EAGER: TDM solar cells: High Efficiency Perovskites and CuInSe (CIS) Tandem Solar cells

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Abstract:Non-technical:Si is the dominant photovoltaic technology used around the world. These solar cells are assembled together to produce solar panels. They represent more than 90% of the solar panel market. The Si crystalline solar cells have demonstrated a maximum photovoltaic solar energy conversion efficiency of about 25% and this conversion efficiency has not improved very much over the last 10 years. On the other hand, tandem solar cells, where one utilizes a stack of two different materials with different band gaps, can lead to a sizable increase in the energy efficiency of solar cells, which would lead to a reduced number of required solar panels to generate the same amount of energy. The project is based on a solar cell made up of a thin layer of perovskite and a thin layer of copper-indium di-selenide (CIS) monolithically stacked together for a total thickness of order 2.5-3 µm, with an expected energy conversion efficiency approaching 30%. These solar cells would allow a quantum leap in energy conversion efficiency as compared to crystalline silicon solar cells. They would also allow the realization of flexible solar cells for many low cost applications. The tandem solar cell uses a chalcogenide material made up of three elements: Cu, In, and Se but does not use Ga as is typically done for single junction CIGS solar cell. The advantage of this approach is that CIS has a smaller bandgap than CIGS and this allows collecting photons over a larger wavelength range and therefore leads to a higher conversion efficiency. In addition, the second material used in the tandem cell is CH3NH3Pb (I1-xBrx)3, a material which is stable. On the contrary, if one would use CIGS as the low bandgap material, the required CH3NH3Pb (I1-xBrx)3 material would need to use a non-stable concentration of bromide. Both of these single junction solar cells have already been made in the Principal Investigator's laboratory with high performance. The challenge is to monolithically integrate both materials in an efficient tandem solar cell.Technical description:Both state-of-the-art CH3NH3PbI3 perovskite and Copper Indium Selenide (CIS) solar cells developed in our laboratory will be used to implement a high performance tandem cell with a predicted efficiency above 30% at one-sun illumination. The band gap of CIS (no gallium) solar cells is 1.0 eV and is more adapted than the traditional CIGS solar cell or silicon based solar cells with a bandgap of 1.15 eV to realizing high efficiency tandem solar cells based on perovskites. The reason is that the most efficient tandem solar cell for a material with a bandgap of 1.15 eV is a material with a bandgap of 1.7-1.8 eV. CH3NH3Pb(I1-xBrx)3 can be made to have a bandgap of 1.74 eV but has been found to be unstable. For a material with a bandgap of 1.0 eV, the optimum higher bandgap is 1.64 eV and corresponds to a proportion of bromide where the perovskite layer CH3NH3Pb(I1-xBrx)3 is stable. In this project, high efficiency, environmentally stable, CH3NH3Pb(I1-xBrx)3 /CIS tandem solar cells will be developed. Both mechanically stacked and monolithic perovskite/CIS tandem solar cells will be studied. The approach leverages thin film solar cell technology that has been validated in industry and opens up the way to highly efficient low cost solar cells.