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We report on inorganic CsPbBr 3 solar cells with very high open circuit voltages and excellent environmental stability. The cells were fabricated using vapor deposition. We show that by using an interfacial n-doped CdS (CdS:In) layer between the cell TiO2, we can obtain voltages of ∼1.68 V, the highest ever reported in vapor deposited CsPbBr3 material. A surprising phenomenon was that the crystal structure of the material, and the apparent bandgap, changed when a thicker CdS:In layer was used as the n layer. We also show that there is little environmental degradation in performance for a cell kept for 600 hours in room air, and even for a cell kept at 200 °C for 24 hours in air. The cells were deposited using sequential deposition in vacuum followed by anneals at 450 °C. We study both organic p layers (P3HT) and inorganic p layers (paste coated C). 

We report on the properties and stability of inorganic perovskite CsPbBr3 fabricated using vapor deposition. We have obtained the highest voltage ever recorded, exceeding 1.6V, in this material. The material was deposited using vapor deposition process, followed by post-deposition anneal at 450 C. Both layer by layer, and sequential anneal processes were sued for growing the material. After growth and anneals, the material was tested for thermal stability at temperatures of 300 C, and the x-ray data showed that there was no degradation of the material even at this high temperature. n-i-p superstrate devices were fabricated on FTO substrates coated with either TiO2 or n-CdS. The p layer was P3HT or PTAA. The devices showed an open-circuit voltage of 1.62V, the highest ever reported in this material. The devices were exposed to humid room air for 25 days, and showed no degradation at all in its performance. Detailed material measurements such as subgap quantum efficiency and deep defects were measured. The Urbach energy for valence band tails is found to be 22 meV and mid-gap defect density in the range of few 1015/cm3. 

CdSe is potentially an important material for making tandem junction solar cells with Si and CIGS. Thermodynamic calculations reveal the potential Shockley-Queisser efficiency of such a tandem cell to be in the 45% range. CdSe has the optimum bandgap (1.72eV) for a tandem cell with Si. In this paper, we show that this material system is indeed capable of achieving good electronic properties and reasonable devices can be made in the material. We report on fabricating CdSe materials and heterojunction CdSe solar cells in both superstrate and substrate configurations on FTO/glass and metal substrates. CdSe layer was deposited using thermal evaporation and then was post-treated with CdCl2 to enhance the grainsize and passivate grain boundaries. The device was an ideal heterojunction structure consisting of glass/FTO/n+CdS/ n-CdSe/p organic layer/NiO/ITO. The n+ CdS layer acted to prevent hole recombination at the n+/n interface, and the p organic layer (such as PEDOT:PSS or P3HT) acted to prevent electron recombination at the p+/n interface. The NiO layer was deposited on top of the organic layer to prevent decomposition of the organic layer during ITO deposition. World-record open-circuit voltages exceeding 800 mV and currents of ~15 mA/cm2 were obtained in devices. Detailed material measurements such as SEM revealed large grain sizes approaching 8 micrometer in some of the films after grain enhancement. Optical measurements and QE measurements show the bandgap to be 1.72 eV. XPS measurements showed the CdSe film to be n type. Space-charge limited current was used to measure electron mobilities which were in the range of 1-2 cm2/V-s. Capacitance spectroscopy showed the doping densities to be in the range of a few x 1015/cm3. For substrate devices, the quantum efficiency obtained was in the 90% range. 

We report on the growth, grain enhancement, doping, and electron mobility of cadmium selenide (CdSe) thin films deposited using the thermal evaporation method. The optical measurement shows CdSe is a direct bandgap material with an optical bandgap (Egap) of 1.72 eV. CdSe thin films were deposited on fluorine doped tin oxide glass substrates with different thicknesses, and grain size and mobility were measured on the films. CdCl2 was deposited on the films, and the films were subjected to high temperature treatment for several hours. It was found that both grain sizes increased significantly after CdCl2 treatment. The mobility of electrons was measured using the space charge limited current technique, and it was found that the mobility increased significantly after CdCl2 treatment. It was discovered that postdeposition selenization further improved the electrical properties of CdSe thin films by increasing the electron mobility-lifetime product and the photo/dark conductivity ratio. CdSe films after postselenization also showed significantly lower values for midgap states and Urbach energies for valence band tail states.