Optical Resonance Engineering for Infrared Colloidal Quantum Dot Photovoltaics

We report optically enhanced infrared-harvesting colloidal quantum dot solar cells based on integrated Fabry–Perot cavities. By integrating the active layer of the photovoltaic device between two reflective interfaces, we tune its sensitivity in the spectral region at 1100–1350 nm. The top and bottom electrodes also serve as mirrors, converting the device into an optical resonator. The front conductive mirror consists of a dielectric stack of SiN x and SiO 2 with a terminal layer of ITO and ZnO in which current can flow, while the back mirror consists of a highly reflective gold layer. Adjusting the reflectivity and central wavelength of the front mirror as well as the thickness of the active layer allowed increases in absorption by a total of 56% in the infrared, leading to a record external quantum efficiency of 60% at 1300 nm. This work opens new avenues toward low-cost, high-efficiency rear-junction photovoltaic harvesters that add to the overall performance of silicon solar cells.