Abstract
Nano-size thin films comprising poly (3-hexylthiophene) (P3HT) and a fullerene derivative [6, 6] phenyl-C61-butyric acid methyl ester (PCBM) incorporating squarylium dye III (SQ3) are reported. The materials prepared were evaluated for their optical, electrical and photo-conversion efficiency. Active layer materials comprising a blend of P3HT:SQ3:PCBM were deposited by spin-coating to produce thin films measuring 100 nm and subsequently annealed at 140°C for 10 min. The films were characterized by UV-Vis-NIR spectroscopy for their optical properties, atomic force microscopy for surface morphology and film thickness, and electrical properties. Optical measurements for blends incorporating different amounts of dye showed increased photo-absorbance with increasing dye concentration. The combined contribution of SQ3 and thermal annealing resulted in increased power conversion efficiency (η) of pristine P3HT:PCBM solar cells from 1.9 to 3.9 %. The dye in the active layer improved photo-absorption by enhanced light harvesting while thermal treatment improved the nanoscale morphology leading to better metal-film interface contact and broadening of the absorption wavelength range. Key words: Polymer solar cell (PSC), squarylium dye III (SQ3), bulk hetero-junction (BHJ), power conversion efficiency (PCE), poly (3-hexylthiophene (P3HT), [6, 6]-phenyl C60 butyric acid methyl ester (PCBM).
Highlights
Squaraine dyes have been reported as promising small molecules that can be incorporated into polymer solar cells to improve light harvesting capacity owing to their intense absorption in the long wavelength range (Chen et al, 2014)
The light harvesting capacity was increased by broadening the absorption band to near infra red (NIR)
A similar effect was observed as a result of thermal treatment of the ternary system at 140°C.The combined contribution of
Summary
Squaraine dyes have been reported as promising small molecules that can be incorporated into polymer solar cells to improve light harvesting capacity owing to their intense absorption in the long wavelength range (Chen et al, 2014). 5.5% have been obtained in ternary P3HT:PCBM systems incorporating a squaraine dye following thermal annealing (Rao et al, 2014). They observed enhanced absorption in the range 650 to 780 nm relative to. Huang et al (2013) demonstrated experimentally that in addition to extending absorption in the solar spectrum, small molecules, such squaraine dyes (SQ), improved excit on harvesting via Förster resonance energy transfer (FRET). The combined effect of dye inclusion and thermal annealing was to increase power conversion efficiency from 1.9 to 3.9%
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