CdS/CdSe-sensitized nanostructured SnO(2) solar cells exhibiting record short-circuit photocurrent densities have been fabricated. Under simulated AM 1.5, 100 mW cm(-2) illumination, photocurrents of up to 17.40 mA cm(-2) are obtained, some 32% higher than that achieved by otherwise identical semiconductor-sensitized solar cells (SSCs) employing nanostructured TiO(2). An overall power conversion efficiency of 3.68% has been achieved for the SnO(2)-based SSCs, which compares very favorably to efficiencies obtained by the TiO(2)-based SSCs. The characteristics of these SSCs were studied in more detail by optical measurements, spectral incident photon-to-current efficiency (IPCE) measurements, and impedance spectroscopy (IS). The apparent conductivity of sensitized SnO(2) photoanodes is apparently too large to be measured by IS, yet for otherwise identical TiO(2) electrodes, clear electron transport features could be observed in impedance spectra, tacitly implying slower charge transport in TiO(2). Despite this, electron diffusion length measurements suggest that charge collection losses are negligible in both kinds of cell. SnO(2)-based SSCs exhibit higher IPCEs compared with TiO(2)-based SSCs which, considering the similar light harvesting efficiencies and the long electron diffusion lengths implied by IS, is likely to be due to a superior charge separation yield. The resistance to charge recombination is also larger in SnO(2)-based SSCs at any given photovoltage, and open-circuit photovoltages under simulated AM 1.5, 100 mW cm(-2) illumination are only 26-56 mV lower than those obtained for TiO(2)-based SSCs, despite the conduction band minimum of SnO(2) being hundreds of millielectronvolts lower than that of TiO(2).

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Kesterite Cu2ZnSnS4 (CZTS) photovoltaics have been comprehensively investigated in the past decades but are still hampered by a relatively large open circuit voltage (V oc) deficit, which is correlated to bulk defects in CZTS and interface recombination. Heterojunction interface management is of critical importance to tackle the interface recombination. In this work, we use atomic layer deposition (ALD) to synthesize a wide range of Zn1–x Sn x O (ZTO, 0 ≤ x ≤ 1) films for application as a buffer layer in CZTS solar cells. A favorable band alignment is achieved using a 10 nm Zn0.77Sn0.23O buffer layer that enabled an impressive 10% increase in open circuit voltage of the CZTS solar cell. The microstructure and chemical nature of the CZTS/ZTO interface are carefully studied and the presence of an ultrathin Zn­(S, O) tunnel layer is demonstrated. The decreased interfacial defects stemming from the minor lattice mismatch at the CZTS/Zn­(S,O)/ZTO heterointerface in combination with the passivation provided by a higher sodium concentration throughout the CZTS/ZTO device explains the significant increase in open circuit voltage. Finally, we demonstrate a CZTS solar cell efficiency of 9.3%, which is the highest efficiency for Cd-free pure sulfide CZTS solar cell to date to the best of our knowledge.

Mesoporous SnO2 spheres of tunable particle size were synthesized for the first time by facile electrochemical anodization of tin foil in alkaline media. As the anodization process involves no sophisticated reactor or toxic chemicals, and proceeds continuously under ambient conditions, it provides an economic way of synthesizing nanostructured SnO2 on a large scale. Structural characterization indicates that these spherical particles consist of an agglomeration of SnO2 nanocrystals, resulting in a high internal surface area. This makes them a promising photoanode material for use in semiconductor-sensitized solar cells (SSCs). By using the successive ionic-layer adsorption and reaction method, a thin layer of CdSe was conformally coated on the surface of SnO2 nanocrystals, which were previously treated with aqueous TiCl4 solution. Efficient charge separation was observed by photoluminescence spectroscopy. After deposition of a ZnS passivation layer onto the CdSe light-harvesting layer, a power conversion efficiency of ∼1.91% was achieved in a regenerative photoelectrochemical cell. Factors dictating interfacial charge recombination and charge separation are discussed and compared to those in its molecular dye-sensitized counterpart. This study represents the first attempt so far of using mesoscopic SnO2 as a photoanode in a SSC device, and characterizing it under simulated AM 1.5, 100 mW cm−2 illumination. The results are a step toward development of highly efficient SSCs employing novel electron transport materials and sensitizers, such as infrared light absorbers PbS, CuInSe2, etc.

An aqueous spray-pyrolysis approach for synthesizing Cu(In,Ga)(S,Se)2 thin film, which leads to 10.54% power conversion efficiency in solar cell, and shows ease of fabrication of films in large-scale at a much cheaper cost.

Compact nickel oxide (NiO) thin films were prepared on various substrates via a simple spray pyrolysis technique. Morphological and structural characterization indicates that these NiO films are very uniform in thickness (100 nm) and possess the bunsenite crystal structure. Optical measurements show that the NiO films are highly transparent with a band gap of 3.706 0.05 eV. Mott-Schottky plots obtained from electrochemical impedance spectroscopy measurements reveal that the as-deposited NiO on fluorine-doped tin oxide (FTO) glass behaves as a p-type semiconductor. The flat band potential of NiO was estimated to be 0.36 V (vs. NHE) in 0.10 M tetrabutylammonium perchlorate/acetonitrile electrolytes. Cyclic voltammetric measurements of the NiO films on FTO in various redox electrolytes show that electrochemical reactions proceed in the accumulation region but are com-pletely inhibited in the depletion region, indicating the NiO films effectively block the FTO substrate. Using these NiO blocking layers, a CdS-sensitized mesoscopic NiO photocathode operating in a polysulfide electrolyte is unambiguously demonstrated for the first time. It is anticipated that NiO thin films synthesized by spray pyrolysis could find important applications as stable and transparent electron barrier layers for various optoelectronic devices. VC 2011 The Electrochemical Society. [DOI: 10.1149/1.3590742] All rights reserved. Manuscript submitted January 25, 2011; revised manuscript received April 5, 2011. Published May 18, 2011. Nickel oxide (NiO) is a wide band-gap (Eg> 3.60 eV) semicon-ductor, which naturally possesses p-type conductivity and is one o

Metal oxide semiconductors with lower lying conduction band minimum and superior electron mobility are essential for efficient charge separation and collection in PbS-sensitized solar cells. In the present study, mesoscopic SnO(2) was investigated as an alternative photoanode to the commonly used TiO(2) and examined comprehensively in PbS-sensitized liquid junction solar cells. To exploit the capability of PbS in an optimized structure, cascaded nPbS/nCdS and alternate n(PbS/CdS) layers deposited by a successive ionic layer adsorption and reaction method were systematically scrutinized. It was observed that the surface of SnO(2) has greater affinity to the growth of PbS compared with TiO(2), giving rise to much enhanced light absorption. In addition, the deposition of a CdS buffer layer and a ZnS passivation layer before and after a PbS layer was found to be beneficial for efficient charge separation. Under optimized conditions, cascaded PbS/CdS-sensitized SnO(2) exhibited an unprecedented photocurrent density of 17.38 mA cm(-2) with pronounced infrared light harvesting extending beyond 1100 nm, and a power conversion efficiency of 2.23% under AM 1.5, 1 sun illumination. In comparison, TiO(2) cells fabricated under similar conditions showed much inferior performance owing to the less efficient light harnessing of long wavelength photons. We anticipate that the systematic study of PbS-sensitized solar cells utilizing different metal oxide semiconductors as electron transporters would provide useful insights and promote the development of semiconductor-sensitized mesoscopic solar cells employing panchromatic sensitizers.

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