Improving the efficiency of ZnO-based dye-sensitized solar cells by Pr and N co-doping

Pr and N co-doped ZnO (Pr: N: ZnO, doping concentration: 1 mol% Pr, 0.36 mol% N) was synthesized using an annealing method under an atmosphere of NH3 gas in a custom stainless steel autoclave. Scanning electron microscopy (SEM) was used to characterize the morphology of Pr: N: ZnO. The structure and chemical composition of the material were characterized using X-ray diffraction analysis (XRD) and X-ray photoelectron spectroscopy (XPS). The results demonstrated that Pr: N: ZnO maintained a hexagonal wurtzite structure, and that Pr and N atoms were successfully incorporated into the lattice of ZnO. The co-doping of Pr and N has a significant influence on the optical properties of ZnO. UV-visible absorption spectroscopy (UV-vis) showed that Pr and N co-doping led to a red shift of the absorption edge of ZnO into the visible-light region. UV-visible absorption spectroscopy and surface photovoltage spectroscopy (SPS) demonstrated that the band gap of ZnO was narrowed with the dopant atoms generating impurity sub-bands. The incident photon-to-current conversion efficiency (IPCE) spectra demonstrated that Pr and N co-doping could successfully improve the light harvesting of a DSSC. The transient photovoltage (TPV) indicated that Pr and N co-doping increased the rate of charge separation and the electron lifetime. A dye-sensitized solar cell with Pr: N: ZnO as the anode exhibited a short-circuit photocurrent density as high as 13.84 mA cm(-2), an open-circuit photovoltage of 590 mV, a fill factor of 0.63, and an overall light conversion efficiency of 5.2% under standard global AM 1.5 solar irradiation conditions.