Abstract
In this paper, we investigated the recombination dynamics of photogenerated charge carriers in a poly(3-hexylthiophene) (P3HT):[6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) blend system with donor-acceptor ratio of 1:1 before and after solvent annealing treatment. The technique of transient photocurrent and photovoltage measurements were used, and charge carriers were photogenerated by a 7 ns laser pulse at room temperature (298 K). In transient photocurrent measurement, we observed some differences in the saturation extracted charge in P3HT:PCBM solar cells with different power efficiencies. In addition, the bimolecular recombination coefficient β is found to be 3.5×10−13 cm3 s−1 for annealed devices, while 9.5×10−12 cm3 s−1 for as-cast devices. In the transient photovoltage measurement, we found that the photovoltage decay can be fitted by power-law equation at long time scale. The exponent parameter α is 2.6 for annealed devices, which can be described as trap-free bimolecular recombination; α is 1.76 for as-cast device due to the trap-limited bimolecular recombination. These experimental results indicate that the nanomorphology of active layer indeed have influence on charge carriers dynamics in P3HT:PCBM blend systems.
Highlights
In this paper, we investigated the recombination dynamics of photogenerated charge carriers in a poly(3-hexylthiophene) (P3HT):[6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) blend system with donor-acceptor ratio of 1:1 before and after solvent annealing treatment
We investigated the relationship between the nanostructure and charge carrier recombination dynamics, and try to understand how the nanostructure limits the performance of P3HT:PCBM solar cells using transient photocurrent and transient photovoltage measurements
We investigated the nanostructure of P3HT:PCBM using UV-vis absorption spectroscopy, atomic force microscopy (AFM) and X-ray diffraction, while transient photocurrent and photovoltage measurements were used to probe the dynamics of charge carrier in the solar cells
Summary
P3HT and PCBM were mixed together at 1:1 weight ratio into the odichlorobenzene (o-DCB), the concentration of the blend solution was 20 mg mL 1 and stirred overnight. After baking at 120°C for 20 min in an oven, the poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) layer (~40 nm) was spin-coated onto a precleaned ITO coated glass, and subsequently annealed at 100°C for 10 min. The P3HT:PCBM photoactive layer was spin-coated from the blend odichlorobenzene solution at a speed of 1000 r min 1 for 30 s. For the as-cast films, they just were left in the argon glovebox (O2 and H2O concentration both below 10 7). Annealing treatment was performed by leaving the P3HT:PCBM blend films on a petri dish under o-DCB vapour atmosphere in the argon glovebox. The structure of the solar cell is ITO/PEDOT:PSS /P3HT:PCBM/Al
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