Nontechnical Description
The sun represents the most abundant potential source of pollution-free energy on earth. Solar cells for the conversion of sunlight to electricity, also known as photovoltaic (PV) solar cells, suffer from a variety of complicated electrical processes during their operation that lower the overall solar energy conversion efficiency. This project will develop and use a novel technique based on magnetic field measurements to probe these electrical processes at material interfaces within two major classes of photovoltaic devices, organic polymer based photovoltaic (OPV) solar cells, and perovskite material based semiconductor solar PV cells, while these devices are in actual operation. OPV devices offer promise because they can be made from relatively inexpensive organic polymer materials, and perovskite materials offer promise because they are obtained from minerals abundant in the earth?s crust and have relatively high solar energy conversion efficiencies. Fundamental understanding of the useful and non-useful photovoltaic processes at material interfaces within these PV materials will suggest materials synthesis pathways and device engineering that can potentially lead to increased solar energy conversion efficiency in both PV device classes. The proposed activities will also offer interdisciplinary opportunities to enhance class teaching, research training opportunities for students from under-represented groups in science and engineering, and outreach activities for high-school students on the topic of organic polymer based solar cells.
In a photovoltaic (PV) device, when a photon from sunlight is absorbed and converted into an electron-hole pair, there are several loss mechanisms which prevent the charge from being carried away from the device as electric current, resulting in lowered solar energy conversion efficiency. The overall goal of this project is to gain a fundamental understanding of these recombination loss mechanisms at material interfaces though a unique magnetic field measurement technique. Specifically, the project will make measurements of magnetic field induced photocurrent and photo-induced capacitance to probe the binding energy and charge transfer states of the dynamic donor/acceptor interface in excitonic organic polymer based photovoltaic (OPV) devices, and the electrode interface non-excitonic perovskite thin-film photovoltaic devices respectively, using real operating devices under device operating conditions. The proposed research will gain insights on how to tune the electron-hole binding energies at the donor/acceptor interface for excitonic, bulk hetero-junction OPV devices through control of polarization and energy parameters, and on how to enhance the charge collection at the electrode interface in non-excitonic perovskite thin-film PV devices through dielectric effects. The research plan will focus on three tasks, including materials processing and device engineering to tune polarization and energy parameters at donor/acceptor and electrode interfaces, experimental studies on the useful and non-useful photovoltaic processes occurring at donor/acceptor and electrode interfaces, and finally, elucidation on the key parameters that control the electron-hole binding energies at the donor/acceptor interface and the charge collection at electrode interfaces. Fundamental understanding of the useful and non-useful photovoltaic processes at dynamic donor/acceptor and electrode interfaces will suggest materials synthesis pathways and device engineering that can potentially lead to increased solar energy conversion efficiency in both excitonic, bulk-hetero-junction OPVs and non-excitonic perovskite thin-film PV devices. With respect to education and broadening participation, the proposed activities will also offer interdisciplinary opportunities to enhance class teaching, research training opportunities for students from under-represented groups in science and engineering, and outreach activities for high-school students on the topic of organic polymer based solar cells.
