Improved performance of hybrid ZnO/polymer solar cell via construction of hierarchical nanostructures and surface modification of ZnO

Photovoltaic performance of hybrid ZnO/polymer solar cell is enhanced through the addition of ZnO nanoparticles (NPs) onto ZnO nanorod arrays (NRs), and surface modification with squaraine (Sq). The cluster of NPs at the end of NRs is formed during spin coating process but poly(3-hexylthiophene) (P3HT), as electron donor, is able to infiltrate into the rod-to-rod space, as confirmed by zero-loss energy-filtered transmission electron microscopy (zero-loss EFTEM) observation. Due to the increase in ZnO/P3HT interface area, the NP-coated NR device shows power conversion efficiency ( PCE ) of 0.49%, which is higher than that of the pristine ZnO NRs/P3HT one (0.26%). Further improvement is achieved by the adsorption of Sq onto the NP-coated ZnO NR surfaces. After the dye-modification, the P3HT infiltration is poorer than the unmodified one. This leads to the ZnO NRs/Sq/air interface, where exciton separation does not occur. However, due to the large surface area of NPs and the light absorption in near IR region of Sq, the PCE increased to 1.37% with relatively higher short circuit current density as compared with the case without the NPs and Sq.