Niobium doped zinc oxide nanorods as an electron transport layer for high-performance inverted polymer solar cells.

The wet chemical synthesis, characterization and applications of Nb doped ZnO nanorods in bulk heterojunction inverted polymer solar cells are presented in this paper. Zn1-x Nbx O with x ranging from 0.01 to 0.07 were successfully synthesized using a novel facile solution-processed wet chemical method. The structural and optical properties of the undoped and Nb doped ZnO nanorods were investigated by transmission electron microscopy, X-ray diffraction, UV-visible near infrared, and photoluminescence (PL) spectroscopies. A clear red shift was observed in the absorption spectra of Nb doped samples compared to the undoped ZnO nanorods. The defect emission peak in the PL spectrum of the Nb doped nanorods completely disappeared at the highest dopant concentration of x=0.07. These undoped and Nb doped ZnO nanorods, in amalgamation with PTB7-Th:PC71 BM, were used in the inverted polymer solar cells as an electron transport layer which gives better power conversion efficiencies compared to the pure nanorods.