A Donor-Supply Electrode (DSE) for Colloidal Quantum Dot Photovoltaics

Ghada I. Koleilat, Xihua Wang, Andre J. Labelle, Alexander H. Ip, Graham H. Carey, Armin Fischer, Larissa Levina, Lukasz Brzozowski, Edward H. Sargent

Research output: Contribution to journalArticlepeer-review

24 Scopus citations

Abstract

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.
Original languageEnglish (US)
Pages (from-to)5173-5178
Number of pages6
JournalNano Letters
Volume11
Issue number12
DOIs
StatePublished - Dec 14 2011
Externally publishedYes

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