An investigation of the function of an indolene‐based organic dye, termed D149, incorporated in to solid‐state dye‐sensitized solar cells using ...2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxypheny‐amine)‐9,9′‐spirobifluorene (spiro‐OMeTAD) as the hole transport material is reported. Solar cell performance characteristics are unprecedented under low light levels, with the solar cells delivering up to 70% incident photon‐to‐current efficiency (IPCE) and over 6% power conversion efficiency, as measured under simulated air mass (AM) 1.5 sun light at 1 and 10 mW cm−2. However, a considerable nonlinearity in the photocurrent as intensities approach “full sun” conditions is observed and the devices deliver up to 4.2% power conversion efficiency under simulated sun light of 100 mW cm−2. The influence of dye‐loading upon solar cell operation is investigated and the thin films are probed via photoinduced absorption (PIA) spectroscopy, time‐correlated single‐photon counting (TCSPC), and photoluminescence quantum efficiency (PLQE) measurements in order to deduce the cause for the non ideal solar cell performance. The data suggest that electron transfer from the photoexcited sensitizer into the TiO2 is only between 10 to 50% efficient and that ionization of the photo excited dye via hole transfer directly to spiro‐OMeTAD dominates the charge generation process. A persistent dye bleaching signal is also observed, and assigned to a remarkably high density of electrons “trapped” within the dye phase, equivalent to 1.8 × 1017 cm−3 under full sun illumination. it is believed that this localized space charge build‐up upon the sensitizer is responsible for the non‐linearity of photocurrent with intensity and nonoptimum solar cell performance under full sun conditions.
An indolene‐based dye performs remarkably well in solid‐state dye‐sensitized solar cells, delivering 6% efficiency measured under simulated solar illumination of 10 mW cm−2. The photovoltaic process is shown to proceed via reductive quenching, which has not previously been observed to be the dominant process in efficiently operating dye‐sensitized solar cells.
In oxygenic photosynthetic eukaryotes, the hydroxylated carotenoid zeaxanthin is produced from preexisting violaxanthin upon exposure to excess light conditions. Zeaxanthin binding to components of ...the photosystem II (PSII) antenna system has been investigated thoroughly and shown to help in the dissipation of excess chlorophyll-excited states and scavenging of oxygen radicals. However, the functional consequences of the accumulation of the light-harvesting complex I (LHCI) proteins in the photosystem I (PSI) antenna have remained unclarified so far. In this work we investigated the effect of zeaxanthin binding on photoprotection of PSI–LHCI by comparing preparations isolated from wild-type Arabidopsis thaliana (i.e., with violaxanthin) and those isolated from the A . thaliana nonphotochemical quenching 2 mutant, in which violaxanthin is replaced by zeaxanthin. Time-resolved fluorescence measurements showed that zeaxanthin binding leads to a previously unrecognized quenching effect on PSI–LHCI fluorescence. The efficiency of energy transfer from the LHCI moiety of the complex to the PSI reaction center was down-regulated, and an enhanced PSI resistance to photoinhibition was observed both in vitro and in vivo. Thus, zeaxanthin was shown to be effective in inducing dissipative states in PSI, similar to its well-known effect on PSII. We propose that, upon acclimation to high light, PSI–LHCI changes its light-harvesting efficiency by a zeaxanthin-dependent quenching of the absorbed excitation energy, whereas in PSII the stoichiometry of LHC antenna proteins per reaction center is reduced directly.
The recent success of lead halide perovskites is given by their optimal primary optoelectronic properties relevant for photovoltaic and, more in general, for optoelectronic applications. However, a ...lack of knowledge about the nature of instabilities currently represents a major challenge for the development of such materials. Here we investigate the luminescence properties of polycrystalline thin films of lead halide perovskites as a function of the excitation density and the environment. First we demonstrate that in an inert environment photoinduced formation of emissive sub-band gap defect states happens, independently of the chemical composition of the lead halide semiconductor, which quenches the band-to-band radiative emission. Carrier trapping occurs in the subnanosecond time regime, while trapped carriers recombine in a few microseconds. Then, we show that the presence of oxygen, even in a very small amount, is able to compensate such an effect.
We have fabricated CH3NH3PbI3−xClx perovskite thin films crystallized in situ on substrates of different natures (e.g., porosity, wettability) and investigated their photoluminescence properties. We ...observe that the crystallization time and thin film structure are strongly influenced by the chemical nature and porosity of the substrate. Moreover, we find that the mesoporous scaffold can tune the emissive properties of the semiconducting compound both in terms of spectral region and dynamics. In particular, perovskite crystallites grown in the nanometre size porous scaffold present a shorter-living and blue-shifted emission with respect to the perovskite crystals which are free to grow without any constraints.
