorganic metal oxide nanoparticles on different properties of resulting devices, a variety of techniques such as Current–Voltage (J–V) characteristics, Field Emission Scanning Electron Microscopy (FESEM), Atomic Force Microscopy (AFM), Ultravoilet-Visible (UV–Vis) Spectrophotometry and External Quantum Efficiency (EQE) were employed. The addition of TiO2 nanoparticles in the active layer improved the power conversion efficiency (PCE) of P3HT:PCBM devices. The addition of TiO2 nanoparticles using CB as solvent enhanced the absorption in visible region and also introduced a red shift in the absorption spectra. A significant increase in EQE was observed for devices with TiO2 nanoparticles in the active layer. Mixing TiO2 also increased the surface roughness of the active layer where TiO2 nanoparticles were found to agglomerate as their concentration increased relative to fullerene derivative. A complete agglomeration of TiO2 was observed in the absence of PCBM.