Indium tin oxide as a semiconductor material in efficient p-type dye-sensitized solar cells

Abstract

Indium tin oxide (ITO) is a well-known n-type degenerate semiconductor with a wide variety of electronic and optoelectronic applications. Herein ITO is utilized as a photocathode material in p-type dye-sensitized solar cells in place of the commonly applied and highly colored nickel oxide (NiO) semiconductor. The application of mesoporous ITO photocathodes, [Fe(acac) 3 ] 0/ − as a redox mediator and a new organic dye afforded an impressive energy conversion efficiency of 1.96 ± 0.12%. Comparative transient absorption spectroscopic studies indicated that the recombination rate at the ITO-electrolyte interface is two orders of magnitude faster than that of NiO. Analysis of the operation mechanism of the ITO-based devices with ultraviolet photon spectroscopy and photoelectron spectroscopy in air showed that ITO exhibits a significant local density of states arising below − 4.8 eV, which enables electron transfer to occur from the ITO to the excited dye, thus giving rise to the sustained photocathodic current. NPG Asia Materials (2016) 8, e305; doi:10.1038/am.2016.89; published online 9 September 2016 INTRODUCTION Transparent conducting oxides have been extensively used in optoelectronic applications. 1-3 One common transparent conducting oxide is indium tin oxide (ITO). ITO is a well-known n-type degenerate semiconductor 4 with an optical band gap of 3.5-4.3 eV 5 and has a high transmission in the near infrared and visible regions of the electromagnetic spectrum. Owing to their high optical transparency, good electrical conductivity, chemical inertness, hardness and excellent substrate adherence, 6-8 ITO thin films are applied in flat panel displays, antistatic coatings, solar cells, camera lenses and architectural glazing. 9-12 Additionally, high-surface-area mesoporous ITO films have been used as sensors for gases, such as ammonia, nitric oxide, ethanol and methanol. [13][14][15][16] Moreover, ITO films and ITO/TiO 2 core-shell structures have been utilized as photoanodes in both dye-sensitized solar cells (DSCs) and water oxidation devices. [17][18][19][20] A recent spectroscopic investigation into the charge transfer dynamics of dye-coated ITO films revealed that ITO can both accept and donate electrons during photoinduced charge transfer. 21,22 By exploiting the ambivalent property of this degenerate n-type semiconductor, we have developed an efficient p-type DSC (p-DSC)

Sonication‐Assisted Synthesis of Gallium Oxide Suspensions Featuring Trap State Absorption: Test of Photochemistry

“…PESA analysis is usually conducted to determine work function of metals and the ionization potential (IP) of semiconductors. The IP of semiconductors may refer to either the valence band position or to trap states within the bandgap, provided that their density is high enough to result in a detectable signal . The PESA spectrum of Ga 2 O 3 (Figure c) reveals an unusual two‐step dependency instead of the commonly observed single emission edge.…”

“…The observations are similar to reports on tin‐doped indium oxide, where the measured IP corresponds to the top of the dopant‐associated trap band and the PESA signal corresponds to the Fermi level of the material. [23a]…”

Introducing Molecular Functionalities within High Surface Area Nanostructured ITO Electrodes through Diazonium Electrografting

“…Among the available wide band‐gap metal oxides, tin‐doped indium oxide (ITO) has the great advantage of combining high electrical conductivity with good transparency in the visible. Moreover, as degenerate n ‐type semiconductors, nanostructured films of ITO can be used either as photoanodes or photocathodes, depending on the type of dye‐sensitizer and light excitation …”

“…Moreover, as degenerate n-type semiconductors, [1] nanostructured films of ITO can be used either as photoanodes or photocathodes, depending on the type of dye-sensitizer and light excitation. [2][3][4][5][6] One of the crucial issues for efficient and stable dyesensitized photoelectrodes is the degree of electronic coupling and stability with which the molecular sensitizer is chemically anchored onto the metal oxide surface. Indeed, it has to be strong enough to withstand the hydrolytic conditions generally required for sustainable and eco-friendly devices, [7] and, at the same time, it must lead to an efficient electronic coupling between the dye and the metal oxide to allow fast interfacial electron transfer reactions.The most commonly used method for dye sensitization of metal oxide surfaces is by chemisorption of carboxylate or phosphonate anchoring groups present on the dye molecule.…”

Recent Advances in Optimization of Photoanodes and Counter Electrodes of Dye-Sensitized Solar Cells

“…After photoexcitation of the sensitizer, in n-type DSSCs an electron is injected into the conduction band of the semiconductor, whereas in the p-type DSSCs a hole is injected in the valence band of the semiconductor. Efforts have been made towards fabricating purely p-type DSSCs, such as the manufacture of indium tin oxide (ITO) photoanodes by Yu et al 13 . Despite making use of [Fe(acac) 3 ] 0/-solution as the redox electrolyte, a PCE value of only about 1.96% (0.12%) was reported.…”