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Unveiling the photophysics of thiourea from CASPT2/CASSCF potential energy surfaces and singlet/triplet excited state molecular dynamics simulations
摘要： This work describes the decay mechanism of photoexcited thiourea, both in gas phase and in solution, from the information inferred from the topography of the excited and ground state potential energy surfaces and mixed singlet/triplet quantum classical molecular dynamics simulations. Our gas phase results reveal T1/S0 intersystem crossing as the dominant (49%) intrinsic decay channel to the ground state, which reaches a population of 0.28 at the final time of our simulations (10 ps). Population of the T1, would occur after internal conversion to the S1 from the spectroscopic S2 electronic state, followed by S1->T2 intersystem crossing and T2->T1 internal conversion processes. Minor decay channels occurring exclusively along the singlet manifold, i.e. S2->S0 (33%) and S1->S0 (18%), were also observed to play a role in the relaxation of photoexcited thiourea in the gas phase. The explicit incorporation of water-thiourea interactions in our simulations was found to provoke a very significant delay in the decay to the ground state of the system, with no transitions to the S0 being registered during the first 10 ps of our simulations. Intermolecular vibrational energy redistribution and explicit hydrogen bond interaction established between water molecules and the NH2 group of thiourea were found to structurally or energetically hamper the access to the intersystem crossing or internal conversion funnels with the S0.
关键词： intersystem crossing,internal conversion,CASPT2 calculations,thiourea,molecular dynamics simulations
更新于2025-09-19 17:15:36
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Sequential deposition route to efficient Sb <sub/>2</sub> S <sub/>3</sub> solar cells
摘要： We report a facile two-step sequential deposition method to prepare Sb2S3 thin films, where antimony acetate and thiourea are utilized as antimony and sulfur sources, respectively. The sequential deposition of two precursor materials followed by swift annealing at mild temperature leads to high-quality Sb2S3 films. The detailed reaction mechanism is revealed on the basis of structural and compositional analyses. By optimizing the concentration of thiourea and annealing temperature, uniform and flat Sb2S3 thin films are obtained with either sulfur-deficiency or sulfur richness. Finally, a planar heterojunction solar cell based on the as-prepared Sb2S3 film delivers a high power conversion efficiency of 5.69%, which is a top value for planar heterojunction Sb2S3 solar cells fabricated by a solution approach. This research provides a convenient and low-cost approach for the deposition of Sb2S3 films for efficient solar cell applications.
关键词： antimony acetate,Sb2S3,sequential deposition,thiourea,solar cells
更新于2025-09-11 14:15:04