Ebook: Materials Challenges for CdTe and CuInSe2 Photovoltaics

The record laboratory cell (☻1 cm2 area) efficiency for thin - film cadmium telluride(CdTe) is 16.5%, and that for a copper indium diselenide (CuInSe2) thin - film alloyis 19.5%. Commercially produced CdTe and CuInSe2 modules (0.5-1 m2 area) haveefficiencies in the 7-11% range. Research is needed both to increase laboratory cellefficiencies and to bring those small - area efficiencies to large - area production. Increasesin laboratory CdTe cell efficiency will require increasing open - circuit voltage, whichwill allow cells to harvest more energy from each absorbed photon. This will requireextending the minority carrier lifetime from its present τ ♦ 2 ns to τ ♣ 10 ns and in -creasing hole concentration in the CdTe beyond 1015 cm2, which appears to be limited bycompensating defects. Increasing laboratory CuInSe2 - based cell efficiency significantlybeyond 19.5% will also require increasing the open - circuit voltage, either by increasingthe bandgap, the doping level, or the minority carrier lifetime. The photovoltaic cells incommercial modules occupy tens of square centimeters, and both models and exper -iments have shown that low - performing regions in small fractions of a cell can signif i -cantly reduce the overall cell per form ance. Increases in commercial module efficiencywill require control of ma te rials properties across large deposition areas in a high -throughput environment to minimize such non - uniformities. This ar ticle discusses ap -proaches used and research needed to increase the ultimate efficiencies of CdTe - andCuInSe2 - based devices and translate these gains to commercial photovoltaic modules.