Paper EN+NS-WeM1
Sol-gel Prepared Ca Doped ZnO and Its Application in Polymer–Oxide Bilayer Hybrid Solar Cells

Wednesday, November 2, 2011, 8:00 am, Room 209

Conjugated polymer/metal oxide hybrid photovoltaic devices have received considerable attention in recent years due to their potential for scalable, low-cost manufacturing. To improve device efficiency, most research has focused on increasing the fill factor and short circuit current. In this article, calcium doped zinc oxide (Zn_xCa_1-xO) is used as electron acceptor in the hybrid poly(3-hexylthiophene) /Zn_xCa_1-xO bilayer solar cells to modify the band offsets and increase the open circuit voltage. XRD results show the sol-gel prepared Ca doped ZnO films have a hexagonal wurtzite phase with no indication of calcium separation. Atomic force micrographs indicate the Zn_xCa_1-xO surface becomes decorated with interconnected ridges approximately 100 nm in height. The rms surface roughness increases with increasing Ca. The band gap obtained from UV-vis absorption spectra widens from 3.20 to 3.60 eV as the Ca concentration increases from x=0 to x=0.12. The work function of the Zn_xCa_1-xO films measured by Kelvin probe is seen to decrease with increasing Ca composition for values of x up to 0.12, which indicates a decrease in electron affinity. The open circuit voltage of hybrid P3HT/Zn_xCa_1-xO devices increases from 570 mV at x = 0 up to 800 mV for x = 0.10. Work is under way to incorporate Ca doped ZnO nanoparticles into bulk heterojunction solar cells to optimize device efficiency.