Interface inductive currents and carrier injection in hybrid perovskite single crystals

nterfaces between the absorbing perovskite and transporting layers are gaining attention as the key locus that governs solar cell operation and long term performance. The interplay of ionic and electronic processes, along with the asymmetrical architecture of any solar cell, makes the interpretation of electrical measurements always inconclusive. A strategy to progress in relating electric responses, operating mechanisms, and device architecture relies upon simplifying the probing structure. Macroscopic CH3NH3PbBr3 single crystals with symmetrical contacts are tested by means of long-time current transient and impedance spectroscopy. It is observed that interfaces govern carrier injection to (and extraction from) perovskite layers through an inductive (negative capacitance) mechanism with a response time in the range of ∼1–1001–100 s under dark conditions and inert atmosphere. Current transient exhibits a slow recovering after the occurrence of an undershoot, signaling a complex carrier dynamics which involves changes in surface state occupancy

Diamond-based electrodes for organic photovoltaic devices

The present paper demonstrates the possibility of replacing indium–tin oxide (ITO) with heavily boron-doped diamond (BDD). Plasma Enhanced Chemically Vapor Deposited BDDs layers of various thicknesses were prepared containing various boron concentrations in a gas phase. The dependence of the above-mentioned parameters on the optical and electrical properties of each BDD was studied in order to achieve optimal conditions for the effective application of diamond electrodes in organic electronics as a replacement for ITO. Bulk-heterojunction polymer–fullerene organic solar cells were fabricated to test the potency of BDD application in photovoltaic devices. The obtained results demonstrated the possibility of the aforementioned application. Even though the efficiency of BDD-based devices is lower compared to those using regular ITO-based architecture, the relevant issues were explained

Reversible Formation of Gold Halides in Single‐Crystal Hybrid‐Perovskite/Au Interface upon Biasing and Effect on Electronic Carrier Injection

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

Morphology versus Vertical Phase Segregation in Solvent Annealed Small Molecule Bulk Heterojunction Organic Solar Cells

The deep study of solvent annealed small molecules bulk heterojunction organic solar cells based on DPP(TBFu)2 : PC60BM blend is carried out. To reveal the reason of the solvent annealing advantage over the thermal one, capacitance-voltage measurements were applied. It was found that controlling the vertical phase segregation in the solar cells a high fullerene population in the vicinity of the cathode could be achieved. This results in increase of the shunt resistance of the cell, thus improving the light harvesting efficiency

Charge transport in highly efficient iridium cored electrophosphorescent dendrimers

Electrophosphorescent dendrimers are promising materials for highly efficient light-emitting diodes. They consist of a phosphorescent core onto which dendritic groups are attached. Here, we present an investigation into the optical and electronic properties of highly efficient phosphorescent dendrimers. The effect of dendrimer structure on charge transport and optical properties is studied using temperature-dependent charge-generation-layer time-of-flight measurements and current voltage (I-V) analysis. A model is used to explain trends seen in the I-V characteristics. We demonstrate that fine tuning the mobility by chemical structure is possible in these dendrimers and show that this can lead to highly efficient bilayer dendrimer light-emitting diodes with neat emissive layers. Power efficiencies of 20 lm/W were measured for devices containing a second-generation (G2) Ir(ppy)(3) dendrimer with a 1,3,5-tris(2-N-phenylbenzimidazolyl)benzene electron transport layer. (C) 2004 American Institute of Physics