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ZnO was known as a good electron transporting material for the planar perovskite solar cells (PSCs). The stability of perovskite cell based on ZnO electron transporting layer (ETL) however is not good, due to the basicity nature of ZnO, which will react with the proton on CH 3 NH 3 + of perovskite. Doping was used successfully to modify the physicochemical properties of ZnO to improve the performance. High quality, fully covered Al doped ZnO (AZO) thin (~20 nm) film on ITO substrate was successfully prepared by a sputtering method. Compared to the cell based on ZnO, perovskite cell using AZO as ETL has better stability, comparable Jsc, higher Voc and FF. The best AZO based perovskite cell achieves the highest power conversion efficiency of 17.6% with Voc of 1.07 V which the highest Voc for the perovskite solar cell based on ZnO ETL. The improvement in the photovoltaic performance was due to AZO has higher conductivity, more resistance to the acid and better band matching with MAPbI 3 compared to ZnO. The highly conducting and transparent AZO film was also used to replace ITO/ZnO as an anode as well as the ETL in the planer perovskite cell to achieve the PCE of 6.3%. [ABSTRACT FROM AUTHOR]

Abstract: Four donor–conjugated spacer–acceptor (D–π–A) organic dyes containing cyclopentadithiophene unit as a part of the conjugated spacer are prepared and studied to investigate the effects of the conjugated spacer and donor on the short-circuit current and conversion efficiency of the corresponding DSSCs. Theoretical calculations reveal that a shorter conjugated spacer or a stronger donor leads to more effective electron injection upon photo excitation. Therefore, D–π–A typed dye with longer conjugated spacer may have higher absorption coefficient and longer λ max. Nevertheless, it may also have lower effective electron injection upon photo excitation. Calculation data also show that cyclopentadithiophene although is a good moiety for extending the conjugation length of the organic dyes, it also acts as an electron sink, decreasing the effective electron injection. The transition probability calculated with the electron density difference analyses combining with the experimental absorption and photovoltaic performance data provides a useful protocol for designing organic photosensitizers for DSSCs at the electronic and structural levels. [Copyright &y& Elsevier]

Abstract: A series of conjugated/non-conjugated copolymers and their corresponding oligomers were prepared and their optical and physical properties were investigated for understanding the merit of blocking the conjugated chromophores with non-conjugated spacers. It was found that compared to the oligomers, copolymers have the advantages of amorphous nature, high thermal stability, and good thin film processability without sacrificing the quantum efficiency and purity of the emission color. Furthermore, based on the optical data of these copolymers and oligomers, the conjugation length of the polyoctylthiophene was estimated to be extended over 23–31 octylthiophene rings. [Copyright &y& Elsevier]

Abstract: Highly conducting porous polymer electrolytes comprised of poly(vinylidene-fluoride-co-hexafluoropropylene) (PVdF-HFP), polyethylene oxide-co-polypropylene oxide-co-polyethylene oxide (P123), ethylene carbonate (EC), propylene carbonate (PC), and LiClO4 were fabricated. The PVdF-HFP/P123 hybrid polymer membranes were made with a phase inverse method and the electrolyte solution uptake was carried out in glove box to avoid the moisture contamination. It was found that when a small amount of polymer surfactant (P123) was blended into the PVdF-HFP, mesopores with well-defined sizes were formed. Impedance spectroscopy showed that the room temperature conductivity of (PVdF-HFP)/P123 polymer electrolytes increased as the content of P123 increased up to 4×10−3 S/cm. Nitrogen adsorption isotherms, electrolyte solution uptake, porosity measurements, and SEM micrographs showed that the enhanced conductivity was due to increase the pore volume, pore density, and electrolyte uptake. The highest conduction was found when the weight ratio of P123 to PVdF-HFP was 70%, when big channels were formed in the hybrid polymer membrane. Furthermore, blending P123 in PVDF-HFP reduced the pore size of polymer membrane, therefore, the solution leakage was also reduced. These polymer electrolytes were stable up to 4.5V (vs Li/Li+) and the performance of the model lithium ion battery made by sandwiching the polymer electrolyte between a LiCoO2 anode and a MCMB cathode, showed great promise for the use of these polymer electrolytes in lithium ion batteries. [Copyright &y& Elsevier]

