Charge carrier recombination dynamics in a bi-cationic perovskite solar cell.

The compositional engineering is of great importance to tune the electrical and optical properties of perovskite and improve the photovoltaic performance of perovskite solar cells. The exploration of the corresponding photoelectric conversion processes, especially the carrier recombination dynamics, will contribute to the optimization of the devices. In this work, perovskite with mixed methylammonium (MA) and formamidinium (FA) as organic cations, MA0.4FA0.6PbI3, is fabricated to study the influence of the bi-cation on the charge carrier recombination dynamics. X-ray diffraction analysis indicates the existence of the MAPbI3-FAPbI3 phase segregation in the bi-cationic perovskite crystal. The time-resolved photoluminescence dynamics presents a relatively fast carrier recombination process ascribed to the charge transfer from MAPbI3 to FAPbI3 in the bi-cationic perovskite film. The carrier recombination dynamics investigated by transient photovoltage measurements reveals a biphasic trap-assisted carrier recombination mechanism in the bi-cationic device, which involves carrier recombination in the MAPbI3 phase and FAPbI3 phase, respectively. The ultimate presentation of the carrier recombination process is closely related to the charge transfer between the two perovskite phases.

Multiple-Trapping Model for the Charge Recombination Dynamics in Mesoporous-Structured Perovskite Solar Cells.

The photovoltaic performance of organic-inorganic hybrid perovskite solar cells has reached a bottleneck after rapid development in last few years. Further breakthrough in this field requires deeper understanding of the underlying mechanism of the photoelectric conversion process in the device, especially the dynamics of charge-carrier recombination. Originating from dye-sensitized solar cells (DSSCs), mesoporous-structured perovskite solar cells (MPSCs) have shown many similarities to DSSCs with respect to their photoelectric dynamics. Herein, by applying the multiple-trapping model of the charge-recombination dynamic process for DSSCs in MPSCs, with rational modification, a novel physical model is proposed to describe the dynamics of charge recombination in MPSCs that exhibits good agreement with experimental data. Accordingly, the perovskite- and TiO2 -dominating charge-recombination processes are assigned and their relationships with the trap-state distribution are also discussed. An optimal balance between these two dynamic processes is required to improve the performance of mesoporous-structured perovskite devices.

Power output and carrier dynamics studies of perovskite solar cells under working conditions.

Perovskite solar cells have emerged as promising photovoltaic systems with superb power conversion efficiency. For the practical application of perovskite devices, the greatest concerns are the power output density and the related dynamics under working conditions. In this study, the working conditions of planar and mesoscopic perovskite solar cells are simulated and the power output density evolutions with the working voltage are highlighted. The planar device exhibits higher capability of outputting power than the mesoscopic one. The transient photoelectric conversion dynamics are investigated under the open circuit, short circuit and working conditions. It is found that the power output and dynamic processes are correlated intrinsically, which suggests that the power output is the competitive result of the charge carrier recombination and transport. The present work offers a unique view to elucidating the relationship between the power output and the charge carrier dynamics for perovskite solar cells in a comprehensive manner, which would be beneficial to their future practical applications.

Adverse Effects of Excess Residual PbI2 on Photovoltaic Performance, Charge Separation, and Trap-State Properties in Mesoporous Structured Perovskite Solar Cells.

Organic-inorganic halide perovskite solar cells have rapidly come to prominence in the photovoltaic field. In this context, CH3 NH3 PbI3 , as the most widely adopted active layer, has been attracting great attention. Generally, in a CH3 NH3 PbI3 layer, unreacted PbI2 inevitably coexists with the perovskite crystals, especially following a two-step fabrication process. There appears to be a consensus that an appropriate amount of unreacted PbI2 is beneficial to the overall photovoltaic performance of a device, the only disadvantageous aspect of excess residual PbI2 being viewed as its insulating nature. However, the further development of such perovskite-based devices requires a deeper understanding of the role of residual PbI2 . In this work, PbI2 -enriched and PbI2 -controlled perovskite films, as two extreme cases, have been prepared by modulating the crystallinity of a pre-deposited PbI2 film. The effects of excess residual PbI2 have been elucidated on the basis of spectroscopic and optoelectronic studies. The initial charge separation, the trap-state density, and the trap-state distribution have all been found to be adversely affected in PbI2 -enriched devices, to the detriment of photovoltaic performance. This leads to a biphasic recombination process and accelerates the charge carrier recombination dynamics.

Hexaaqua-zinc(II) bis-[4-(2-hydroxy-benzyl-ideneamino)benzene-sulfonate].

In the title compound, [Zn(H(2)O)(6)](C(13)H(10)NO(4)S)(2), a distorted ZnO(6) octa-hedron results from the coordination by the six water mol-ecules. Only three of the water molecules are crystallographically unique, as the Zn atom lies on an inversion center. The Zn-O bond lengths are in the range 2.054 (4)-2.073 (4) Å. A network of hydrogen bonds helps to establish the crystal packing.