Chunyang Jia

Phenothiazine–triphenylamine based organic dyes containing various conjugated linkers for efficient dye-sensitized solar cells

In order to increase the electron-donating ability of the donor part of the organic dye, two phenothiazine groups, as additional electron donors, were introduced into a triphenylamine unit to form a starburst donor–donor (2D) structure in this paper. Three new organic dyes (WD-6, WD-7 and WD-8) containing this starburst 2D structure and a 2-cyanoacetic acid acceptor linked by various conjugated linkers (benzene, thiophene, and furan) have been designed, synthesized and applied in dye-sensitized solar cells (DSSCs). The introduction of a phenothiazine group with a butterfly conformation in the triphenylamine donor parts has a good influence on preventing the molecular π–π aggregation due to the starburst 2D structure of the organic dye. The conjugated linker effects on the photophysical, electrochemical and photovoltaic properties of these organic dyes were investigated in detail. The DSSCs made with these organic dyes displayed remarkable overall conversion efficiencies, ranging from 4.90–6.79% under an AM 1.5 solar condition (100 mW cm−2). The best performance was found for organic dye WD-8, in which a furan group was the conjugated linker. It displayed a short-circuit current (Jsc) of 14.43 mA cm−2, an open-circuit voltage (Voc) of 682 mV, and a fill factor (ff) of 0.69, corresponding to an overall conversion efficiency of 6.79%. The different photovoltaic behaviors of the solar cells based on these organic dyes were further elucidated by the electrochemical impedance spectroscopy.

Influence of the antennas in starburst triphenylamine-based organic dye-sensitized solar cells: phenothiazine versus carbazole

A new starburst triphenylamine-based organic dye (WD-1) with phenothiazine units as antenna groups was designed and synthesized and the corresponding dye (WD-4) containing carbazole antennas for the purpose of comparison was also synthesized. They were successfully applied in dye-sensitized solar cells (DSSCs). The photophysical and electrochemical properties of the dyes were investigated by UV-vis spectrometry and cyclic voltammetry. Under standard global AM 1.5 solar conditions, the WD-1 sensitized solar cell gave a short circuit photocurrent density (Jsc) of 9.2 mA cm−2, an open circuit voltage (Voc) of 625 mV, a fill factor (ff) of 0.79, corresponding to an overall conversion efficiency η of 4.54%. Under the same conditions, the WD-4 sensitized cell gave a Jsc of 7.3 mA cm−2, an Voc of 603 mV, and a ff of 0.74, corresponding to an overall conversion efficiency of 3.26%. An increase in η of about 39% was obtained from WD-4 to WD-1. Our findings demonstrate that the introduction of phenothiazine units as antennas in triphenylamine-based dyes could improve photovoltaic performance compared with carbazole units as antennas in DSSCs.

Theoretical study of carbazole–triphenylamine-based dyes for dye-sensitized solar cells

Three carbazole-triphenylamine-based dyes (D1, D2, D3) are designed. The geometries, electronic structures, and electronic absorption spectra of these dyes are studied by DFT and TD-DFT. The calculated geometries indicate that these dyes are all noncoplanar, which can help to inhibit the close intermolecular π-π aggregation effectively. The LUMO and HOMO energy levels of these dyes can be ensuring positive effect on the process of electron injection and dye regeneration. The trend of the calculated HOMO-LUMO gaps nicely compares with the spectral data. The calculated results of these dyes demonstrate that these dyes can be used as potential sensitizers for TiO(2) nanocrystalline solar cells.