Abstract: Starting from 2,6-bis-(3-octylthiophene-2yl)-pyridine, two new poly(alkylthiophene) derivatives, POTPyOT and POTPy, containing pyridine in the backbone were prepared from nickel(0)-mediated Stille coupling or by palladium-catalyzed Yamamoto coupling. These polymers exhibited good solubility in common organic solvents, thermal stability up to 400°C, and facile film formation. They were amorphous and give strong luminescence both in CHCl3 solution and solid state film. The polymers emitted blue light in solution with photoluminescence (PL) emission maximum at 420–484nm and green light with PL emission maximum at 500–514nm in thin films. These polymers showed a reversible redox reaction at potential from 0 to 1.3V (vs. SCE). Nevertheless, the reduced form of the polymer was very unstable; it decomposed in the presence of oxygen or water. The emission and UV–vis absorption of the polymer were influenced by the solvent polarity, protonation, and acid–base treatment. These may be the results of the stabilization of the polar excited state by solvation and the change of the conformation in polymer backbone. Electroluminescence (EL) was achieved from a single-layer PLED with the configuration of ITO/POTPyOT/Al. The turn-on voltage of the device is 10V and the λ max (550nm) of the EL is voltage independent. [Copyright &y& Elsevier]

The physicochemical properties and photo catalytic activity of transition metal-loaded TiO2 catalysts were studied. The transition metal was deposited on TiO2 via post-hydrothermal synthesis and photo-assisted reduction/impregnation. The structure of TiO2 is preserved upon adding Pd, Cr, and Ag into it. Nevertheless, the structure of TiO2 was destroyed when reacted with silicotungstic acid (Si-W). As a consequence, under the irradiation of visible light, the Pd and Cr loaded TiO2 showed higher photo catalytic activity compared to pristine TiO2 and Si-W loaded TiO2 has no catalytic activity, although the threshold absorptions of all metal loaded TiO2 is similar to that of pure TiO2. Transition metal was homogeneously coated on the TiO2 particles and there is no phase separation between metal salts and TiO2 as revealed with scanning electron micrographs (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) data. X-ray photoelectron spectroscopy (XPS) spectra showed that all metals in metal loaded TiO2 presented as an ionic state with slightly reduction compared to the metal in metal salt used in the reaction, probably due to the interaction with TiO2. These results suggested that the crystallinity was important for the photo catalytic activity of TiO2 based catalysts and the function of transition metal is to increase the electron-hole recombination time, therefore increase the catalytic activity. [Copyright &y& Elsevier]

A new type of TiO2 film is prepared by insertion of a bifunctional silane agent bearing sulfonate group in between TiO2 and the substrate. The alkoxyl silane is bound to the surface of the substrate via molecular self-absorption and the terminal sulfonate group is used to grasp the TiO2 particles to form stable film. Modifications of the TiO2 catalysts, such as metal deposition and calcination, were carried out simply with the films on substrates. The activity of this new type TiO2 film is tested by catalytic photodegrading of salicylic acid in water. It was found that when the particle size of the TiO2 is smaller than 200 nm, the catalytic activities of the TiO2 films deposited on sulfonate-grafted glass are better than those of the films deposited on unmodified glass. Increasing the crystallinity of TiO2 particles, depositing the precious metals (such as Au or Pd) on TiO2, or aging the TiO2 film will enhance the catalytic activity of TiO2. The enhancement is better for the film deposited on sulfonate-grafted substrates. In spite of calcining the TiO2 film decreased its catalytic activity due to the particle aggregation, the decrease is also less significant for TiO2 films deposited on sulfonate-grafted substrates. The sulfonate group can be regarded as a dispersion agent for TiO2 film deposition and calcination. [Copyright &y& Elsevier]

