Papers by Aravind Kumar Chandiran
Journal of Materials Chemistry A, 2022
Oxide ferroelectric materials based on ABO3 structure possess net electric polarization at zero a... more Oxide ferroelectric materials based on ABO3 structure possess net electric polarization at zero applied fields that give rise to new photovoltaic concepts. One of the peculiar properties which is specific...
Herein, we present the first use of a gallium oxide tunnelling layer to significantly reduce elec... more Herein, we present the first use of a gallium oxide tunnelling layer to significantly reduce electron recombination in dye-sensitized solar cells (DSC). The subnanometer coating is achieved using atomic layer deposition (ALD) and leading to a new DSC record open-circuit potential of 1.1 V with state-of-the-art organic D-π-A sensitizer and cobalt redox mediator. After ALD of only a few angstroms of Ga(2)O(3), the electron back reaction is reduced by more than an order of magnitude, while charge collection efficiency and fill factor are increased by 30% and 15%, respectively. The photogenerated exciton separation processes of electron injection into the TiO(2) conduction band and the hole injection into the electrolyte are characterized in detail.
Low temperature processing of Dye-sensitized Solar Cells (DSCs) is essential to enable commercial... more Low temperature processing of Dye-sensitized Solar Cells (DSCs) is essential to enable commercialization with low cost plastic substrates and diminish the overall manufacturing cost. We report a low temperature processing route for photoanodes where thin ZnO nanoshell is deposited by atomic layer deposition at 150 C, on a mesoporous insulating template. We found that a 6 nm ZnO overlayer on a 3 m mesoporous nanoparticle Al2O3 template shows a power conversion eeciency of 4.3% with the standard organic sensitizer (coded Y123) and cobalt bipyridine redox mediator.
Advanced Functional Materials, Oct 14, 2013
Electron recombination is one of the major loss factors in dye-sensitized solar cells (DSC), espe... more Electron recombination is one of the major loss factors in dye-sensitized solar cells (DSC), especially, with single electron outer sphere redox shuttle electrolyte. Insulating sub-nanometer oxide tunneling layers deposited by atomic layer deposition (ALD) are known to block the electron recombination, thereby leading to an increase in the open-circuit potential and the collection efficiency of the solar cell. A general perception in the DSC community is that any insulating oxide layer can block the recombination. However, in this work, it is unraveled that the insulating property of oxides alone is not sufficient. In addition, the properties such as the conduction band position and the oxidation state of the insulating oxide, the electronic structural modification induced to the underlying TiO2 mesoporous film, modification of surface charges (isoelectric point) and charge of the electrolyte species have to be considered. A complete photovoltaic study is done by depositing different cycles (by ALD) of four different insulating oxides (Ga2O3, ZrO2, Nb2O5, and Ta2O5) and their recombination characteristics, surface electronic properties, transport rate, and injection dynamics are investigated with a standard organic dye and Co2+/Co3+ redox mediator. A comparison is made with the conventional iodide/triiodide electrolyte.
ACS Applied Materials & Interfaces, Mar 18, 2013
Low-temperature processing of dye-sensitized solar cells (DSCs) is crucial to enable commercializ... more Low-temperature processing of dye-sensitized solar cells (DSCs) is crucial to enable commercialization with low-cost, plastic substrates. Prior studies have focused on mechanical compression of premade particles on plastic or glass substrates; however, this did not yield sufficient interconnections for good carrier transport. Furthermore, such compression can lead to more heterogeneous porosity. To circumvent these problems, we have developed a low-temperature processing route for photoanodes where crystalline TiO2 is deposited onto well-defined, mesoporous templates. The TiO2 is grown by atomic layer deposition (ALD), and the crystalline films are achieved at a growth temperature of 200 °C. The ALD TiO2 thickness was systematically studied in terms of charge transport and performance to lead to optimized photovoltaic performance. We found that a 15 nm TiO2 overlayer on an 8 μm thick SiO2 film leads to a high power conversion efficiency of 7.1% with the state-of-the-art zinc porphyrin sensitizer and cobalt bipyridine redox mediator.
