The key process in organic solar cell operation is charge separation under light illumination. Due to the low dielectric constant of organic materials, the Coulomb attraction energy within the interfacial charge-transfer state (CTS) is larger than the thermal energy. Understanding the mechanism of charge separation at the organic donor/acceptor interface still remains a challenge and requires knowledge of the CTS temporal evolution. To address this problem, the CTS in the benchmark photovoltaic blend PCDTBT/PC71BM was studied by the out-of-phase Electron Spin Echo (ESE). The protocol for determining the CTS geminate recombination rate for certain electron-hole distances was developed. Simulating the out-of-phase ESE trace for the CTS in the PCDTBT/PC71BM blend allows precise determination of the electron-hole distance distribution function and its evolution with the increase in the delay after the laser flash. Distances of charge separation up to 6 nm were detected upon thermalization at a temperature of 20 K. Assuming the exponential decay of the recombination rate, the attenuation factor β = 0.08 Å−1 is estimated for the PCDTBT/PC71BM blend. Such a low attenuation factor is probably caused by a high degree of hole delocalization along the PCDTBT chain.
The reaction of trans-[Ru(NO)Py 2 Cl 2 (OH)] with concentrated o-phosphoric acid, after washing the mixture with diethyl ether, gave trans-[Ru(NO)Py 2 Cl 2 (H 2 O)]H 2 PO 4 •2H 3 PO 4 •H 2 O (I) in nearly quantitative yield. The structure of this compound was determined by X-ray diffraction analysis: space group P-1. Washing of I with ethanol afforded the dihydrophosphate salt trans-[Ru(NO)Py 2 Cl 2 (H 2 O)]H 2 PO 4 •H 2 O (II) (yield 97%). The thermal decomposition of I and II in a helium atmosphere resulted in the formation of ruthenium phosphide RuP as a predominant component along with Ru 2 P or RuP 2. Preliminary photoisomerization experiments for trans-[Ru(NO)Py 2 Cl 2 (OH)] and trans-[Ru(NO)Py 2 Cl 2 (H 2 O)]H 2 PO 4 •H 2 O suggested the presence of metastable states. DSC experiments have been carried out for both compounds. The measured kinetic parameters for the metastable decay for trans-[Ru(NO)Py 2 Cl 2 (H 2 O)]H 2 PO 4 •H 2 O were E a = 90.7± 2.4 kJ/mol, log 10 (k 0 /sec −1) = 18.9±0.6, and T d = 217 K.
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