Michael Kulbak

Learn More
Low-cost solar cells with high VOC, relatively small (EG - qVOC), and high qVOC/EG ratio, where EG is the absorber band gap, are long sought after, especially for use in tandem cells or other systems with spectral splitting. We report a significant improvement in CH3NH3PbBr3-based cells, using CH3NH3PbBr3-xClx, with EG = 2.3 eV, as the absorber in a(More)
Hybrid organic-inorganic lead halide perovskite photovoltaic cells have already surpassed 20% conversion efficiency in the few years that they have been seriously studied. However, many fundamental questions still remain unanswered as to why they are so good. One of these is "Is the organic cation really necessary to obtain high quality cells?" In this(More)
Direct comparison between perovskite-structured hybrid organic-inorganic methylammonium lead bromide (MAPbBr3) and all-inorganic cesium lead bromide (CsPbBr3), allows identifying possible fundamental differences in their structural, thermal and electronic characteristics. Both materials possess a similar direct optical band gap, but CsPbBr3 demonstrates a(More)
High band gap, high open-circuit voltage solar cells with methylammonium lead tribromide (MAPbBr3) perovskite absorbers are of interest for spectral splitting and photoelectrochemical applications, because of their good performance and ease of processing. The physical origin of high performance in these and similar perovskite-based devices remains only(More)
Using several metals with different work functions as solar cell back contact we identify majority carrier type inversion in methylammonium lead bromide (MAPbBr3, without intentional doping) as the basis for the formation of a p-n junction. MAPbBr3 films deposited on TiO2 are slightly n-type, whereas in a full device they are strongly p-type. The charge(More)
All photovoltaic device efficiencies are limited by the `threshold' process inherent in how photovoltaic devices work: a photon above a certain energy level is required to excite an electron that will later be extracted as electrical current. This sets a limit to the efficiency of solar power conversion to electricity of a “single threshold”(More)
We report valence and conduction band densities of states measured via ultraviolet and inverse photoemission spectroscopies on three metal halide perovskites, specifically methylammonium lead iodide and bromide and cesium lead bromide (MAPbI3, MAPbBr3, CsPbBr3), grown at two different institutions on different substrates. These are compared with theoretical(More)
  • 1