研究目的
Understanding the mechanism of charge separation at the organic donor/acceptor interface and studying the temporal evolution of the charge-transfer state (CTS) in the PCDTBT/PC71BM blend using out-of-phase Electron Spin Echo (ESE) spectroscopy.
研究成果
The study developed a protocol for determining the CTS lifetime for a certain electron-hole distance in the donor/acceptor OPV blend based on low-temperature out-of-phase ESE traces. The temporal evolution of the CTS population for a certain electron-hole distance was extracted, and an extremely low attenuation factor for the CTS recombination rate β = 0.08 ??1 was derived, likely due to strong delocalization of the hole along the PCDTBT chain.
研究不足
The study assumes that charge diffusion is slow on the microsecond scale, spin relaxation times for thermalized trapped charges and charges forming CTSs coincide, spin coupling within CTSs is weak, exchange interaction between the electron and the hole forming the CTS is much smaller than dipolar interaction, and the initial spin state of CTSs is pure singlet. These assumptions may not hold for all organic photovoltaic blends.
1：Experimental Design and Method Selection:
The study utilized out-of-phase Electron Spin Echo (ESE) spectroscopy to investigate the CTS in the PCDTBT/PC71BM blend. The protocol for determining the CTS geminate recombination rate for certain electron-hole distances was developed.
2：Sample Selection and Data Sources:
The PCDTBT/PC71BM blend was prepared with a weight ratio of 1:1 from chlorobenzene solution, and the composite was formed on the inner wall of the EPR sample tube and on quartz plates.
3：List of Experimental Equipment and Materials:
An X-band ELEXSYS ESP-580E EPR spectrometer equipped with an ER 4118 X-MD-5 dielectric cavity inside an Oxford Instruments CF 935 cryostat was used. The sample was illuminated by laser flashes from the TECH laser.
4：Experimental Procedures and Operational Workflow:
The sample was illuminated by laser flashes, and ESE measurements were carried out at different temperatures. The out-of-phase ESE traces were measured for different delays after the laser flash.
5：Data Analysis Methods:
The out-of-phase ESE traces were numerically modeled to determine the electron-hole distance distribution function and its evolution over time.
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