Tandem Solar Cells Using Perovskites, Silicon and CIGSAuditorium between Bldg. 4&5
Abstract: The efficiency of perovskite solar cells has soared from a few percent to over 17% in the last 2 years. They are very attractive for multijunction solar cell applications because the bandgap of perovskite semiconductors can be easily tuned in the range of 1.55 to 2.2 eV and the open circuit voltage of the cells is large. We have made highly efficient semitransparent perovskite solar cells using silver nanowire meshes as the top electrode. These cells can be used in combination with either silicon or copper indium galliumdiselenide solar cells to make four-terminal and two-terminal tandems. We will also present detailed characterization of perovskite semiconductors made with different processing conditions to show what needs to be done to minimize recombination and make the solar cells stable.
Progress in understanding what it will take to make organic solar cells more than 15% efficient and stable
Abstract: In the first part of the talk a new model will be presented that shows how much the voltage of organic solar cells depends on factors such as the degree of intermixing between the donor and acceptor semiconductors, the binding energy of the charge transfer state, the lifetime of the charge transfer state and the degree of energetic disorder.In the 2nd part of the talk results from a device simulator will be used to show that it is now possible to accurately predict the performance of many organic solar cells and that it will be necessary to use materials with the charge carrier mobility of at least 10^-2 cm^2/Vs in order to achieve high fill factors in devices that are thick enough to absorb almost all of the light. In the final part of the talk the mechanisms of degradation in organic solar cells will be presented. We will show that it is possible to prevent Long-term degradation by using materials with high glass transition temperatures and protecting films from oxygen and water. We will show that burn in degradation can largely be eliminated by using crystalline materials.
Michael D. McGehee is a Professor in the Materials Science and Engineering Department and a Senior Fellow of the Precourt Institute for Energy atStanford. His research interests are patterning materials at the nanometer length scale, semiconducting polymers and solar cells. He has taught courses on nanotechnology, nanocharacterization, organic semiconductors, polymer science and solar cells. He received his undergraduate degree in physics from Princeton University and his PhD degree in Materials Science from the University of California at Santa Barbara, where he did research on polymer lasers in the lab of Nobel Laureate Alan Heeger. He won the 2007 Materials Research Society Outstanding Young Investigator Award. He is a technical advisor to NextTint, Next Energy, PLANT PV, Plextronics and Sinovia.