The Effect of Hole Transport Material Pore Filling on Photovoltaic Performance in Solid-State Dye-Sensitized Solar Cells (original) (raw)
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ACS Nano, 2013
The internal transport and recombination parameters of solid-state dye-sensitized solar cells (ssDSCs) using the amorphous organic semiconductor 2,20,7,70-tetrakis(N,N-di-p-methoxyphenylamine)-9,90-spirobifluorene (spiro-MeOTAD) as a hole transport material (HTM) are investigated using electrical impedance spectroscopy. Devices were fabricated using flat and nanostructured TiO2 and compared to systems using nanostructured ZrO2 to differentiate between the transport processes within the different components of the ssDSC. The effect of chemically p-doping the HTM on its transport was investigated, and its temperature dependence was examined and analyzed using the Arrhenius equation. Using this approach the activation energy of the hole hopping transport within the undoped spiro-MeOTAD film was determined to be 0.34±0.02 and 0.40±0.02 eV for the mesoporous TiO2 and ZrO2 systems, respectively.
The Journal of Physical Chemistry C, 2014
Push−pull" structures have been considered a winning strategy for the design of fully organic molecules as sensitizers in dyesensitized solar cells (DSSC). In this work we show that the presence of a molecular excited state with a strong charge-transfer character may be critical for charge generation when the total energy of the photoexcitation is too low to intercept accepting states in the TiO 2 photoanode. Though hole transfer to the 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene can be very fast, an electron−hole pair is likely to form at the organic interface, resulting in a possible traplike excitation. This leads to poor photocurrent generation in the solid state DSSC (ss-DSSC) device. We demonstrate that it is possible to overcome this issue by fabricating SnO 2 -based ss-DSSC. The resulting solar cell shows, for the first time, that a SnO 2 -based ss-DSSC can outperform a TiO 2 -based one when a perylene-based, low-band-gap, push− pull dye is used as sensitizer. equally to this work. Figure 4. (a) Current/voltage characteristics under simulated solar conditions measured for ss-DSSC fabricated from either TiO 2 or SnO 2 nanoporous films sensitized with ID504 dye. As inset, the table reports the main figures of merit of the photovoltaic devices. (b) Photovolatic action spectra for TiO 2 -and SnO 2 -based DSSC incorporating ID504 as the sensitizer.
ACS Nano, 2012
We present the synthesis and device characterization of new hole transport materials (HTMs) for application in solid-state dye-sensitized solar cells (ssDSSCs). In addition to possessing electrical properties well suited for ssDSSCs, these new HTMs have low glass transition temperatures, low melting points, and high solubility, which make them promising candidates for increased pore filling into mesoporous titania films. Using standard device fabrication methods and Z907 as the sensitizing dye, power conversion efficiencies (PCE) of 2.94% in 2-μm-thick cells were achieved, rivaling the PCE obtained by control devices using the state-ofthe-art HTM spiro-OMeTAD. In 6-μm-thick cells, the device performance is shown to be higher than that obtained using spiro-OMeTAD, making these new HTMs promising for preparing high-efficiency ssDSSCs.
Materials Science and Engineering: B, 2014
TiO 2 nanotubes grown by anodic oxidation of Ti thin film deposited on conducting transparent fluoridedoped tin oxide (FTO) substrate were used as a unique geometrically organized template to study the infiltration of Spiro-MeOTAD hole transporting material (HTM) inside straight pores. The TiO 2 nanotube (TNT) array electrode was compared with a mesoporous one in terms of loading with an organic dye of high extinction coefficient. It was shown that it is possible to build a working solid state dye sensitized solar cell device with such a combination of materials and its performance was compared with a device in which the solid state HTM was replaced by a liquid state electrolyte.