Novel organic sensitizers containing dithiafulvenyl units as additional donors for efficient dye-sensitized solar cells

In order to increase the electron-donating ability of the donor part of the organic dye, the dithiafulvenyl (DTF) group as an additional electron donor is introduced into a triphenylamine (TPA) unit to form a donor–donor (2D) structure in this paper. Two new organic dyes WD9 (one 2-cyanoacetic acid as an electron acceptor) and WD11 (two 2-cyanoacetic acids as electron acceptors) containing this DTF–TPA 2D structure are designed, synthesized and applied in dye-sensitized solar cells (DSSCs). It is found that the double donor structures (DTF–TPA) not only contribute to enhancement of the electron-donating ability, but also inhibit aggregation between dye molecules and prevent I3− in the electrolyte from recombining with injected electrons in TiO2. Under AM 1.5G irradiation (100 mW cm−2), a maximum power conversion efficiency (η) of 4.09% is obtained for the WD11-based DSSC, higher than that of DTF-free dye L0 (η = 2.47%). These results have demonstrated that the incorporation of the DTF group into the organic dye will be an effective approach to develop high-performance metal-free organic dyes.

A novel tri-layered photoanode of hierarchical ZnO microspheres on 1D ZnO nanowire arrays for dye-sensitized solar cells

A novel tri-layered ZnO nanostructure, which consists of ZnO nanowires (ZnO NWs) as the underlayer, small ZnO hierarchical microspheres (S-ZnO HMSs) as the intermediate layer and large ZnO hierarchical microspheres (L-ZnO HMSs) as the overlayer, was designed and studied as the photoanode for dye-sensitized solar cells (DSSCs). The photoanode was characterized by X-ray diffraction, scanning electron microscopy and its optical properties were measured by UV-vis spectrophotometry. The performance of the DSSC based on the photoanode was characterized by the incident-photon-to-current conversion efficiency (IPCE) and voltage–current curve (I–V). The results indicate that ZnO hierarchical microspheres show a good bifunctional character (light scattering effect and dye-loading ability), which causes the corresponding DSSCs based on the tri-layered ZnO photoanode to obtain the highest photovoltaic conversion efficiency (3.21%) compared with the DSSC based on the double layered ZnO photoanode and single layer ZnO NWs photoanode.

Dithiafulvenyl–triphenylamine organic dyes with alkyl chains for efficient coadsorbent-free dye-sensitized solar cells

Dithiafulvenyl–triphenylamine (DTF–TPA) based organic dyes with different alkyl chains attached on the DTF unit were examined to investigate the effect of alkyl chain lengths on the photovoltaic performances of dye-sensitized solar cells (DSSCs). Relative to WD9 with two methyl groups, the power conversion efficiency (η) increased significantly from 3.18% to 4.29% (WD12 with two hexyl chains) and 4.62% (WD13 with two decyl chains) in the absence of the chenodeoxycholic acid (CDCA). An increase in η of about 45.2% was obtained from WD9 to WD13. The attached longer alkyl chains in DTF–TPA based organic dyes are effective to suppress the electron recombination and reduce the interactions between dye molecules. Electrochemical impedance spectroscopy studies indicate that both the resistance for charge recombination and the electron lifetime are increased after the increase of alkyl chains length to the dye molecules. The η of DSSC based on WD9 was markedly increased by about 28.6% in the presence of CDCA as compared to that in the absence of CDCA. However, the η of WD13-sensitized DSSC was not dependent on CDCA and decreased by about 5.4% in the presence of CDCA. This work indicates that the incorporation of longer alkyl chains into DTF–TPA organic dyes is a promising way for efficient coadsorbent-free DSSCs.

Theoretical investigation of phenothiazine–triphenylamine-based organic dyes with different π spacers for dye-sensitized solar cells

Three phenothiazine-triphenylamine-based organic dyes (CD-1, CD-2 and CD-3) are designed based on the dye WD-8. The geometries, electronic structures, and electronic absorption spectra of these dyes before and after binding to TiO2 are studied by density functional theory (DFT) and time-dependent density functional theory (TD-DFT). The calculated geometries indicate that these dyes show good steric hindrance effect which is advantage to inhibit the close intermolecular π-π aggregation effectively. The lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) energy levels of these dyes could ensure positive effect on the process of electron injection and dye regeneration. The simulated spectra of CD-1∼3 show better absorption than that of WD-8 in the low energy zone. All the calculated results demonstrate that these dyes could be used as potential sensitizers for DSSCs and show better performances than WD-8.

