The solar energy storage polymer lithium ion battery works on the principle that when photons of the right energy are shone through the ITO glass onto the photosensitive layer, the donor or acceptor material on the photosensitive layer absorbs the photons and excitons appear, then the excitons diffuse to the donor/acceptor interface where charge separation occurs, resulting in holes on the donor and electrons on the acceptor. The holes then pass along the donor to the anode and are collected by the anode, and the electrons pass along the receptor to the cathode and are collected by the cathode, resulting in photocurrent and photovoltage.
Schematic diagram of the photovoltaic effect of a solar polymer cell based on the donor/acceptor approach
The light absorption properties of the donor and acceptor materials, the hole mobility of the donor, the electron mobility of the acceptor and the position of the highest occupied orbital (HOMO) and lowest empty orbital (LLUMO) energy levels have a significant impact on the performance of organic photovoltaic devices. With regard to the electron energy levels, the donor material should have relatively high LUMO and HOMO energy levels, while the acceptor material should have low LUMO and HOMO energy levels, so as to ensure that the electrons at the LUMO energy level of the exciton in the donor can be spontaneously transferred to the LUMO energy level of the acceptor at the donor/acceptor interface, and the holes at the HOMO energy level of the exciton in the acceptor can be spontaneously transfer to the HOMo energy level of the donor, thus achieving charge separation.
In short, the photovoltaic conversion of polymer solar cells can be simplified to the following four processes.
Diagram of the working mechanism of a solar polymer cell
(1) excitons appear when the donor is excited by light.
(2) exciton diffusion to the D/A interface
(3) The exciton separates at the D/A interface to form an electron-hole pair
(4) Free carriers are transported and collected at the external electrode.