Photoelectrochemical Polymerization for Solid-State Dye Sensitized Solar Cells

Dye sensitized solar cells represent promising alternative photovoltaic (PV) technologies with the advantages of low material cost, ease of production and high performance for indoor applications. Solid state DSCs (ssDSCs) have been developed to greatly diminish the problems of electrolyte leakage and electrode corrosion. However, the power conversion efficiency (PCEs) of ssDSCs generally was much lower than traditional liquid DSCs, resulting in low conductivity and poor pore infiltration of solid HTMs in mesoporous structures. To overcome these problems, in-situ photoelectrochemical polymerization (PEP) approach is developed to synthesize polymer HTMs in the porous electrodes, enabling enhancement of pore infiltration fraction and conductivity. The PEP method offers great opportunities for engineering the HTM interfaces, tuning the charge dynamics and improving the photovoltaic performance of ssDSCs. Here we aim to present a coherent review of the recent development of material engineering and interfacial optimization for ssDSCs. We also summarize the recent advances in the PEP, with special emphasis on how the influencing factors control the PEP kinetics, the polymer properties as well as the device performance. This review provides a deep understanding of the mechanism of photopolymerization across different conditions, which serves as a guidebook for further optimization of the PEP process for ssDSCs. This article is protected by copyright. All rights reserved.

Solid-state dye-sensitized solar cells using polymeric hole conductors

The present review presents the application of electronically conducting polymers (conducting polymers) as hole conductors in solid-state dye solar cells (S-DSSCs). At first, the basic principles of dye solar cell operation are presented. The next section deals with the principles of electrochemical polymerisation and its photoelectrochemical variety, the latter being an important, frequently-used technique for generating conducting polymers and hole conductors in DSSCs. Finally, two varieties of S-DSSC configurations, those of dry S-DSSC and of S-DSSCs incorporating a liquid electrolyte, are discussed.

Dye-sensitized solar cells strike back

Dye-sensitized solar cells (DSCs) are celebrating their 30th birthday and they are attracting a wealth of research efforts aimed at unleashing their full potential. In recent years, DSCs and dye-sensitized photoelectrochemical cells (DSPECs) have experienced a renaissance as the best technology for several niche applications that take advantage of DSCs' unique combination of properties: at low cost, they are composed of non-toxic materials, are colorful, transparent, and very efficient in low light conditions. This review summarizes the advancements in the field over the last decade, encompassing all aspects of the DSC technology: theoretical studies, characterization techniques, materials, applications as solar cells and as drivers for the synthesis of solar fuels, and commercialization efforts from various companies.

Molecular Engineering of D-π-A Type of Blue-Colored Dyes for Highly Efficient Solid-State Dye-Sensitized Solar Cells through Co-Sensitization

A novel blue-colored organic donor-π-acceptor sensitizer, the so-called MKA16 dye, has been employed to construct solid-state dye-sensitized solar cells (ssDSSCs). Using 2,2',7-,7'-tetrakis( N, N-di- p-methoxyphenyl-amine) 9,9'-spirobifuorene (Spiro-OMeTAD) as hole-transport material, a good conversion efficiency of 5.8% was recorded for cells based on the MKA16 dye and a high photovoltage of 840 mV in comparison with 5.6% efficiency using the known (Dyenamo Blue) dye. By co-sensitization using the orange-colored D35 dye and MKA16 together, the solid-state solar cells showed an excellent efficiency of 7.5%, with a high photocurrent of 12.41 mA cm^-2 and open-circuit voltage of 850 mV. The results show that the photocurrent of ssDSSCs can be significantly improved by co-sensitization mainly attributed to the wider light absorption range contributing to the photocurrent. In addition, results from photo-induced absorption spectroscopy show that the dye regeneration is efficient in co-sensitized solar cells. The current results possible routes of improving the design of aesthetic and highly efficient ssDSSCs.

