We report a large area tandem LSC that is based exclusively on carbon dots and exhibits ηint of 23.6% and ηext of 2.3%.
Solar cells, light emitting diodes, and X-ray detectors based on perovskite materials often incorporate gold electrodes, either in direct or indirect contact with the perovskite compound. Chemical interactions between active layers and contacts deteriorate the operation and induce degradation, being the identification of the chemical nature of such interfacial structures an open question. Chemical reactivity of gold in contact with the perovskite semiconductor leads to reversible formation of oxidized gold halide species and explains the generation of halide vacancies in the vicinity of the interface.Electrical biasing induces contact reaction and produces modifications of the current level by favoring the ability of perovskite/Au interfaces to inject electronic carriers. The current injection increment does not depend on the halogen source used, either extrinsically by iodine vapor sublimation of Au electrodes, or intrinsically by bias-driven migration of bromide ions. In addition, the formation of a dipole-like structure at the reacted electrode that lowers the potential barrier for electronic carriers is confirmed. These findings highlight adequate selection of the external contacts and suggest the need for a deeper understanding of contact reactivity as it dominates the operation characteristics, rather than being governed by the bulk transport properties of the charge carriers, either electronic or ionic.conversion in the near future. In addition to photovoltaic applications, perovskitebased materials are being explored as sensitive layers for high-energy radiation detectors and imaging devices for medical diagnostics. [2] These detection technologies rely upon the ability of perovskite compounds of absorbing high-energy photons and convert their energy into electronic carriers that are finally collected at the outer contacts. For soft X-ray photons (<10 keV), absorbing layer thickness of tens of micrometers suffices to stop the radiation. But hard X-ray radiation (10-50 keV) possesses much longer penetration length (≈100 µm) in compounds as methylammonium lead iodide or bromide (MAPbI 3 and MAPbBr 3 ). [3] Hence, relatively thick layers (0.1-1 mm) need to be employed to achieve sufficient electrical signal. Despite the large electronic carrier mobility and mobility-lifetime product, [4,5] such thick absorbing layers should be externally biased in order to increase the detector responsivity. Electrical fields as high as ≈0.1-1 V µm −1 are commonly needed for poly-crystalline perovskite deposits incorporated into X-ray detectors. [3,5] Large field strength requirements are in some amount lowered when devising single-crystal approaches for X-ray detection using perovskite materials. [4,6] In any case, it is widely recognized that the application of an external bias promotes the displacement and interfacial built-up of intrinsic mobile ions. [7,8] Ion accumulation finally shields the electrical field within the absorbing layer bulk, reducing as a consequence the detector sensitivity. The applicability of perovs...
Temperature-modulated space-charge-limited-current spectroscopy (TMSCLC) is applied to quantitatively evaluate the density of trap states in the band-gap with high energy resolution of semiconducting hybrid lead halide perovskite single crystals. Interestingly multicomponent deep trap states were observed in the pure perovskite crystals, which assumingly caused by the formation of nanodomains due to the presence of the mobile species in the perovskites.
The origin of a negative capacitance observed in perovskite solar cells at intermediate and low frequencies remains unclear. Low trap density macroscopic single crystal MAPbBr3 perovskites, prepared by means of an inverse temperature crystallization technique, with symmetric Au contacts is used to avoid the influence of defects and provide the information ongoing staunchly in the perovskite material. It is shown that the inductive behavior is dominant in the frequency range where capacitance possesses negative values. Accordingly, a model for the calculation of inductive elements and the description of their origin is presented. It is shown that, at high bias, there are two bias‐dependent inductive elements, which corresponds to two different components of vacancy‐assisted ionic diffusion in perovskite crystals, originating from Br– and MA+ ions.
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