Nitrogen doping of TiO2 and annealing treatment of photoanode for enhanced solar cell performance.

Mild doping of nitrogen (N) in TiO 2 followed by an optimized aerial annealing treatment of CdS quantum dot (QD) sensitized photoanode resulted in efficient electron transfer and low recombination rates for the corresponding quantum dot solar cell (QDSC). Nitrogen doping passivates the surface defects in TiO 2 , reduces the density of recombination centers, and promotes electron injection into the current collector. N-doping also modifies the electronic band structure of TiO 2 and reduces the band gap from 3.17 to 2.91 eV. Therefore in the QDSC with the N-TiO 2 /CdS photoanode, both N-TiO 2 and CdS, undergo charge separation upon illumination thereby producing a higher photocurrent compared to the undoped-TiO 2 /CdS based QDSC. N-doping also increased the redox activity of TiO 2 , allowing facile ion and electron transport across its cross-section which is advantageous for solar cell performance. Optimal annealing temperature of 150 °C for the N-TiO 2 /CdS or TiO 2 /CdS photoanode restricted the back electron movement effectively, and imparted a significantly enhanced power conversion efficiency (PCE) to the N-TiO 2 /CdS@150 °C/polysulfide gel/C-fabric- solar cell, greater by 55% compared to its unannealed counterpart. Lowered average excited electron lifetime, increased-incident photon-to-current conversion efficiency, recombination resistance and photovoltage decay response time, confirm the ability of the annealed photoanodes to undergo enhanced charge separation contrasting with the unannealed photoanode. This first time study relies on two simple approaches of nitrogen doping and annealing treatment to achieve considerably improved photovoltaic parameters, and opens up realistic possibilities for commercialization of QDSCs. Image 1 • Nitrogen (N) doping of TiO 2 passivates the surface defects. • N-doped TiO 2 produces additional photocurrent, by undergoing charge-separation. • N-doping enhances the redox activity of the oxide, promotes electron/ion transport. • Annealing treatment at 150 °C enables facile charge transfer at the quantum dot/oxide interface. • Efficiency of the solar cell: N-TiO 2 /CdS@150 °C/polysulfide gel/C-fabric is 4.58%. [ABSTRACT FROM AUTHOR]