Improved Photovoltaic Performance via Downconversion and Upconversion

Despite decades of research, solar cell efficiencies struggle to get higher than 25%. This is due to two fundamental losses in the device: thermalization of high energy photons and transmission of low energy photons. To combat these losses, we first utilize singlet exciton fission as a downconverting layer. Singlet exciton fission is a process in which a single high energy exciton fissions into two excitons of half the energy. Here, we first demonstrate the potential of singlet fission in an all-organic solar cell. We measure an EQE as high as 126%, breaking the conventional limit of 100%. We demonstrate that low energy excitons generated in the fission material can transfer to a colloidal nanocrystal with 90% efficiency before fluorescing, allowing for optical harvesting. We further utilize colloidal nanocrystals and the organic material rubrene to construct an upconverting layer, allowing for harvesting of infrared light typically invisible to modern photovoltaics. When combined, these layers could increase the power efficiency of a silicon solar cell from 25% to greater than 35%.