| Autor: |
O'Hara KA; Materials Department, University of California Santa Barbara , Santa Barbara, California 93106, United States., Ostrowski DP; National Renewable Energy Laboratory (NREL) , Golden, Colorado 80401, United States., Koldemir U; Department of Chemistry, Colorado School of Mines , Golden, Colorado 80401, United States., Takacs CJ; Materials Department, University of California Santa Barbara , Santa Barbara, California 93106, United States., Shaheen SE, Sellinger A; Department of Chemistry, Colorado School of Mines , Golden, Colorado 80401, United States., Chabinyc ML; Materials Department, University of California Santa Barbara , Santa Barbara, California 93106, United States. |
| Abstrakt: |
Many high efficiency organic photovoltaics use fullerene-based acceptors despite their high production cost, weak optical absorption in the visible range, and limited synthetic variability of electronic and optical properties. To circumvent this deficiency, non-fullerene small-molecule acceptors have been developed that have good synthetic flexibility, allowing for precise tuning of optoelectronic properties, leading to enhanced absorption of the solar spectrum and increased open-circuit voltages (V OC ). We examined the detailed morphology of bulk heterojunctions of poly(3-hexylthiophene) and the small-molecule acceptor HPI-BT to reveal structural changes that lead to improvements in the fill factor of solar cells upon thermal annealing. The kinetics of the phase transformation process of HPI-BT during thermal annealing were investigated through in situ grazing incidence wide-angle X-ray scattering studies, atomic force microscopy, and transmission electron microscopy. The HPI-BT acceptor crystallizes during film formation to form micron-sized domains embedded within the film center and a donor rich capping layer at the cathode interface reducing efficient charge extraction. Thermal annealing changes the surface composition and improves charge extraction. This study reveals the need for complementary methods to investigate the morphology of BHJs. |