Commercialization of lead halide perovskite-based devices is hindered by their instability towards environmental conditions. In particular, water promotes fast decomposition, leading to a drastic ...decrease in device performance. Integrating water-splitting active species within ancillary layers to the perovskite absorber might be a solution to this, as they could convert incoming water into oxygen and hydrogen, preserving device performance. Here, we suggest that a CuSCN nanoplatelete/p-type semiconducting polymer composite, combining hole extraction and transport properties with water oxidation activity, transforms incoming water molecules and triggers the in situ p-doping of the conjugated polymer, improving transport of photocharges. Insertion of the nanocomposite into a lead perovskite solar cell with a direct photovoltaic architecture causes stable device performance for 28 days in high-moisture conditions. Our findings demonstrate that the engineering of a hole extraction layer with possible water-splitting additives could be a viable strategy to reduce the impact of moisture in perovskite devices.
The poor environmental stability of lead halide perovskites limits their performance in solar cells. Here, a CuSCN nanoplateletes/p-type semiconducting polymer composite layer enables the stable performance of a solar cell for 28 days in high-moisture conditions, attributed to water splitting.
Organic conductors are being evaluated for potential use in waste heat recovery through lightweight and flexible thermoelectric generators manufactured using cost-effective printing processes. ...Assessment of the potentiality of organic materials in real devices still requires a deeper understanding of the physics behind their thermoelectric properties, which can pave the way toward further development of the field. This article reports a detailed thermoelectric study of a set of highly conducting inkjet-printed films of commercially available poly(3,4-ethylenedioxythiophene) polystyrene sulfonate formulations characterized by in-plane electrical conductivity, spanning the interval 10–500 S/cm. The power factor is maximized for the formulation showing an intermediate electrical conductivity. The Seebeck coefficient is studied in the framework of Mott’s relation, assuming a (semi-)classical definition of the transport function. Ultraviolet photoelectron spectroscopy at the Fermi level clearly indicates that the shape of the density of states alone is not sufficient to explain the observed Seebeck coefficient, suggesting that carrier mobility is important in determining both the electrical conductivity and thermopower. Finally, the cross-plane thermal conductivity is reliably extracted thanks to a scaling approach that can be easily performed using typical pump–probe spectroscopy.
In this work, we report a library of thirteen fluorinated ionic liquids consisting of iodide salts of 1-alkyl-3-polyfluoroalkyl-imidazolium cations. By changing the length of the alkyl and ...polyfluoroalkyl pendants, we discovered that particular combinations of these result in compounds showing a mesophase. The nature and the molecular arrangement of the mesophase are characterised by polarised optical microscopy and powder X-ray diffraction analysis, among others. We demonstrate that, after the addition of I sub(2) to generate the I super(-)/I sub(3) super(-) redox couple, anisotropic ionic conductivity takes place along preferential pathways in the lamellar structure of the mesophase. Notably, the addition of I sub(2) does not suppress the mesophase temperature range, contrary to previously reported systems. Furthermore, the tendency of these materials to supercool allows the molecular arrangement in the mesophase to be retained in a solid film at ambient temperatures. Finally, we demonstrate their applicability as a quasi-solid electrolyte by preparing dye-sensitised solar cells with power conversion efficiencies comparable to the previous reports.
In the version of this Article originally published, the units of the Fig. 3a x axis were incorrectly given as meV. They should have been eV. This has now been corrected in all versions of the ...Article.
We show that pristine thin films made of tin halide perovskite have external photoluminescence quantum yield comparable to that of lead halide perovskite, i.e., the material in use to prepare ...state-of-the-art perovskite solar cells.
We quantify the role of many-body elastic scattering effects on exciton dephasing rates in two-dimensional hybrid metal-halide perovskites by means of nonlinear coherent excitation spectroscopy at a ...temperature of 5 K. We find that the exciton-density dependence of excitation-induced dephasing (EID) is two to three orders of magnitude lower than in other atomic monolayer semiconductors such as transition metal dichalchogenides. Furthermore, EID is different for the multiple excitons evident in the excitation line shape, as is their phonon-mediated temperature dependence. We ascribe these observations to screening effects due to polaronic dressing by the lattice.
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