Template assisted nanoporous TiO2 nanoparticles: The effect of oxygen vacancy defects on photovoltaic performance of DSSC and QDSSC

Abstract We present a detailed study on the photovoltaic performance of dye and quantum dot (QD) sensitized solar cells fabricated using nanoporous TiO 2 photoanodes prepared by a template approach. Nanoporous TiO 2 particles (TNPO) are prepared by sol-gel method using dextran (TNPO-D) and glucose (TNPO-G) as templates. The decomposition of templating agents during calcination introduces nanopores (∼10 nm) in TiO 2 nanoparticles as evidenced from the HRTEM studies. Oxygen vacancies are also introduced in TiO 2 nanoparticles due to prevailing reducing ambient during decomposition. Oxygen vacancy (V O ) related defects are evidenced from EPR spectra from a strong absorption signal observed at g-value of 1.994 related to Ti 3+ -V O -Ti 3+ defect sites. The defect concentration estimated from EPR spectra is found to be ∼5 to 15 times larger for nanoporous TiO 2 particles compared to Degussa P25-TiO 2 . TNPO samples also show enhanced defect level photoluminescence emission. The photovoltaic efficiency (η) and the IPCE of DSSC and QDSSC are strongly influenced by the defect concentration and seen to decrease with increasing V O in TiO 2 nanoparticles. Twofold lower η is found in both DSSC (∼6.38% to 3.66%) and QDSSC (∼1.69% to 0.46%) devices made using nanoporous TiO 2 compared to P25-TiO 2 photoanode solar cells. P25-TiO 2 also shows significant decrease in η when oxygen vacancies are introduced by hydrogen annealing process, which reveal detrimental effect of V O on the photovoltaic properties. EIS studies suggest increased interfacial resistance in solar cells made from nanoporous TiO 2 photoanodes.