Versatile use of ZnO interlayer in hybrid solar cells for self-powered near infra-red photo-detecting application

We investigate the possibility of shifting the absorption peak of the hybrid solar cell into the red to near infra-red (NIR) region using a ZnO optical spacer. Poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta [2,1-b; 3,4-b′]dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT) exhibits a 700 nm wavelength peak absorption and is a low-bandgap polymer. Zinc oxide (ZnO) was used as an n-type semiconducting electron acceptor. The efficiency was enhanced by introducing a ZnO optical spacer layer. A finite-difference time-domain simulation was performed with the aim to extract the largest simulated short-circuit current density from the hybrid photovoltaic cell structure. Via the simulation, we also tuned the ZnO thickness to make the solar cell sensitive to the NIR wavelengths and thus obtained the optimal structures for various active layer thicknesses suitable for NIR absorption applications. This study aims to demonstrate the applicability of the PCPDTBT:ZnO hybrid solar cell as a multi-functional NIR absorber cum solar cell which has potential applications in energy harvesting window coating, NIR photodetector, and tandem solar subcell through the use of a ZnO optical layer to control the light-induced electric field distribution inside the device structure.