Dyes which function as molecular optical heaters and optical thermometers can be doped into a wide variety of molecular materials. Here we show how picosecond light pulses can be used to deposit a known amount of heat and to measure the temperature, i.e. to perform accurate optical calorimetry, at heating rates up to dT/dt = 10I2 deg/s. Nonequilibrium mechanical energy transfer processes, including mechanical energy flow into or out of molecules by vibrational cooling or multiphonon up pumping, and the physical and chemical properties of superheated liquids and solids are investigated experimentally by ultrafast temperature jump spectrosoopy and theoretically using molecular dynamics simulations. Specific examples presented here include (1) the generation of 750 O C molecular hot spots lasting a few picoseconds, produced at near-IR dye molecule centers which sequentially absorb tens of photons during a picosecond pulse, (2) the production and measurement of bulk temperature jumps AT > 100 O C in liquids and >500 O C in polymers, (3) the investigation of multiphonon up pumping processes in energetic materials by picosecond Raman spectroscopy, and (4) direct solid-state temperature measurements made during laser photothermal surface ablation of polymers using optical calorimetry.
The recombination after flash photolysis of carbon monoxide (CO) to protoheme (PH) in glycerol: water is studied over ten decades in time (1 ps to 10 ms). The rebinding consists of an initial nonexponential geminate phase followed by a slower exponential bimolecular phase. The entire time course of this reaction between 260 and 300 K can be explained in a unified way using a simple, analytically tractable diffusion model involving just three parameters: the relative diffusion constant, the contact radius, and the intrinsic rate of reaction at contact.
Electron transfer involves changes in molecular geometry that are important for controlling rates. In this work we report the first clear effects of vibrational quantum state on solution phase electron transfer rates. The spontaneous electron transfer rates for the recovery of an ion pair [Co(Cp) 2 + /V(CO) 6 -] are studied with picosecond infrared spectroscopy following optical excitation into its charge transfer band. The rates increase about 2-fold for each additional vibrational quantum in the CO stretching mode. These results allow new tests of electron transfer theory.The understanding of molecular electron transfer processes has made enormous progress in the last 20 years. 1 Electron transfer is very diverse, and such processes are important in molecular electronics devices, solar energy conversion, and biological processes. The experimental electron transfer rate normally is given as a single experimental number for a complex system, at some specific temperature and environment. The availability of a single rate has allowed only indirect tests of electron transfer models by averaging over the vibrational details in a quantum mechanical treatment of rate. Our recent experimental work has demonstrated, for the first time, that solution phase electron transfer rates can be measured with vibrational state resolution. 2 In addition, theoretical models 3 predict significant rate changes for some molecules when excited vibrational levels are populated.The earlier molecule we selected for the study of vibrational effects 2 had some complexities in the observed kinetics that made it difficult to demonstrate both the quantum-resolved electron transfer rates and the correlated vibrational activity in the molecule after the electron transfer. Therefore, we report data for a new molecule that resolves these key experimental points and which we believe can serve as a major test of theoretical electron transfer models in the future. The less informative case of vibrational activity following electron transfer should be observable in many molecules, and such a case was reported for ultrafast electron transfer. 4 The idea that multiple electron transfer rates, rather than a single rate, can be observed in the liquid phase was not previously recognized as possible because it is usually thought that complex molecules redistribute vibrational energy much faster than they transfer electrons. The processes of intramolecular vibrational redistribution (IVR) and vibrational relaxation (VR) are indeed quite fast; however, electron transfer also can be fast, and in certain molecules some vibrational modes can have lifetimes in the hundreds of picoseconds due to their high frequencies and wide separation from other frequencies. One such class of molecules includes the metal carbonyls, as shown by direct lifetime measurements of vibrational lifetimes. 5 The molecule of interest is a molecular ion pair, specifically associated in a low dielectric solvent. The ion pair has sufficient electronic interaction to form a weak charge transf...
Choline chloride as a photosynthesis promoter is important for increasing plant yield, and we have found that it has a similar effect in perovskite solar cells (PSCs). Here, we propose the innovation of using molecular self-assembly methods to produce a choline chloride monolayer on the surface of the SnO 2 ; this monolayer works as a passivation layer that reduces the surface oxygen vacancies and improves the performance of CH 3 NH 3 PbI 3 (MAPbI 3 ) PSCs. The MAPbI 3 PSC based on SnO 2 modified by choline chloride (Chol-SnO 2 ) electron transport layer (ETL) achieves an optimal power conversion efficiency (PCE) of 18.90% under one solar illumination. The PCE is increased by 10−25% compared to the device without modification, and hysteresis is significantly reduced by eliminating the charge accumulation between the interface of the perovskite and ETL. More importantly, the MAPbI 3 PSC based on Chol-SnO 2 ETL exhibits a higher open-circuit voltage (V OC ) of 1.145 V compared to the control device (1.071 V). This work provides a very simple and effective way to improve PSC performance, which has long-term significance for the sustainable development of energy.
Co-modification of an electron transport layer (ETL) with metal oxides and organic molecules can optimize the structure of the ETL and improve the performance of perovskite solar cells (PSCs).
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