Five monochloro- s -triazinyl reactive dyes (MCT) and five m -carboxypyridium- s -triazinyl reactive dyes (NTR) were synthesised with the same red chromophore bearing an –NHCN, –OCH 3 , –CH 3 NSO 2 CH 3 , – N -methyl phenyl or –OH group as 'second-leg' substituents. A kinetic study of the hydrolysis of these dyes was conducted, and the rate constant (k obs) and half-life time values were determined. The k obs of the MCT and NTR dyes was found to follow the order –OCH 3 > –CH 3 NSO 2 CH 3 > – N -methyl phenyl > –NHCN > –OH, which was approximately in agreement with the values obtained for the Hammett substituent constants. Overall, the higher the electron-donating property of the substituent on meta -position to the leaving group in the triazine ring, the lower the hydrolysis rate constant. • Chloro substituent in the MCT dyes was replaced by nicotinic acid, the reactivity was enhanced. • The order of reactivity of dyes is related to the electronic effect of the substituent. • The order of k obs was in agreement with the values of Hammett substituent constants. [ABSTRACT FROM AUTHOR]

An antisolvent (iodobenzene, IB) was used to assist the formation of closely packed CH 3 NH 3 PbI 3 (MAPbI 3 ) thin films during the one-step spin-coating process using different volumes of IB. The morphological, structural, optical and excitonic properties of MAPbI 3 thin films were analyzed using a contact-mode atomic-force microscope, X-ray diffractometer, broadband absorbance spectrometer and optical microscope-based time-resolved photoluminescence spectrometer. The properties of the resultant MAPbI 3 thin films can be manipulated by using different IB volumes, which dominates the device performance of MAPbI 3 based photovoltaic cells. The experimental results show that the grain size (or particle size) of MAPbI 3 thin films influences the collection of photoexcited carriers and the contact at the 6,6-Phenyl C 61 butyric acid methyl ester (PCBM)/MAPbI 3 interface, thereby resulting in a trade-off between the fill factor (FF) and short-circuit current density (J SC ). In addition, it is predicted that the power conversion efficiency (PCE) can be further improved by increasing the crystallinity of the MAPbI 3 thin film while keeping the small grain size. [ABSTRACT FROM AUTHOR]

Comprehensive studies were carried out to explore the roles of phenyl-C 61 -butyric acid methyl ester (PCBM) thin films in inverted-type CH 3 NH 3 PbI 3 (MAPbI 3 ) based photovoltaics, including the surface morphologies, transmittance spectra, photoluminescence spectra, X-ray diffraction (XRD) patterns, Raman scattering spectra and thin-film residual stress analysis. The reduction in the photoluminescence line width indicates that the crystallinity of the MAPbI 3 thin film can be increased by covering it with the PCBM thin film. The XRD patterns and Raman scattering spectra show a reduction in the compressive stress of MAPbI 3 thin film when covered by the PCBM thin film. In addition, it is noted that the residual stress at the contact interface between the hydrophilic MAPbI 3 and the hydrophobic PCBM can be ignored as confirmed by the results obtained with a home-made Twyman-Green interferometer. Consequently, the superior optoelectronic properties of the perovskite materials, as well as the use of a multifunctional fullerene-based thin film as the capping layer allow for the high-efficiency perovskite photovoltaics. [ABSTRACT FROM AUTHOR]

Comprehensive studies were carried out to explore the thickness-dependent characteristics of thermally evaporated C 60 thin films. The structural, optical, electronic and surface properties of the resultant C 60 thin films were analyzed using Raman scattering spectrometry, photoluminescence spectroscopy, absorbance spectroscopy, photoelectron emission spectrometry and water droplet contact angle measurement. The experimental results show that the thickness of the C 60 thin film has a decisive impact on the photovoltaic performance of CH 3 NH 3 PbI 3 based solar cells in terms of open-circuit voltage (V OC ), short-circuit current density (J SC ) and fill factor (FF). In the case of the 2.5 nm-thick C 60 film, the solar cells have the better V OC and J SC , as the results of the lower electron affinity and higher transparency. The FF of the solar cell is related to the coverage of C 60 on the transparent conductive electrode (TCE) and the CH 3 NH 3 PbI 3 perovskite continuity. Consequently, the photovoltaic performance can be expected to be improved by using a smooth TCE. [ABSTRACT FROM AUTHOR]

