Fantai Kong

Review of Recent Progress in Dye-Sensitized Solar Cells

We introduced the structure and the principle of dye-sensitized solar cell (DSC). The latest results about the critical technology and the industrialization research on dye-sensitized solar cells were reviewed. The development of key components, including nanoporous semiconductor films, dye sensitizers, redox electrolyte, counter electrode, and conducting substrate in dye-sensitized solar cells was reviewed in detail. The developing progress and prospect of dye-sensitized solar cells from small cells in the laboratory to industrialization large-scale production were reviewed. At last, the future development of DSC was prospective for the tendency of dye-sensitized solar cells.

Low molecular mass organogelator based gel electrolyte with effective charge transport property for long-term stable quasi-solid-state dye-sensitized solar cells.

Stable quasi-solid-state dye-sensitized solar cells (DSC) were fabricated using 12-hydroxystearic acid as a low molecular mass organogelator (LMOG) to form gel electrolyte. TEM image of the gel exhibited the self-assembled network constructed by the LMOG, which hindered flow and volatilization of the liquid. The formation of less-mobile polyiodide ions such as I 3 (-) and I 5 (-) confirmed by Raman spectroscopy increased the conductivity of the gel electrolytes by electronic conduction process, which should be rationalized by the Grotthuss-type electron exchange mechanism caused by rather packed polyiodide species in the electrolytes. The results of the accelerated aging tests showed that the gel electrolyte based dye-sensitized solar cell could retain over 97% of its initial photoelectric conversion efficiency value after successive heating at 60 degrees C for 1000 h and device degradation was also negligible after one sun light soaking with UV cutoff filter for 1000 h.

Superior Light-Harvesting Heteroleptic Ruthenium(II) Complexes with Electron-Donating Antennas for High Performance Dye-Sensitized Solar Cells

Three heteroleptic polypyridyl ruthenium complexes, RC-41, RC-42, and RC-43, with efficient electron-donating antennas in the ancillary ligands were designed, synthesized, and characterized as sensitizers for dye-sensitized solar cell. All the RC dye sensitizers showed remarkable light-harvesting capacity and broadened absorption range. Significantly, RC-43 obtained the lower energy metal-ligand charge transfer (MLCT) band peaked at 557 nm with a high molar extinction coefficient of 27 400 M(-1) cm(-1). In conjunction with TiO2 photoanode of submicrospheres and iodide-based electrolytes, the DSSCs sensitizing with the RC sensitizers, achieved impressively high short-circuit current density (19.04 mA cm(-2) for RC-41, 19.83 mA cm(-2) for RC-42, and 20.21 mA cm(-2) for RC-43) and power conversion efficiency (10.07% for RC-41, 10.52% for RC-42, and 10.78% for RC-43). The superior performances of RC dye sensitizers were attributed to the enhanced light-harvesting capacity and incident-photon-to-current efficiency (IPCE) caused by the introduction of electron-donating antennas in the ancillary ligands. The interfacial charge recombination/regeneration kinetics and electron lifetime were further evaluated by the electrochemical impedance spectroscopy (EIS) and transient absorption spectroscopy (TAS). These data decisively revealed the dependences on the photovoltaic performance of ruthenium sensitizers incorporating electron-donating antennas.

Tetraphenylmethane-Arylamine Hole-Transporting Materials for Perovskite Solar Cells

A new class of hole-transporting materials (HTM) containing tetraphenylmethane (TPM) core have been developed. After thermal, charge carrier mobility, and contact angle tests, it was found that TPA-TPM (TPA: arylamine derivates side group) showed higher glass-transition temperature and larger water-contact angle than spiro-OMeTAD with comparable hole mobility. Photoluminescence and impedance spectroscopy studies indicate that TPA-TPMs hole-extraction ability is comparable to that of spiro-OMeTAD. SEM and AFM results suggest that TPA-TPM has a smooth surface. When TPA-TPM is used in mesoscopic perovskite solar cells, power conversion efficiency comparable to that of spiro-OMeTAD is achieved. Notably, the perovskite solar cells employing TPA-TPM show better long-term stability than that of spiro-OMeTAD. Moreover, TPA-TPM can be prepared from relatively inexpensive raw materials with a facile synthetic route. The results demonstrate that TPM-arylamines are a new class of HTMs for efficient and stable perovskite solar cells.

