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C: Energy Conversion and Storage; Energy and Charge Transport
Solar Conversion Efficiency Performance of High Temperature Alloy over Low Temperature One: Comprehending Interfaces through Excitonics Study Tushar Debnath, Kausturi Parui, Sourav Maiti, and Hirendra N. Ghosh J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b03502 • Publication Date (Web): 08 May 2018 Downloaded from http://pubs.acs.org on May 8, 2018
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The Journal of Physical Chemistry
Solar Conversion Efficiency Performance of High Temperature Alloy over Low Temperature One: Comprehending Interfaces through Excitonics Study
Tushar Debnath†, Kausturi Parui†, Sourav Maiti†,$ and Hirendra N. Ghosh†,ǂ* Radiation & Photochemistry Division, Bhabha Atomic Research Centre, Mumbai – 400085, India.
†
ǂ
Institute of Nano Science and Technology, Mohali, Phase -10, Sector -64, Punjab 160062, India
$
Department of Chemistry, Savitribai Phule Pune University, Ganeshkhind, Pune 411007, India * E-mail:
[email protected],
[email protected] ACS Paragon Plus Environment
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Abstract: To take account of interface in the nanocrystal (NC) materials, we have synthesized high quantum yield gradient CdZnSSe alloy NC having minimal involvement of interface (G-300) through high temperature (300 ºC) pyrolysis and charge carrier dynamics was unraveled through femtosecond transient absorption studies. Gradient alloy of CdZnSSe (G-250) at low alloying temperature (250 ºC) was also synthesized where several interfaces were present in the form CdSe/CdS/ZnSe/ZnS within the alloy material along with other deep traps as well as surface defects. The successful formulation of minimal involvement of interface in G-300 alloy has been envisaged through its blue shifted optical absorption spectrum as compared to G-250 alloy due to interionic diffusion of less reactive Zn and S towards the core of the material at elevated reaction temperature that widen the band-gap. Unlike G-250 analogue no charge transfer (CT) state was observed in the G-300 alloy, which also suggests nonexistence of CdSe/CdS gradient type structure otherwise present for the G-250 analogue. The slow electron cooling time of 4 ps in the G-250 alloy found to be absent in G-300 alloy which can be attributed to minimal involvement of gradient structure otherwise where electron-hole decoupling leads to slower electron cooling. It has been observed that although the absorption cross-section of G-300 alloy is less in the solar spectrum as compared to G-250 analogue, photocurrent conversion efficiency (PCE) measurements of G-300 show promising 4.5% PCE due to smooth electron transfer to TiO2 through the interface free NCs whereas G-250 analogue shows only 3.5% PCE. Our investigation suggests that engineering with alloys having less gradient structure and without any boundary restrictions can lead us to new perceptions regarding the design and development of higher efficient quantum dot sensitized solar cell (QDSSC).
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The Journal of Physical Chemistry
Introduction The synthetic strategy of heteronanocrystal (HNC) developed in the last two decades can control several optoelectronic properties like size, shape and composition which can be efficiently applicable in photovoltaics, photocatalysis, nanoelectronics, bio-labeling, light emitting devices etc. 1-14 Since HNCs are formed by combination of two or more nanocrystals (NCs), the interface and strain between those NCs plays significant role in exciton dynamics as well as optoelectronic properties. 15-19 In addition that HNCs can offer either sharp or smooth interface; core-shell NCs offer sharp interface whereas smooth interface can be realized in alloy NCs.16,19-25 The carrier confinement potential varies abruptly from core to shell in core-shell NCs however in alloy NCs the smooth change in carrier confinement potential allows facile charge separation. The interfacial strain due to lattice mismatch also reduces significantly in alloy NCs removing interfacial defects which otherwise lowers the photoluminescence (PL) quantum yield (QY) of the NCs.17,23,26,27 It has been observed that depending on the reaction condition employed the alloy NCs can have gradient or homogeneous structure.19,28,29 At relatively low reaction temperature (