Advanced Functional Materials, Jan 15, 2013
In this paper, a way of utilizing thin and conformal overlayer of titanium dioxide on an insulati... more In this paper, a way of utilizing thin and conformal overlayer of titanium dioxide on an insulating mesoporous template as a photoanode for dye-sensitized solar cells is presented. Different thicknesses of TiO2 ranging from 1 to 15 nm are deposited on the surface of the template by atomic layer deposition. This systematic study helps unraveling the minimum critical thickness of the TiO2 overlayer required to transport the photogenerated electrons efficiently. A merely 6-nm-thick TiO2 film on a 3-μm mesoporous insulating substrate is shown to transport 8 mA/cm2 of photocurrent density along with ≈900 mV of open-circuit potential when using our standard donor-π-acceptor sensitizer and Co(bipyridine) redox mediator.
Journal of the American Chemical Society, Oct 8, 2012
We report for the first time on a hole conductor-free mesoscopic methylammonium lead iodide (CH3N... more We report for the first time on a hole conductor-free mesoscopic methylammonium lead iodide (CH3NH3PbI3) perovskite/TiO2 heterojunction solar cell, produced by deposition of perovskite nanoparticles from a solution of CH3NH3I and PbI2 in γ-butyrolactone on a 400 nm thick film of TiO2 (anatase) nanosheets exposing (001) facets. A gold film was evaporated on top of the CH3NH3PbI3 as a back contact. Importantly, the CH3NH3PbI3 nanoparticles assume here simultaneously the roles of both light harvester and hole conductor, rendering superfluous the use of an additional hole transporting material. The simple mesoscopic CH3NH3PbI3/TiO2 heterojunction solar cell shows impressive photovoltaic performance, with short-circuit photocurrent Jsc= 16.1 mA/cm2, open-circuit photovoltage Voc = 0.631 V, and a fill factor FF = 0.57, corresponding to a light to electric power conversion efficiency (PCE) of 5.5% under standard AM 1.5 solar light of 1000 W/m2 intensity. At a lower light intensity of 100W/m2, a PCE of 7.3% was measured. The advent of such simple solution-processed mesoscopic heterojunction solar cells paves the way to realize low-cost, high-efficiency solar cells.
NanoLetters, Jun 11, 2012
Herein, we present the first use of a gallium oxide tunnelling layer to significantly reduce elec... more Herein, we present the first use of a gallium oxide tunnelling layer to significantly reduce electron recombination in dye-sensitized solar cells (DSC). The subnanometer coating is achieved using atomic layer deposition (ALD) and leading to a new DSC record open-circuit potential of 1.1 V with state-of-the-art organic D-π-A sensitizer and cobalt redox mediator. After ALD of only a few angstroms of Ga2O3, the electron back reaction is reduced by more than an order of magnitude, while charge collection efficiency and fill factor are increased by 30% and 15%, respectively. The photogenerated exciton separation processes of electron injection into the TiO2 conduction band and the hole injection into the electrolyte are characterized in detail.
Journal of the American Ceramic Society, Jun 15, 2012
Nanocrystalline anatase titanium dioxide powders were produced by a hydrothermal synthesis route ... more Nanocrystalline anatase titanium dioxide powders were produced by a hydrothermal synthesis route in pure form and substituted with trivalent Ga3+ and Y3+ or pentavalent Nb5+ with the intention of creating acceptor or donor states, respectively. The electrical conductivity of each powder was measured using the powder-solution-composite (PSC) method. The conductivity increased with the addition of Nb5+ from 3 × 10−3 S/cm to 10 × 10−3 S/cm in as-prepared powders, and from 0.3 × 10−3 S/cm to 0.9 × 10−3 S/cm in heat-treated powders (520°C, 1 h). In contrast, substitution with Ga3+ and Y3+ had no measureable effect on the material's conductivity. The lack of change with the addition of Ga3+ and Y3+, and relatively small increase upon Nb5+ addition is attributed to ionic compensation owing to the highly oxidizing nature of hydrothermal synthesis.
