Organic solar cells convert sunlight into electricity. The first step is that the organic solar cell must absorb light. This absorbed light adds energy into the material, causing the electrons in the material to increase their energy and move through the material, leaving behind a hole. Second, electrons must travel to a region where they can be collected by an acceptor material, lowering their energy (i.e., the donor-acceptor interface, see Figure 1). Once the electrons are collected, they can be extracted to give a current, or they can remain in the device to give rise to a voltage. The electrons that leave the organic solar cell as current can deliver their energy to whatever is connected to the circuit.
Figure 1. Illustration of how an organic solar cell works. (1) Light absorption and formation of an exciton (electron-hole pair); this step is followed by the promotion of an electron into the lowest unoccupied molecular orbital (LUMO) of an electron donor semiconductor (i.e., pentacene molecule); (2) electron transfer from the LUMO of the electron donor semiconductor to the electron acceptor semiconductor (i.e., C60 molecule); and (3) subsequent transport of the electrons to the electrodes. Note: HOMO is the Highest Occupied Molecular Orbital.