Diketopyrrolopyrrole or benzodithiophene-arylamine small-molecule hole transporting materials for stable perovskite solar cells

Two simple small-molecular arylamine derivatives 4-methoxy-N-(4-methoxyphenyl)-N-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)aniline (OMeTPA-DPP) and 4,4′-(4,8-bis((2-ethylhexyl)oxy)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl)bis(N,N-bis(4-methoxyphenyl)aniline) (OMeTPA-BDT) linked with diketopyrrolopyrrole or benzodithiophene moieties have been synthesized. The new compounds show better thermal stability than spiro-OMeTAD. The steady-state and time-resolved photoluminescence demonstrate that the new compounds have good hole extraction ability. The perovskite solar cells employing OMeTPA-BDT show a comparable power conversion efficiency with that of spiro-OMeTAD. After more than 200 hours of aging under one sun illumination, the residual efficiencies of the PSCs based on OMeTPA-DPP, OMeTPA-BDT and spiro-OMeTAD are 8.69%, 11.15% and 9.08%, respectively. The results demonstrate that the newly-developed compounds can act as efficient hole transporting materials for stable perovskite solar cells.

Broad spectral-response organic D–A–π–A sensitizer with pyridine-diketopyrrolopyrrole unit for dye-sensitized solar cells

In this work, four D–A–π–A sensitizers PDPP-I–IV based on pyridine-flanked DPP moieties (PDPP) were designed and synthesized for dye-sensitized solar cells. Remarkably, the incorporated electron-withdrawing unit of pyridine-flanked DPP improves the light-harvesting ability and modifies the electrochemical and absorption properties, generating a broader IPCE wavelength responding region. The electrochemical experiments and time-resolved photoluminescence measurements indicate the ability of electron-injection into the TiO2 conductive band from the excited sensitizer. The transient absorption spectra were measured to investigate the feasibility of the dynamics for oxidized-state sensitizer regeneration. The IPCE spectra demonstrate the broad spectral response region of these sensitizers. Especially, the IPCE of PDPP-III reached the near infrared (NIR) region (>800 nm) with the highest short-circuit current of 16.17 mA cm−2 in these sensitizers. Furthermore, the electrochemical impedance spectroscopy (EIS) experiments suggest that the electron-lifetime and charge recombination resistance increased when attaching the stereo substituted groups (R2) on the PDPP moiety, resulting in a higher open-circuit voltage (Voc). It can be found that PDPP-II based DSSCs with liquid electrolyte exhibited the highest Voc (523 mV) and power conversion efficiency (PCE) of 5.26%.

Molecular Engineering of Simple Benzene–Arylamine Hole-Transporting Materials for Perovskite Solar Cells

Three benzene-arylamine hole-transporting materials (HTMs) with different numbers of terminal groups were prepared. It is noted that the molecule with three arms (H-Tri) shows a lower highest occupied molecular orbital level and a better film morphology on perovskite layer than the molecules with two or four arms (H-Di, H-Tetra). When these molecules were applied to the perovskite solar cells, the H-Tri-based one showed better performance compared with the H-Di- or H-Tetra-based ones. Photoluminescence and impedance spectroscopy demonstrate that H-Tri can improve the hole-electron separation efficiency and decrease the charge recombination, thus leading to a better performance. Moreover, the H-Tri-based device shows a comparable performance and a much less materials cost than the conventional spiro-OMeTAD. Therefore, we have presented a new low-cost and high-performance HTM through simple molecular engineering.

