This invention uses a photoactive element between graphene electrodes to create a photovoltaic device that not only produces electricity from sunlight, but also transmits its infrared energy for use in an attached thermal energy device.
A low cost single bandgap photovoltaic (PV) cell usually has a limited wavelength window with the longer wavelength limit in the visible region. For example, a photovoltaic cell having a single p-n junction with a bandgap of about 1.5 eV uses energy primarily in the visible portion of the solar spectrum up to a wavelength near 825 nm, leaving nearly 42% of the energy in the IR portion of the solar spectrum wasted. The IR portion of the sunlight is primarily turned into heat, which degrades the PV efficiency because of the increased junction temperature. The present invention increases the overall effectiveness and efficiency of a PV cell by allowing the IR energy to be put to use for heating purposes or for further electricity generation in a thermal energy device.
This invention can be used to add thermoelectric energy generation capabilities to standard photovoltaic device applications or to combine photovoltaic and thermal energy capabilities in a single device (e.g., building integrated photovoltaics).
In general, the invention would be configured as an infrared transparent photovoltaic (PV) device coupled to a thermal energy device. The PV device includes two graphene electrodes and a photoactive element between the electrodes. Solar light enters the PV device, but only a portion of the incident solar light will be absorbed and converted to electricity. Plasmonic nanostructures may be added to the electrode to further tune the device to certain wavelengths of light. The remaining light (generally, the IR component) is transmitted through the PV device and the corresponding energy is transferred to the thermal energy device.
This invention can increase the efficiency of PV devices in a typical electricity generation application (e.g., by adding a thermoelectric generator behind the PV to produce more power and reduce system dependence on weather conditions), or it can add functionality to an existing PV or thermal energy application (e.g., by generating electricity in addition to heating a building or heating water).
Conventional approaches to the problems of wasted solar light tend to be costly to implement and often fail to make use of the energy available in IR light. The present invention presents an affordable, efficient solution that provides users with an integrated system capable of performing multiple functions with the same energy input.