The preparation of a Eu3+-doped ZnO bi-functional layer and its application in organic photovoltaics

Abstract

Recently, spectra conversion has been used to minimize energy loss in photovoltaic devices. In this work, we explore the development of a novel Eu3+-doped ZnO bi-functional layer for use in organic solar cells. The bi-functional layer acts as both a spectra conversion and an electron transporting layer. Compared to conventional spectra conversion layers, it has a simpler device structure, is easier to fabricate, and has a wider spectrum-sensitized region. A series of Eu3+-doped ZnO nanocrystals were synthesized using the simple solution route. X-ray powder diffraction patterns (XRD), transmission electron microscopy (TEM), and UV-visible absorbance spectra were used to characterize the obtained ZnO nanocrystals. The results reveal that the size and bandgap of ZnO nanocrystals can be controlled through regulation of the doping concentration of Eu3+ ions. The energy transfer of ZnO → Eu3+ is observed by photoluminescence (PL) spectra. At a bandgap excitation of around 300–400 nm, a typical emission band from the Eu3+ is obtained. By employing the Eu3+- doped ZnO nanocrystals as a buffer layer in a P3HT:PC61BM bulk heterojunction device, the obtained performance is similar to the undoped ZnO device, indicating that the electrical properties of ZnO are not affected by Eu3+ doping. Due to the down-conversion energy transfer between ZnO and Eu3+, the external quantum efficiency of the ZnO:Eu3+ device at 300–400 nm is higher than that of the pure ZnO device, which subsequently leads to an increase in short circuit current density (JSC). This work proves that it is possible to improve the solar spectrum response in the ultraviolet region of organic solar cells effectively by incorporating the bi-functional layer.