A series of alcohols (methanol, ethanol and isopropyl alcohol) were added to poly(3,4-ethylenedioxythiophene): (polystyrene sulfonate) (PEDOT: PSS) aqueous solutions in order to manipulate the molecular structure of the PEDOT chains in PEDOT: PSS hole transporting materials (HTMs) and thus to improve the power conversion efficiency of CH 3 NH 3 PbI 3 based solar cells. The structural and electronic characteristics of the resultant PEDOT: PSS HTMs were analyzed using atomic-force microscopy, contact angle measurement, Raman scattering spectrometry and photoelectron spectrometry. The properties of the PEDOT: PSS thin films could be controlled by tuning the viscosity of the PEDOT: PSS solutions. High viscosity PEDOT: PSS solutions resulted in linear structured PEDOT chains, which increased the work function of the PEDOT: PSS HTMs thereby improving the open-circuit voltage of the CH 3 NH 3 PbI 3 solar cells. The surface roughness and surface free energy of the PEDOT: PSS HTMs influence the structural properties of CH 3 NH 3 PbI 3 thin films, which determines the exciton dissociation at the CH 3 NH 3 PbI 3 /PEDOT: PSS interface (short-circuit current density) and the carrier recombination at the CH 3 NH 3 PbI 3 /[6,6]-phenyl-C61-butyric acid methyl ester (PC 61 BM) interface (fill factor). In addition, it is predicted that the power conversion efficiency can be further improved by increasing the crystallinity of the CH 3 NH 3 PbI 3 thin film. [ABSTRACT FROM AUTHOR]

A series of nonpolar antisolvents (chlorobenzene, bromobenzene, iodobenzene and toluene) were used to assist in the formation of smooth and crystalline CH 3 NH 3 PbI 3 thin films by a one-step spin-coating method. The structural, optical and excitonic characteristics of the resultant CH 3 NH 3 PI 3 thin films were analyzed using an atomic-force microscope, X-ray diffractometer, absorbance spectrum, photoluminescence (PL) spectrum, time-resolved PL and temperature-dependent PL. The properties of the CH 3 NH 3 PbI 3 thin films are dependent on the relative polarity and boiling point of the nonpolar antisolvents used in the washing treatment process. The interplay between nucleation (relative polarity) and crystal growth (boiling point) during the formation of CH 3 NH 3 PbI 3 thin films influences the short-circuit current density (J SC ) and power conversion efficiency (PCE) of the corresponding solar cells. The experimental results demonstrate that iodobenzene can be substituted for toluene as a more efficient antisolvent in the washing treatment process during the fabrication of CH 3 NH 3 PbI 3 thin films. In addition, it is predicted that the J SC and PCE can be further improved by increasing the crystallinity of the CH 3 NH 3 PbI 3 thin film. [ABSTRACT FROM AUTHOR]

The multicrystalline grain size of CH 3 NH 3 PbI 3 thin films can be manipulated by using different precursor concentrations which dominate the competition between the nucleation and crystal growth during the one-step spin-coating process with the toluene washing treatment. A comprehensive study was carried out to explore the correlation between the structural properties and the exciton dynamics in CH 3 NH 3 PbI 3 thin films fabricated using various precursor concentrations from 1.25 M to 1.65 M. The experimental results show that the precursor concentration influences the grain size and exciton dynamics of the resultant CH 3 NH 3 PbI 3 thin films which were fabricated on top of poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate/ITO/glass substrates. The higher average power conversion efficiency (PCE) of 13.66% achieved can be explained as being due to the formation of a larger CH 3 NH 3 PbI 3 grain size which thus results in higher photocurrent generation and lower voltage loss. It is predicted that the PCE can be further improved when the voltage loss across the CH 3 NH 3 PbI 3 thin film is minimized. [ABSTRACT FROM AUTHOR]

