Annealing effect of polymer bulk heterojunction solar cells based on polyfluorene and fullerene blend

Control of blend morphology at the nanoscale and high charge mobility is essential for polymer photovoltaic devices in terms of their power conversion efficiencies (PCE). In the case of bulk heterojunctions solar cells, both blend morphology and charge mobility are influenced by thermal treatment. In this manuscript, we study the effects of annealing temperature on polymer PV devices with blends of poly[9,9'- dioctyl-fluorene-co-bithiophene] (F8T2) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). The morphological changes of blended films were observed upon thermal annealing temperature near and above glass transition temperature (130 °C). Such microstructural transformations resulted in modified charge transport pathways and therefore greately influenced the device performance. The highest PCE of 2.14% with an open-circuit voltage (VOC) of 0.99 V and a short-circuit current (JSC) of 4.24 mA/cm2 was achieved by device annealing at 70 °C for 20 min. © 2008 Elsevier B.V. All rights reserved.