Abstract:
efficiencies (PCEs) of polymer solar cells with active layers that consist of a mixture of poly(3-hexylthiophene-2,5-diyl) and fullerene derivative
(6,6)-phenyl-C61-butyric acid methyl ester. The PCEs of the solar cells increased from ∼2.3% (for the unannealed devices) to ∼3.7%
for devices annealed at ∼150 ○C. A further increase in thermal annealing temperatures (beyond 150 ○C) resulted in lower PCEs. Further
improvements in the PCEs (from ∼3.7% to ∼5.4%) were observed with pressure application between 0 and 8 MPa. However, a decrease in
PCEs was observed for pressure application beyond 8 MPa. The improved performance associated with thermal annealing is attributed to
changes in the active layer microstructure and texture, which also enhance the optical absorption, mobility, and lifetime of the optically
excited charge carriers. The beneficial effects of applied pressure are attributed to the decreased interfacial surface contacts that are associated
with pressure application. The implications of the results are then discussed for the design and fabrication of organic solar cells with improved
PCEs.
