The highest-performing colloidal quantum dot (CQD) photovoltaics (PV) reported to date have relied on high-temperature (>500°C) annealing of electron-accepting TiO 2. Room-temperature processing reduces energy payback time and manufacturing cost, enables flexible substrates, and permits tandem solar cells that integrate a small-bandgap back cell atop a low-thermal-budget larger-bandgap front cell. Here we report an electrode strategy that enables a depleted-heterojunction CQD PV device to be fabricated entirely at room temperature. We find that simply replacing the high-temperature-processed TiO 2 with a sputtered version of the same material leads to poor performance due to the low mobility of the sputtered oxide. We develop instead a two-layer donor-supply electrode (DSE) in which a highly doped, shallow work function layer supplies a high density of free electrons to an ultrathin TiO 2 layer via charge-transfer doping. Using the DSE we build all-room-temperature-processed small-bandgap (1 eV) colloidal quantum dot solar cells having 4% solar power conversion efficiency and high fill factor. These 1 eV bandgap cells are suitable for use as the back junction in tandem solar cells. The DSE concept, combined with control over TiO 2 stoichiometry in sputtering, provides a much-needed tunable electrode to pair with quantum-size-effect CQD films. © 2011 American Chemical Society.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledged KAUST grant number(s): KUS-11-009-21
Acknowledgements: This publication is based in part on work supported by an award (no. KUS-11-009-21) made by King Abdullah University of Science and Technology (KAUST), by the Ontario Research Fund Research Excellence Program, by the Natural Sciences and Engineering Research Council (NSERC) of Canada, and by Angstrom Engineering and Innovative Technology. The authors would also like to acknowledge the assistance of Ratan Debnath, Huan Liu, Elenita Palmiano, Remigiusz Wolowiec, and Damir Kopilovic as well as the assistance of Mark T. Greiner with UPS/XPS measurement. G.I.K. acknowledges NSERC support in the form of Alexander Graham Bell Canada Graduate Scholarship.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.