Hi-jung Kim

High-Performance Nanostructured Inorganic−Organic Heterojunction Solar Cells

We report all solid-state nanostructured inorganic-organic heterojunction solar cells fabricated by depositing Sb(2)S(3) and poly(3-hexylthiophene) (P3HT) on the surface of a mesoporous TiO(2) layer, where Sb(2)S(3) acts as an absorbing semiconductor and P3HT acts as both a hole conductor and light absorber. These inorganic-organic light harvesters perform remarkably well with a maximum incident-photon-to-current efficiency (IPCE) of 80% and power conversion efficiency of 5.13% under air-mass 1.5 global (AM 1.5G) illumination with the intensity of 100 mW cm(-2). These devices are highly stable under room light in air, even without encapsulation. The present findings offer novel directions for achieving high-efficiency solid-state solar cells by hybridization of inorganic-organic light harvesters and hole transporters.

All solid state multiply layered PbS colloidal quantum-dot-sensitized photovoltaic cells

The combination of solution processable colloidal quantum dots (CQDs) and organic conjugated polymers has attracted growing interest in the past few years, because devices fabricated using this combination can have potentially low cost and high efficiency. In this paper, we propose a new device architecture of multiply layered PbS CQD-sensitized photovoltaic cells. The multiple layers of PbS CQDs were formed by the repeated spin-coating of oleic-acid-capped PbS CQD solution and 1 wt% 1,2-ethanedithiol (EDT) solution onto mesoporous (mp)-TiO2 as photoanode. Through the structural advantage of a sensitized type device and post-treatment in 10 wt% EDT solution for 16 h, we could fabricate efficient photovoltaic cells having an overall energy conversion efficiency of 2.9% under 1 sun illumination, and an external quantum efficiency of over 15% at zero bias with a signal attenuation to frequency of 10 kHz levels in the near-infrared (NIR) range.

Performance improvement of Sb2S3-sensitized solar cell by introducing hole buffer layer in cobalt complex electrolyte

We found that the insertion of the poly-3-hexylthiophene (P3HT) layer into the pristine device results in great improvement of the efficiency, from 2.0% to 3.3% at 1 sun illumination. The improvement was mainly attributed to the improved fill factor, which for the Sb2S3 sensitized solar cell was seriously degraded from 56.0% (at 0.1 sun) to 31.5% (at 1 sun), whereas the fill factor of the Sb2S3/P3HT sensitized solar cell was only moderately degraded, from 59.3% (at 0.1 sun) to 40.4%. The role of P3HT as a hole buffer layer was analyzed by electrochemical impedance spectroscopy (EIS).

Hole-conducting mediator for stable Sb2S3-sensitized photoelectrochemical solar cells

Iodide redox (3I−/I3−), polysulfide redox (S2−/Sx2−), organic redox [TMTU/TMFDS2+: tetramethylthiourea/tetramethylformaminium-bis(trifluoromethanesulfonyl)imide], ferrocene redox (Fc/Fc+), nickel redox [Ni(II)/Ni(III)], and cobalt redox [Co(II)/Co(III)] hole conducting electrolytes were systematically investigated to determine their suitability for use in Sb2S3-sensitized photoelectrochemical solar cells. A long-term stability test and UV-visible spectral analyses revealed that Sb2S3-sensitized photoelectrochemical solar cells worked stably with Co(II)(o-phen)3(TFSI)2/Co(III)(o-phen)3(TFSI)3 [TFSI: bis(trifluoromethanesulfonyl)imide] as the redox mediator.

Near-infrared responsive PbS-sensitized photovoltaic photodetectors fabricated by the spin-assisted successive ionic layer adsorption and reaction method

A PbS-sensitized photovoltaic photodetector responsive to near-infrared (NIR) light was fabricated by depositing monolayered PbS nanoparticles on a mesoporous TiO(2) (mp-TiO(2)) film via the spin-assisted successive ionic layer adsorption and reaction (SILAR) method. By adjusting the size and morphology of the PbS nanoparticles through repeated spin-assisted SILAR cycles, the PbS-sensitized photovoltaic photodetector achieved an external quantum efficiency of 9.3% at 1140 nm wavelength and could process signals up to 1 kHz.

Origin of Nonlinear Device Performance with Illuminated Sun Intensity in Mesoscopic Sb2S3-sensitized Photoelectrochemical Solar Cells using Cobalt Electrolyte

ABSTRACT: The mesoscopic Sb 2 S 3 -sensitized photoelectrochemical solar cells using cobalt redox electrolyteexhibit nonlinear behavior of power conversion efficiency with illuminated sun intensity. From themeasurement of bulk diffusion and electrochemical impedance spectroscopy studies, we suggestthat the nonlinearity of device performance with illuminated sun intensity is attributed not to theslow bulk diffusion problem of cobalt electrolyte but to the limited mass transport in narrowed porevolume in mesoscopic TiO 2 electrode.Keywords : Sb 2 S 3 , Photoelectrochemical solar cell, TiO 2 , Cobalt electrolyte Received September 15, 2011: Accepted September 29, 2011 1. Introduction Since Gratzel et al. 1) reported a mesoscopic dye-sensitized photoelectrochemical solar cell with highpower conversion efficiency over 11% at 1 sun illumination,the sensitized photoelectrochemical solar cells have beenintensively studied due to their distinguished device structurefrom conventional p-n heterojunction solar cells. The sensi-tized solar cells are comprised to mesoscopic photoanode,sensitizer, and redox electrolyte which has correspondingrole of electron conductor, light absorber, and hole con-ductor, respectively. This unique device architecture enablesthe sensitized solar cells to hold cost-effectiveness.Recently inorganic semiconductors have been con-sidered as a promising alternative of conventional dyesbecause of their peculiar properties such as easy chargeseparation by higher dipole moment, ~10 fold higherextinction coefficient than Ru/organic dyes, convenientbandgap tunability by size control, and multiple excitongeneration.