Influence of Structure and Morphology of Perovskite Films on the Performance of Perovskite Solar Cells

Perovskite solar cells based on the inorganic/organic hybrid perovskite have attracted increasing attention over the past 3 years. Many studies have been done in this area. Controling the morphology of the perovskite film is an effective way to improve the photoelectric conversion efficiency of the devices. In our reserch, we studied the influence of structure and morphology of perovskite films on the performance of the organic-inorganic hybrid perovskite solar cells which prepared by a sequential deposition method. Mesoporous TiO2 scaffold were introduced as electron collecting layer. Lead iodide (PbI2) was then spin cast on the TiO2 scaffold. The PbI2 subsequently transformed into the perovskite (CH3NH3PbI3) by dipping the TiO2/PbI2 film into a solution of CH3NH3I. We studied the difference between the PbI2 film with or without drying under room temperature after spin-coating. Through drying under room temperature, larger pores formed in the PbI2 film. While without drying under room temperature, smaller and shallower pores formed in the PbI2 film. The results show that larger pores in PbI2 film leads to more complete transformation of PbI2 to CH3NH3PbI3 and larger CH3NH3PbI3 particles. CH3NH3PbI3 films were prepared with three different processes: (a) direct dipping the PbI2 film with smaller pores into the CH3NH3I solution; (b) direct dipping the PbI2 with larger pores into the CH3NH3I solution; (c) dipping the PbI2 with larger pores into the CH3NH3I solution after pre-wetting.The resulting CH3NH3PbI3 films were studied with SEM, UV-vis absorption spectrum and XRD. The particles size of the CH3NH3PbI3 are 150, 250 and 350 nm for process (a), (b) and (c) respectively. CH3NH3PbI3 films fabricated through process (a) show insufficient absorption due to the insufficient transformation of the PbI2. The pre-wetting procedure leads to slower reaction result in larger CH3NH3PbI3 particle size. Devices with proper size of CH3NH3PbI3 particles show the highest photoelectric conversion efficiency. An efficiency of 13.5% was achieved with a Jsc of 17.8 mA/cm, a Voc of 1.05 V and a FF of 72.5%.

Ruthenium complexes as sensitizers with phenyl-based bipyridine anchoring ligands for efficient dye-sensitized solar cells

Two ruthenium complex dye sensitizers, Ru(NCS)2 LL′, in which L refers to 4,4′-dinonyl-2,2′-bipyridine and L′ stands for 4,4′-di(m-X-benzoic acid)-2,2′-bipyridine (X = H (RC-73), F (RC-76)), were designed and synthesized to investigate the influence of introducing phenyl-based bipyridine anchoring ligands and the performance of dye-sensitized solar cells based on them. With the modification of conventional 4,4′-dicarboxylic-2,2′-bipyridyl anchoring ligands with phenyl-based bipyridine units, both RC dyes show superior photophysical and electrochemical properties, resulting in excellent device performance. Remarkably, with the enhancement of the electron-withdrawing ability of X, RC-76 has more satisfactory properties in absorption intensity, redox potential, electron transport and dye regeneration, which can be confirmed by UV-vis absorption spectroscopy, cyclic voltammetric measurement, density functional theory calculations and transient absorption spectroscopy. The devices based on RC-76 achieve a short-circuit current density of 17.52 mA cm−2 and a power conversion efficiency of 9.23%. The kinetics study and electrical impedance spectroscopy explain the causes of the inferior open-circuit voltage of RC dyes compared to that of standard Z907 dye. RC dyes, represented by RC-76, exhibit good long-term stability and the corresponding solar cells retain over 90% of the initial power conversion efficiency after 1000 h.

Design, Synthesis and Characterization of Amphiphilic Bipyridyl Ruthenium (II) Sensitizers

Dye-sensitized solar cells (DSC), as a new innovation technology, have developed very quickly in the past decade since the breakthrough was accomplished by attaching ruthenium polypyridyl complexes to high surface area titania film electrode. Gratzel and co-workers have developed DSC with the efficiency over 10% under AM 1.5 solar radiation using cis-Ru(dcbpy)2(NCS)2 (known as the N3 dye, Where dcbpy = 2,2′-bipyridyl-4,4′-dicarboxylic acid) as sensitizer, in conjunction with organic solvent electrolyte containing iodide/triiodide redox couple. However, the disadvantages of exhibiting high energy absorption bands which only harvest a fraction of visible light and easy desorption from the titanium dioxide surface have restrict the practical application of dye-sensitized solar cells.