Article pubs.acs.org/JPCC
Multiple Charge Transfer Dynamics in Colloidal CsPbBr3 Perovskite Quantum Dots Sensitized Molecular Adsorbate Partha Maity, Jayanta Dana, and Hirendra N. Ghosh* Radiation and Photochemistry Division, Bhabha Atomic Research Centre, Mumbai, 400085, India S Supporting Information *
ABSTRACT: Ultrafast charge-transfer (CT) dynamics has been verified in CsPbBr3 (CPB) quantum dot (QD)−4,5-dibromofluorescein (DBF) composite materials, which form a strong CT complex in the ground state and can absorb more photons in the red region of the solar spectrum. Cyclic voltammetry and steady state luminescence studies suggest that the conduction (CB) and valence bands (VB) of CPB lie, respectively, below the LUMO and the HOMO of the DBF molecule. Steady state and time-resolved luminescence measurements with selective photoexcitation reveal the photoexcited hole transfer from CPB QDs to the DBF molecule, which is thermodynamically viable. Additionally, a redshifted PL band was detected upon excitation of the CT complex that has been attributed to CT luminescence. Femtosecond transient absorption measurements have been performed to measure the hole transfer and direct electron transfer processes in the composite system and have been measured to be 1−1.25 ps and 20% photocurrent conversion efficiency, the thermal stability of these solar cell is a matter of major concern. To improve the thermal stability, a new class of completely inorganic-based cesium lead trihalide perovskite material has been incorporated in the perovskite solar cell by Kulbak et al.,8 which shows a stable ∼6.6% solar efficiency. The bright and novel optoelectric properties with the wide color gamut of these cesium lead trihalide (CsPbX3: X = Cl, Br, I) based colloidal perovskite QDs was first reported by Kovalenko et al.9 In addition to the thermal stability, the synthesized lead-based metal halide perovskite colloidal QDs (CsPbX3) are found to have higher order absorption cross-section, narrow photoluminescence (PL) bandwidth, tunable PL behavior, and high emission quantum yield (∼90%).9−14 With these exciting properties, the lead-based cesium trihalide semiconductor NCs have also been concomitantly started in research for several applications such as light-emitting diodes, photovoltaic, bioimaging, lasers, and so on.10,15−21 © 2016 American Chemical Society
Received: July 8, 2016 Revised: July 24, 2016 Published: July 25, 2016 18348
DOI: 10.1021/acs.jpcc.6b06853 J. Phys. Chem. C 2016, 120, 18348−18354
Article
The Journal of Physical Chemistry C
and Horiba Canada model no. PTI QM-400 spectrofluorimeter, respectively. 2.3. Time-Resolved Emission Spectrometer. Timecorrelated single photon counting (TCSPC) measurements has been used to carry out time-resolved fluorescence measurements which is a diode laser based spectrofluorimeter from IBH (U.K). In the present work 445 nm laser pulses were used as the excitation light sources and a TBX4 detection module (IBH) coupled with a special Hamamatsu PMT was used for fluorescence detection. 2.4. Ultrafast Transient Absorption (TA) Studies. Details experimental setup of the TA measurement has been reported in our previous report.37 In brief, femtosecond transient absorption measurements were carried out at 400 nm laser excitation and probe at UV, visible to near IR region. Excited state dynamics are measured from 0.1 ps to 4 ns time scale using Excipro spectrometer (CDP, Moscow). The seed pulses of 800 nm, 50 fs pulse duration, 100 MHz repetition rate, and ∼4 nJ/pulse energy is generated from a self-modelocked Ti:sapphire laser oscillator (Tissa 50, CDP, Moscow, Russia). The pulses are amplified in a multipass amplifier pumped by a 20W diode pump solid state (DPSS) laser (JadeII, Thales Laser, France) to generate
