Photogenerated carrier dynamics of Mn2+ doped CsPbBr3 assembled with TiO2 systems: Effect of Mn doping content.

In recent years, all-inorganic perovskite materials have become an ideal choice for new thin film solar cells due to their excellent photophysical properties and have become a research hotspot. Studying the ultrafast dynamics of photo-generated carriers is of great significance for further improving the performance of such devices. In this work, we focus on the transient dynamic process of CsPbBr3/TiO2 composite systems with different Mn2+ doping contents using femtosecond transient absorption spectroscopy technology. We used singular value decomposition and global fitting to analyze the transient absorption spectra and obtained three components, which are classified as hot carrier cooling, charge transfer, and charge recombination processes, respectively. We found that the doping concentration of Mn2+ has an impact on all three processes. We think that the following two factors are responsible: one is the density of defect states and the other is the bandgap width of perovskite. As the concentration of doped Mn2+ increases, the charge transfer time constant shows a trend of initially increasing, followed by a subsequent decrease, reaching a turning point. This indicates that an appropriate amount of Mn2+ doping can effectively improve the photoelectric performance of solar cell systems. We proposed a possible charge transfer mechanism model and further elucidated the microscopic mechanism of the effect of Mn2+ doping on the interface charge transfer process of the CsPbBr3/TiO2 solar cell system.

Effect of Cs+ Doping on the Carrier Dynamics of MAPbI3 Perovskite.

Organic inorganic perovskite materials have received increasing attention in the optoelectronic field because of their unique properties. The ultrafast dynamics of photogenerated carriers determine photoelectric conversion efficiency, thus, it is feasible to influence the dynamics behavior of photogenerated carriers by regulating A-site cations. This paper mainly used transient absorption spectra (TAS) technology to study the photogenerated carriers relaxation processes of organic-inorganic perovskite CsxMA1-xPbI3 materials at different x values. Three sets of time constants were obtained by global fitting at different values of x. The experimental results showed that the crystal structure of perovskite could be affected by adjusting the Cs+ doping amount, thereby regulating the carrier dynamics. The appropriate amount of A-cation doping not only maintained the organic-inorganic perovskite crystal phase, but also prolonged the photogenerated carrier's lifetime. The 10% Cs+ doping CsxMA1-xPbI3 perovskite has potential for solar cell applications. We hope that our research can provide dynamics support for the development of organic-inorganic perovskite in solar cells.

Pressure-Induced Tunable Charge Carrier Dynamics in Mn-Doped CsPbBr3 Perovskite.

All-inorganic perovskite materials (CsPbX3) have attracted increasing attention due to their excellent photoelectric properties and stable physical and chemical properties. The dynamics of charge carriers affect the photoelectric conversion efficiencies of perovskite materials. Regulating carrier dynamics by changing pressure is interesting with respect to revealing the key microphysical processes involved. Here, ultrafast spectroscopy combined with high-pressure diamond anvil cell technology was used to study the generation and transfer of photoinduced carriers of a Mn-doped inorganic perovskite CsPbBr3 material under pressure. Three components were obtained and assigned to thermal carrier relaxation, optical phonon-acoustic phonon scattering and Auger recombination. The time constants of the three components changed under the applied pressures. Our experimental results show that pressure can affect the crystal structure of Mn-doped CsPbBr3 to regulate carrier dynamics. The use of metal doping not only reduces the content of toxic substances but also improves the photoelectric properties of perovskite materials. We hope that our study can provide dynamic experimental support for the exploration of new photoelectric materials.

Dynamical and allosteric regulation of photoprotection in light harvesting complex II.

