• Energy Research

The growth of a TiO shell at the surface of TiO2 nanowires (NWs) allowed us to improve the power conversion efficiency of NW-based dye-sensitized solar cells (DSCs) by a factor 2.5. TiO2@TiO core-shell NWs were obtained by a two-step process: First, rutile-phase TiO2 NWs were hydrothermally grown. Second, a hongquiite-phase TiO shell was electrochemically deposited at the surface of the TiO2 NWs. Bare TiO2 and heterojunction TiO2@TiO NW-based DSCs were obtained using a cobalt(II/III) redox electrolyte and LEG4 as the dye. With this electrolyte/dye combination, DSCs with outstanding Voc values above 900 mV were systematically obtained. While TiO2@TiO NW-based DSCs had slightly lower Voc values than bare TiO2 NW-based DSCs, they provided 3-fold higher photocurrents, overall reaching 2.5-fold higher power conversion efficiencies. The higher photocurrents were associated with the larger surface roughness and an enhanced charge-carrier separation/transfer at the NW/dye interface.

The energy loss in dye-sensitized solar cells calculated from the energy difference between the lowest electronic transition of the dye and the obtained open-circuit voltage is often 1 eV or even more. To minimize this loss, it is important to accurately determine the energy alignment at the TiO(2)/dye/redox-mediator interface. In this study, we compared the results from electrochemistry and photoelectron spectroscopy for determining the energy alignment of three rylene dyes, two of which absorb relatively far in the red. The trends observed with the methods were different, as in the former, the energy alignment is measured relative to an external reference and includes contributions from solvent reorganization energies, while in the latter, it is measured relative to the energetics of the TiO(2) and is lacking such contributions. The influence of the dyes' dipole moments on the energetics of the TiO(2) was also measured and explained some of the differences in trends. Finally, we compared the injection efficiencies of the two red-absorbing dyes and found that the differences in injection efficiencies can be better explained using the energy alignment determined from photoelectron spectroscopy. This shows that the method for measuring the energetics of a DSC should be chosen according to what process one intends to study.

AbstractPerovskite has been adopted as photosensitizer to develop solid state p‐type mesoporous nickel oxide (NiO) dye‐sensitized solar cells (DSCs) employing PCBM as electron conductor. The optimal device achieved an efficiency of 1.5 % with an impressive open circuit voltage of more than 800 mV, which is the record of solar cell based on p‐type mesoporous NiO electrode. This result shows the potential for building highly efficient p‐type NiO solar cells as stand‐alone device.

AbstractLight‐soaking and high‐temperature storage testing of monolithic dye‐sensitised solar modules with total area module efficiencies above 5% have been performed. Our experiences from the development of a four‐layer monolithic dye‐sensitised solar test cell for comparative testing of material components for dye‐sensitised solar cells have directed our module development to a novel device design consisting of parallel‐connection of individual monolithic cells. The results from the accelerated testing of the modules (total area of 17.0 cm2) with four parallel‐connected cells (active area of 3.38 cm2/cell) are equivalent to those obtained for the monolithic single test cells when using identical device components. The successful transfer from cell to module stability is an important milestone in our ambition to develop a low‐cost Photovoltaic (PV) technology. Moreover, our results indicate that intensified research and development to define the procedures for relevant accelerated testing of dye‐sensitised solar modules is urgently required. Copyright © 2010 John Wiley & Sons, Ltd.

4- tert-Butylpyridine ( t-BP) is commonly used in solid state dye-sensitized solar cells (ssDSSCs) to increase the photovoltaic performance. In this report, the mechanism how t-BP functions as a favorable additive is investigated comprehensively. ssDSSCs were prepared with different concentrations of t-BP, and a clear increase in efficiency was observed up to a maximum concentration and for higher concentrations the efficiency thereafter decreases. The energy level alignment in the complete devices was measured using hard X-ray photoelectron spectroscopy (HAXPES). The results show that the energy levels of titanium dioxide are shifted further away from the energy levels of spiro-OMeTAD as the t-BP concentration is increased. This explains the higher photovoltage obtained in the devices with higher t-BP concentration. In addition, the electron lifetime was measured for the devices and the electron lifetime was increased when adding t-BP, which can be explained by the recombination blocking effect at the surface of TiO2. The results from the HAXPES measurements agree with those obtained from density functional theory calculations and give an understanding of the mechanism for the improvement, which is an important step for the future development of solar cells including t-BP.

Low‐temperature processed carbon‐based perovskite solar cells have received great attention due to low‐cost, high stability, and simple preparation processes that can be employed in large‐scale manufacturing. Carbon paste is deposited by techniques such as doctor blading or screen printing. However, solvents from this paste can damage the perovskite or underlying layers resulting in poor performance of solar cells. Furthermore, carbon is not an ideal hole‐selective contact. To overcome these issues, the antisolvent treatment is combined with the deposition of a polymeric hole conductor. Specifically, poly(3‐hexylthiophene) (P3HT), added into the chlorobenzene antisolvent, improves perovskite morphology and reduces interfacial carrier recombination. As a result, the power conversion efficiency (PCE) of solar cells with the device structure SnO2/MAPbI3/P3HT/carbon increases to 12.16% from 10.6% of pristine devices without P3HT, using pure antisolvent. For poly(triarylamine) hole conductor in the same method, PCE improves only slightly to 11.1%. After 260 h of thermal stress at 82 °C, the P3HT‐additive devices improve PCE up to 13.2% in air and maintain 91% of their initial efficiency over 800 h.

This paper describes the synthesis and characterization of core-shell structures, based on SnO2 and TiO2, for use in dye-sensitized solar cells (DSC). Atomic layer deposition is employed to control and vary the thickness of the TiO2 shell. Increasing the TiO2 shell thickness to 2 nm improved the device performance of liquid electrolyte-based DSC from 0.7% to 3.5%. The increase in efficiency originates from a higher open-circuit potential and a higher short-circuit current, as well as from an improvement in the electron lifetime. SnO2-TiO2 core-shell DSC devices retain their photovoltage in darkness for longer than 500 seconds, demonstrating that the electrons are contained in the core material. Finally core-shell structures were used for solid-state DSC applications using the hole transporting material 2,2',7,7',-tetrakis(N, N-di-p-methoxyphenyl-amine)-9,9',-spirofluorene. Similar improvements in device performance were obtained for solid-state DSC devices.

A new ruthenium complex, cis‐di(thiocyanato)(2,2′‐bipyridine‐4,4′‐dicarboxylic acid)(4,4′‐bis(2‐(5‐(2‐(4‐diphenylaminophenyl)ethenyl)‐thiophen‐2‐yl)ethenyl)‐2,2′‐bipyridine)ruthenium(II) (named E322) has been synthesized for use in dye‐sensitized solar cells (DSCs). Higher extinction coefficient and a broader absorption compared to the standard Ru‐dye, N719, were aimed. DSCs were fabricated with E322, and the efficiency was 0.12% initially. (4.06% for N719, as reference). The efficiency was enhanced to 1.83% by exposing the cell under simulated sunlight containing UV‐irradiation at short‐circuit condition. The reasons of this enhancement are (1) enhanceing electron injection from sensitizer to TiO2 following a shift toward positive potentials of the conduction band of TiO2 by the adsorption of protons or cations from the sensitizer, or from the redox electrolyte and (2) improving the regeneration reaction of the oxidized dye by the redox electrolyte by the dissolution of aggregated dye from the surface of TiO2 following the treatment.