Tandem colloidal quantum dot solar cells employing a graded recombination layer

Tuning of the electronic bandgap in colloidal quantum dots (CQDs) by changing their size enables the spectral response of CQD-based photodetectors 1 , 2 , 3 , 4 , 5 and photovoltaic 6 , 7 , 8 , 9 , 10 , 11 , 12 devices to be tailored. Multi-junction solar cells made from a combination of CQDs of differing sizes and thus bandgaps are a promising means by which to increase the energy harvested from the Sun's broad spectrum. Here, we report the first CQD tandem solar cells using the size-effect tuning of a single CQD material, PbS. We use a graded recombination layer to provide a progression of work functions from the hole-accepting electrode in the bottom cell to the electron-accepting electrode in the top cell, allowing matched electron and hole currents to meet and recombine. Our tandem solar cell has an open-circuit voltage of 1.06 V, equal to the sum of the two constituent single-junction devices, and a solar power conversion efficiency of up to 4.2%. Researchers report a colloidal quantum-dot solar cell that features two junctions, each designed to absorb and convert different spectral bands of light within the solar spectrum. The device offers a power conversion efficiency of 4.2% and an open circuit voltage of 1.06 V.