title: Low-temperature noninjection approach to homogeneously-alloyed PbSe(x)S(1-x) colloidal nanocrystals for photovoltaic applications.
abstract: Homogeneously alloyed PbSe(x)S(1-x) nanocrystals (NCs) with their excitonic absorption peaks in wavelength shorter than 1200 nm were developed for photovoltaic (PV) applications. Schottky-type solar cells fabricated with our PbSe₀.₃S₀.₇ NCs as their active materials reached a high power conversion efficiency (PCE) of 3.44%, with an open circuit voltage (V(oc)) of 0.49 V, short circuit photocurrent (J(sc)) of 13.09 mA/cm², and fill factor (FF) of 0.54 under Air Mass 1.5 global (AM 1.5G) irradiation of 100 mW/cm². The syntheses of the small-sized colloidal PbSe(x)S(1-x) NCs were carried out at low temperature (60 °C) with long growth periods (such as 45 min) via a one-pot noninjection-based approach in 1-octadecene (ODE), featuring high reaction yield, high product quality, and high synthetic reproducibility. This low-temperature approach employed Pb(oleate)₂ as a Pb precursor and air-stable low-cost thioacetamide (TAA) as a S source instead of air-sensitive high-cost bis(trimethylsilyl)sulfide ((TMS)₂S), with n-tributylphosphine selenide (TBPSe) as a Se precursor instead of n-trioctylphosphine selenide (TOPSe). The reactivity difference of TOPSe made from commercial TOP 90% and TBPSe made from commercial TBP 97% and TBP 99% was addressed with in situ observation of the temporal evolution of NC absorption and with ³¹P nuclear magnetic resonance (NMR). Furthermore, the addition of a strong reducing/nucleation agent diphenylphosphine (DPP) promoted the reactivity of the Pb precursor through the formation of a Pb-P complex, which is much more reactive than Pb(oleate)₂. Thus, the reactivity of TBPSe was increased more than that of TAA. The larger the DPP-to-Pb feed molar ratio, the more the Pb-P complex, the higher the Se amount in the resulting homogeneously alloyed PbSe(x)S(1-x) NCs. Therefore, the use of DPP allowed reactivity match of the Se and S precursors and led to sizable nucleation at low temperature so that long growth periods became feasible. The present study brings insight into the formation mechanism of monomers, nucleation/growth of colloidal composition-tunable NCs, and materials design and synthesis for next-generation low-cost and high-efficiency solar cells.
authors.affiliation: Steacie Institute for Molecular Sciences, National Research Council of Canada , Ottawa, Ontario K1A0R6, Canada. kui.yu@nrc.ca
authors.forename: Kui
authors.initials: K
authors.lastname: Yu
authors.forename: Jianying
authors.initials: J
authors.lastname: Ouyang
authors.forename: Yanguang
authors.initials: Y
authors.lastname: Zhang
authors.forename: Hsien-Tse
authors.initials: HT
authors.lastname: Tung
authors.forename: Shuqiong
authors.initials: S
authors.lastname: Lin
authors.forename: Robbert A L
authors.initials: RA
authors.lastname: Nagelkerke
authors.forename: David
authors.initials: D
authors.lastname: Kingston
authors.forename: Xiaohua
authors.initials: X
authors.lastname: Wu
authors.forename: Donald M
authors.initials: DM
authors.lastname: Leek
authors.forename: Diana
authors.initials: D
authors.lastname: Wilkinson
authors.forename: Chunsheng
authors.initials: C
authors.lastname: Li
authors.forename: In-Gann
authors.initials: IG
authors.lastname: Chen
authors.forename: Ye
authors.initials: Y
authors.lastname: Tao