Major light-harvesting complex of photosystem II (LHCII) plays a dual role in light-harvesting and excited energy dissipation to protect photodamage from excess energy. The regulatory switch is induced by increased acidity, temperature or both. However, the molecular origin of the protein dynamics at the atomic level is still unknown. We carried out temperature-jump time-resolved infrared spectroscopy and molecular dynamics simulations to determine the energy quenching dynamics and conformational changes of LHCII trimers. We found that the spontaneous formation of a pair of local α-helices from the 310-helix E/loop and the C-terminal coil of the neighboring monomer, in response to the increased environmental temperature and/or acidity, induces a scissoring motion of transmembrane helices A and B, shifting the conformational equilibrium to a more open state, with an increased angle between the associated carotenoids. The dynamical allosteric conformation change leads to close contacts between the first excited state of carotenoid lutein 1 and chlorophyll pigments, facilitating the fluorescence quenching. Based on these results, we suggest a unified mechanism by which the LHCII trimer controls the dissipation of excess excited energy in response to increased temperature and acidity, as an intrinsic result of intense sun light in plant photosynthesis.

Morphology and electrical characteristics of p-type ZnO microwires with zigzag rough surfaces induced by Sb doping.

Sb-doped p-type ZnO microwires with zigzag rough surfaces were synthesized by two zone chemical vapor deposition. The zigzag morphology characteristics analyzed by high resolution scanning electron microscopy and transmission electron microscopy show the existence of surface defects caused by Sb doping. The incorporation of Sb into a ZnO lattice induces lattice imperfection, which is the origin of the zigzag rough surface. Photoluminescence and electrical properties of the obtained Sb-doped ZnO microwires were determined. The crossed structure microwire-based p-n homojunction device was fabricated by applying as-synthesized Sb-doped p-type ZnO microwires and undoped n-type ZnO microwires. The doped microwires demonstrate reproducible p-type conduction and enhanced rectifying behavior with increasing Sb doping concentration. The results demonstrated that the optimizable optical and electrical characteristics, controlled by increasing the doping concentration, are reflected in the surface morphology changes which would be helpful for characterizing the doping effects in micro/nanoscale materials.

Zn-Zn porphyrin dimer-sensitized solar cells: toward 3-D light harvesting.

Zn-Zn porphyrin dimers have been incorporated into thin dye-sensitized solar cells (DSSCs) to boost their light harvesting efficiency. The photoexcited dimers show efficient and fast electron injection into TiO(2) indicating that both photoexcited chromophores contribute to current generation. The improved light harvesting ability coupled to enhanced DSSC performance demonstrates the potential of 3-D light harvesting arrays as next generation light harvesters for artificial solar energy conversion systems.

Ultrafast plasmon-induced electron transfer from gold nanodots into TiO2 nanoparticles.

By using femtosecond transient absorption spectroscopy with visible pump and IR probe to observe generation of injected electrons, we could directly observe plasmon-induced electron transfer from 10 nm gold nanodots to TiO2 nanocrystalline film. It was revealed that the reaction time was within 240 fs and the yield was about 40%.

Protein structural deformation induced lifetime shortening of photosynthetic bacteria light-harvesting complex LH2 excited state.

Photosynthetic bacterial light-harvesting antenna complex LH2 was immobilized on the surface of TiO(2) nanoparticles in the colloidal solution. The LH2/TiO(2) assembly was investigated by the time-resolved spectroscopic methods. The excited-state lifetimes for carotenoid-containing and carotenoidless LH2 have been measured, showing a decrease in the excited-state lifetime of B850 when LH2 was immobilized on TiO(2). The possibility that the decrease of the LH2 excited-state lifetime being caused by an interfacial electron transfer reaction between B850 and the TiO(2) nanoparticle was precluded experimentally. We proposed that the observed change in the photophysical properties of LH2 when assembled onto TiO(2) nanoparticles is arising from the interfacial-interaction-induced structural deformation of the LH2 complex deviating from an ellipse of less eccentric to a more eccentric ellipse, and the observed phenomenon can be accounted by an elliptical exciton model. Experiment by using photoinactive SiO(2) nanoparticle in place of TiO(2) and core complex LH1 instead of LH2 provide further evidence to the proposed mechanism.