Electrodeposition of V2O5 on TiO2 nanorod arrays and their electrochromic properties

This paper shows a simple approach for the electrodeposition of V2O5 nanoparticles on a TiO2 nanorod arrays substrate by combining hydrothermal and electrochemical deposition methods. The electrochemical and optical properties of the TiO2/V2O5 hybrid film have been investigated and the results show that the hybrid film has obviously better electrochemical and electrochromic properties compared with the single V2O5 thin film. The TiO2/4cir-V2O5 hybrid film shows the most improved electrochromic properties with excellent cyclic stability, outstanding transmittance modulation (50% at 780 nm) and high coloration efficiency (28 C−1 cm2 at 780 nm). The modified electrochromic properties are mainly due to the TiO2 nanorod array structure, which contributes to improve the structural stability of the V2O5 film and benefits the intercalation/deintercalation process of Li+ ions within the V2O5 film.

A Strategy To Boost the Efficiency of Rhodanine Electron Acceptor for Organic Dye: From Nonconjugation to Conjugation

Rhodanine-3-acetic acid is a very important and common electron acceptor of organic dye for dye-sensitized solar cells (DSSCs). However, the photovoltaic performances of organic dyes with rhodanine-3-acetic acid are relatively poor in the great majority of cases due to its nonconjugated structure between rhodanine ring and carboxyl anchoring group. Herein, a rhodanine derivative with conjugated structure between rhodanine ring and anchoring group is first employed as electron acceptor for TiO2-based DSSCs. Organic dye with this conjugated electron acceptor can not only maintain wide absorption spectrum but also greatly improve the electronic structure and adsorption geometry on TiO2, which significantly enhances the electron injection and slows the charge recombination. So the power conversion efficiency of DSSC based on organic dye CRD-I with this conjugated electron acceptor is increased by 2 times as compared with DSSC based on organic dye RD-I with nonconjugated rhodanine-3-acetic acid. Moreover, it is also found that CRD-I is superior to RD-I with respect to DSSC stability and binding ability to TiO2. This work unambiguously demonstrates that the conjugated rhodanine derivative is a highly promising electron acceptor and provides a new strategy for high-efficiency rhodanine-based organic dyes in DSSCs.

Toward high-efficiency, hysteresis-less, stable perovskite solar cells: unusual doping of a hole-transporting material using a fluorine-containing hydrophobic Lewis acid

Perovskite solar cells (PSCs) have demonstrated high power conversion efficiency (PCE) but inferior long-term stability and remarkable hysteresis. To date, the most efficient PSCs have a n–i–p device architecture and use Li-TFSI/t-BP as standard bi-dopants for the hole-transporting layer (HTL). However, such dopants not only induce deleterious effects on stability but also significantly affect the hysteresis of PSCs. Here, we demonstrate that a fluorine-containing hydrophobic Lewis acid dopant (LAD) can be employed as an effective dopant for PTAA to realize an exceptional fill factor of 0.81 and a record PCE as high as 19.01%, the highest value among the ever reported PSCs based on a novel dopant in the HTL, versus 17.77% for the control device with Li-TFSI/t-BP doped PTAA. To the best of our knowledge, this is the first case in which a PSC based on a novel dopant for the HTL shows higher efficiency than a PSC based on the state-of-the-art bi-dopants Li-TFSI/t-BP. Besides, the LAD-based PSC displays lower J–V hysteresis and much better long-term stability of up to 70 days under air exposure without encapsulation. We believe that this work will pave a new avenue for high-efficiency, hysteresis-less and stable PSCs exploring hydrophobic dopants as alternatives to hydrophilic Li-TFSI/t-BP.