Inorganica Chimica Acta, 2008
In this feature article, we discuss the key aspects of solid-state dye-sensitized solar cells (SDSC) and propose different concepts based on extensive studies carried out in our group to improve their performance. The influence of compact TiO 2 layer, novel donor-antenna sensitizing dyes, nature of nanocrystalline-TiO 2 layers and solid-state organic hole conductors on the performance of SDSC is discussed in this article. Both preparation and thickness of the compact TiO 2 layer were optimized using spray pyrolysis. The studies revealed that an optimum film thickness of 120-150 nm of compact TiO 2 yielded the best rectifying behavior and SDSC performance. The influence of three different mesoporous titania films, obtained from three different titania nanocrystals, prepared by sol-gel, thermal, and colloidalmicrowave process, was also studied and discussed here. The TiO 2 layer with the optimum pore volume and pore diameter ($44 nm) displayed the highest efficiency and IPCE in SDSC. The importance of pore size rather than high surface area for filling the mesoporous layer with solid-state hole conductor became evident from this study. A series of heteroleptic Ru(II) complexes carrying donor antenna moieties, namely, triphenylamine (TPA) or N,N 0 -bis(phenyl)-N,N 0 -bis(3-methylphenyl)-1,1 0 -biphenyl-4,4 0 -diamine (TPD), were synthesized and applied in SDSC. These novel donor-antenna dyes revealed spectacular performances of power conversion efficiencies in the range 1.5-3.4%, as measured under AM 1.5 spectral conditions. This was attributed to highly efficient light harvesting of these novel dyes and the improved charge-transfer dynamics at TiO 2 -dye and dye-hole conductor interfaces. Different low molecular weight and polymeric triphenyldiamines were synthesized and utilized as hole-transporting layers (HTL) in SDSC. Different studies showed that low molecular TPDs displayed better efficiency than polymeric counterparts due to their improved filling into the pores of nc-TiO 2 layer. Another interesting study revealed that an optimum driving force in terms of HOMO-level difference between the dye and HTL decides charge carrier generation efficiency. Recently, novel hole conductors with spiro-bifluorene-triphenylamine core for transporting holes and tetraethylene glycol side chains for binding lithium ions were synthesized and applied in SDSC. This work clearly emphasizes that Li + -salt is required at the TiO 2 /dye interface as well as in the bulk of HTL. It was also found that the addition of about 5-20% of these Li + -binding hole conductors and higher Li-salt (N-lithiotrifluoromethane sulfonamide) concentrations improved the SDSC performance. An improvement of about 120% in the solar cell efficiency as compared to the reference cells was achieved with an optimum composition of Li + -binding hole conductor and Li-salt.
Advanced Energy Materials, 2014
suffer from potential leakage problems associated with the volatile nature of the liquid electrolyte, limiting this technology for large-scale applications. [ 3 ] In an effort to address these issues, a p-type organic semiconductor termed 2,2′,7,7′-tetrakis-(N,N-dip -methoxyphenyl-amine)9,9′ spirobifl uorene (Spiro-OMeTAD) was developed to replace the liquid electrolyte as a redox couple in the fabrication of "solid-state" dye-sensitized solar cells (ssDSCs) by Bach et al. in 1998. [ 4 ] To date, the highest effi ciency of 7.2% for ssDSCs have been achieved using Spiro-OMeTAD as the hole transport material (HTM), which was reported by Nazeeruddin and co-workers. [ 5 ] Recently, Snaith and co-workers employed an organometallic halide perovskite with Spiro-OMeTAD as HTM obtained a record effi ciency of 15.4%. [ 6 ] However, previous studies have demonstrated that the low hole mobility and conductivity of Spiro-OMeTAD signifi cantly limits the device performance near the maximum power point in solar cell. [ 7,8 ] In addition, the lengthy synthetic route of Spiro-OMeTAD may make it impractical for large-scale application in ssDSCs. [ 9 ] More importantly, the substantial overpotential required for dye A series of triphenylamine-based small molecule organic hole transport materials (HTMs) with low crystallinity and high hole mobility are systematically investigated in solid-state dye-sensitized solar cells (ssDSCs). By using the organic dye LEG4 as a photosensitizer, devices with X3 and X35 as the HTMs exhibit desirable power conversion effi ciencies (PCEs) of 5.8% and 5.5%, respectively. These values are slightly higher than the PCE of 5.4% obtained by using the state-of-the-art HTM Spiro-OMeTAD. Meanwhile, transient photovoltage decay measurement is used to gain insight into the complex infl uences of the HTMs on the performance of devices. The results demonstrate that smaller HTMs induce faster electron recombination in the devices and suggest that the size of a HTM plays a crucial role in device performance, which is reported for the fi rst time.