Al2 O3 Underlayer Prepared by Atomic Layer Deposition for Efficient Perovskite Solar Cells

Perovskite solar cells, as an emergent technology for solar energy conversion, have attracted much attention in the solar cell community by demonstrating impressive enhancement in power conversion efficiencies. However, the high temperature and manually processed TiO₂ underlayer prepared by spray pyrolysis significantly limit the large-scale application and device reproducibility of perovskite solar cells. In this study, lowtemperature atomic layer deposition (ALD) is used to prepare a compact Al₂ O₃ underlayer for perovskite solar cells. The thickness of the Al₂ O₃ layer can be controlled well by adjusting the deposition cycles during the ALD process. An optimal Al₂ O₃ layer effectively blocks electron recombination at the perovskite/fluorine-doped tin oxide interface and sufficiently transports electrons through tunneling. Perovskite solar cells fabricated with an Al₂ O₃ layer demonstrated a highest efficiency of 16.2 % for the sample with 50 ALD cycles (ca. 5 nm), which is a significant improvement over underlayer-free PSCs, which have a maximum efficiency of 11.0 %. Detailed characterization confirms that the thickness of the Al₂ O₃ underlayer significantly influences the charge transfer resistance and electron recombination processes in the devices. Furthermore, this work shows the feasibility of using a high band-gap semiconductor such as Al₂ O₃ as the underlayer in perovskite solar cells and opens up pathways to use ALD Al₂ O₃ underlayers for flexible solar cells.

Novel and Stable D-A-π-A Dyes for Efficient Solid-State Dye-Sensitized Solar Cells

Two novel organic donor-acceptor-π-acceptor sensitizers, W7 and W8, have been applied in efficient solid-state dye-sensitized solar cells (ssDSSCs). Using 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenyl-amine) 9,9'-spirobifluorene (Spiro-OMeTAD) as hole-transport material (HTM), an excellent power conversion efficiency of 6.9% was recorded for W7, together with an excellent photocurrent of 10.51 mA cm^-2 and a high open-circuit voltage of 880 mV under standard AM 1.5 G illumination (100 mW cm^-2). The solid-state solar cells based on W8 showed an efficiency of 5.2%, with a good photocurrent of 9.55 mA cm^-2 and an open-circuit voltage of 870 mV. Compared to that of the well-known WS2 sensitizer, the results show that the performance of the ssDSSC devices can be significantly improved by introducing triphenylamine moiety into their structure. In addition, results of photoinduced absorption spectroscopy show efficient dye regeneration for W7- and W8-based devices. A higher hole conductivity of the W7/HTM and W8/HTM layers compared to that of the WS2/HTM layer was observed, indicating an efficient charge transfer at the interfaces. The results obtained offer insights into the design of reliable and highly efficient ssDSSCs for large-scale applications.

Matrix-assisted laser desorption/ionization mass spectrometric analysis of poly(3,4-ethylenedioxythiophene) in solid-state dye-sensitized solar cells: comparison of in situ photoelectrochemical polymerization in aqueous micellar and organic media

Solid-state dye-sensitized solar cells (sDSCs) are devoid of such issues as electrolyte evaporation or leakage and electrode corrosion, which are typical for traditional liquid electrolyte-based DSCs. Poly(3,4-ethylenedioxythiophene) (PEDOT) is one of the most popular and efficient p-type conducting polymers that are used in sDSCs as a solid-state hole-transporting material. The most convenient way to deposit this insoluble polymer into the dye-sensitized mesoporous working electrode is in situ photoelectrochemical polymerization. Apparently, the structure and the physicochemical properties of the generated conducting polymer, which determine the photovoltaic performance of the corresponding solar cell, can be significantly affected by the preparation conditions. Therefore, a simple and fast analytical method that can reveal information on polymer chain length, possible chemical modifications, and impurities is strongly required for the rapid development of efficient solar energy-converting devices. In this contribution, we applied matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) for the analysis of PEDOT directly on sDSCs. It was found that the PEDOT generated in aqueous micellar medium possesses relatively shorter polymeric chains than the PEDOT deposited from an organic medium. Furthermore, the micellar electrolyte promotes a transformation of one of the thiophene terminal units to thiophenone. The introduction of a carbonyl group into the PEDOT molecule impedes the growth of the polymer chain and reduces the conductivity of the final polymer film. Both the simplicity of sample preparation (only application of the organic matrix onto the solar cell is needed) and the rapidity of analysis hold the promise of making MALDI MS an essential tool for the physicochemical characterization of conducting polymer-based sDSCs.