Control of charge dynamics by blending ZnO nanoparticles with poly(3-hexylthiophene) for efficient hybrid ZnO nanorods/polymer solar cells

Abstract

Photovoltaic performances of hybrid ZnO nanorods/polymer solar cells have been improved by controlling their charge dynamics through addition of ZnO nanoparticles into poly(3-hexylthiophene) (P3HT) photoactive layer. The inter-rod space of ZnO nanorod substrates is completely filled with the solution-processed ZnO nanoparticles/P3HT blends, forming homogeneous junction among the components. The optimum PCE of 1.020 % has been achieved from the device with 13 vol % ZnO nanoparticles loaded. The enhancement in external quantum efficiency has been also observed, indicating the improved excitons separation at the ZnO/P3HT interface. The information on charge dynamics in the system has been investigated by electrochemical impedance spectroscopy. It has been found that the additional space-charge layer formed at the ZnO nanoparticles-contact electrode interface is a reason behind the improvement of open-circuit voltage. Moreover, the formation of ZnO nanoparticles domain extending across the active layer and the percolation path for charge carriers promotes charge transport by reducing transit time of the carriers, extending charge carrier lifetime and enhancing the charge transfer at the ZnO/P3HT interface. Interestingly, it has been found that charge transport in the devices does not limit the device performances, even for the 400-nm-thick active layer.

Photophysical Behaviors at Interfaces between Poly(3-Hexylthiophene) and Zinc Oxide Nanostructures

“…It was observed that the uorescence decayed faster as the concentration of ZnO NPs increases in Sample B, consistent with the results in Ref. 7).…”

“…Poly(3-hexylthiophene) (P3HT) is a conventional conjugated polymer applied in OSC as donor in the active layer 4,5) . As a candidate of inorganic semiconductor, ZnO is famous for its multiple nanostructures, which have high carrier mobility and ambient stability 6,7) . Photoinduced electron transfer occurs at the interface between the polymer (donor) and the inorganic semiconductor (acceptor) and results in ef cient charge separation.…”

“…In priori studies, generally there are two categories of P3HT and ZnO interfaces: I. ZnO nanostructures blended with P3HT as the active layer; II. P3HT as active layer on top of ZnO nanostructures as buffer layer 7,8) . For applications in solar cells as well as others mentioned above, a detailed investigation of the photophysical behavior of P3HT upon excitation is a critical research point for optimizing device functions.…”