SCIENCE, Nov 4, 2011
The iodide/triiodide redox shuttle has limited the efficiencies accessible in dye-sensitized sola... more The iodide/triiodide redox shuttle has limited the efficiencies accessible in dye-sensitized solar cells. Here, we report mesoscopic solar cells that incorporate a Co(II/III)tris(bipyridyl)–based redox electrolyte in conjunction with a custom synthesized donor-π-bridge-acceptor zinc porphyrin dye as sensitizer (designated YD2-o-C8). The specific molecular design of YD2-o-C8 greatly retards the rate of interfacial back electron transfer from the conduction band of the nanocrystalline titanium dioxide film to the oxidized cobalt mediator, which enables attainment of strikingly high photovoltages approaching 1 volt. Because the YD2-o-C8 porphyrin harvests sunlight across the visible spectrum, large photocurrents are generated. Cosensitization of YD2-o-C8 with another organic dye further enhances the performance of the device, leading to a measured power conversion efficiency of 12.3% under simulated air mass 1.5 global sunlight.
The optoelectronic properties of transparent nanocrystalline TiO2 films were modified by the inco... more The optoelectronic properties of transparent nanocrystalline TiO2 films were modified by the incorporation of a low level of Ga3+ or Y3+ cations. After optimizing their relative concentration level, we were able to increase in a noticeable manner the power conversion efficiency from 7.4% to 8.1% for gallium and even to 9.0% in the case of yttrium where all three photovoltaic (PV) performance parameters were improved simultaneously. The beneficial effect of gallium and yttrium on the PV characteristics is attributed to a lower electrical resistance and longer electron lifetime enhancing the charge collection efficiency in the transparent layer. We also herein demonstrate that the substitution of the titanium site by a trivalent element in the benchmark TiO2 enables the disposal of the “magic” TiCl4(aq) post-treatment. The potential of this approach was also confirmed in solid-state PbS quantum-dot (QD) solar cells. In particular, a gallium-containing TiO2 anatase photoanode generated twice as much short-circuit photocurrent density as the standard electrode. A 1.9% power conversion efficiency has been achieved by using a solid-state heterojunction of the doped TiO2 with a 100 nm of PbS QD overlayer and using a gold back contact.
The optoelectronic properties of our benchmark nanocrystalline anatase TiO2 photoanode were modif... more The optoelectronic properties of our benchmark nanocrystalline anatase TiO2 photoanode were modified by means of aliovalent doping with Nb5+. Even for a low doping level, the charge collection efficiency can be noticeably improved as a result of a higher electron lifetime when using the heteroleptic Ru(+II) C101 dye. Particularly of interest, while this was only possible by adding additives in the electrolyte, the doping concentration allows tuning of the energetic of the trap state distribution; parameter particularly crucial for the injection rate and charge collection efficiency. This improvement brings the power conversion efficiency of a 7 μm thick transparent photoanode to 8.7% while intensifying the electrode’s transparency.
Applied Physics Letters, Nov 24, 2009
Polymer p-i-n homojunction light-emitting diodes (LEDs) comprising p-doped poly(dioctylfluorene-a... more Polymer p-i-n homojunction light-emitting diodes (LEDs) comprising p-doped poly(dioctylfluorene-alt-benzothiadiazole) (F8BT) hole-injection, intrinsic F8BT emitter, and n-doped F8BT electron-injection layers have been demonstrated. A thin F8BT film was photocrosslinked and bulk p-doped by nitronium oxidation, then overcoated with an F8BT layer which was then surface n-doped by contact printing with naphthalenide on an elastomeric stamp. These LEDs exhibit high built-in potential (Vbi = 2.2 V), efficient bipolar injection, and greatly improved external electroluminescence efficiency compared to control devices without the p-i-n structure. A modulated photocurrent technique was used to measure this Vbi, which systematically improves with diode structure.
Talks by Aravind Kumar Chandiran
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Papers by Aravind Kumar Chandiran
Talks by Aravind Kumar Chandiran