Inverted-type perovskite solar cells offer the potential of fabrication by low-temperature solution processing as an alternative to conventional-type perovskite solar cells. PEDOT:PSS is commonly used as the hole transport layer (HTL), but its acidic nature may damage the reliability and stability of the photovoltaic device. In this study, we demonstrate the use of MoO x and WO x HTLs as an alternative to PEDOT:PSS for planar CH 3 NH 3 PbI 3 perovskite solar cells. Furthermore, the MoO x and WO x HTLs are treated using a UV-ozone treatment to improve the surface coverage of the perovskite layer. The resultant conversion efficiency (PCE) for the best cells at AM1.5G illumination with a shadow mask was 13.1%. [ABSTRACT FROM AUTHOR]

Cobalt selenide (Co 0.85 Se) and nickel selenide (Ni 0.85 Se) hierarchical thin films assembled using by nanosheets and nanoparticles, respectively, were fabricated in situ on fluorine-doped tin oxide substrates in a ligand-free environment to prepare counter electrodes (CEs) for dye-sensitized solar cells (DSSCs) consisting of a N719-sensitized nanocrystalline TiO 2 film. The Co 0.85 Se- and Ni 0 . 85 Se-based CEs were rapidly synthesized via a microwave-assisted one-step method at 170 °C within a short reaction time of 10 min. The morphology and structure of the Co 0.85 Se and Ni 0.85 Se hierarchical thin films were characterized by means of scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The results of electrochemical impedance spectroscopy, cyclic voltammetry, and Tafel polarization measurements showed that both CEs exhibited good electrocatalytic activity and I − /I 3 − redox reactions and much lower charge-transfer resistance. A power conversion efficiency (PCE) of 8.58% for the Co 0.85 Se CE-based solar cell was obtained, which is comparable to that of cells using Pt CEs (8.57%); 7.09% PCE was obtained for the Ni 0.85 Se-based CE. The results suggest that in situ-prepared Co 0.85 Se-based CEs could be a promising alternative to Pt-based CEs for DSSCs. [ABSTRACT FROM AUTHOR]

Doping metal-ion into TiO 2 materials is an effective method for enhancing the performance of dye-sensitized solar cells (DSSCs). In order to develop materials that are easy to produce even in industrial quantities, we established a facile method by hydrothermal synthesis and subsequent heat treatment to prepare bismuth doped titanium dioxide nanofibers (Bi-doped TiO 2 NFs). At first, we adopt Bi-doped TiO 2 NFs as the working electrode to further study in DSSCs. Serving as working electrode, Bi-doped TiO 2 NFs can remarkably improve open-circuit voltage ( V OC ). The V OC was significantly enhanced from 0.633 V to 0.800 V compared with pristine TiO 2 does. However, this leads to a smaller J SC and a poorer overall performance for such devices. In order to improve the performance of DSSCs, we adopt Bi-doped TiO 2 NFs as the scattering layer of DSSCs, and various thicknesses of meso-TiO 2 nanoparticles (meso-TiO 2 NPs) were used as working electrode to increase the short-circuit current ( J SC ). The incorporated Bi-doped TiO 2 NFs can help the electron transport and may reduce the possibility for electron–hole recombination. After optimizing the device’s parameter, the overall performance of the meso-TiO 2 NPs/Bi-doped TiO 2 NFs devices was dominated by J SC until a maximum efficiency was attained with a meso-TiO 2 NPs thickness of 12 μm. Such optimized DSSCs exhibited high open circuit voltage of 0.787 V, high fill factor of 78.2%, and high power conversion efficiency of 8.89%. [ABSTRACT FROM AUTHOR]

A phase-pure mixed-organic-cation perovskite absorber (MOC-PA) was fabricated by a one-step spin-coating process with a toluene washing treatment, and the structural, optical and excitonic properties of the resultant MOC-PAs were then characterized by scanning electron microscopy, X-ray diffractometry, absorbance spectrometer, and time-resolved photoluminescence. The averaged power conversion efficiency (PCE) of inverted phase-pure MOC-PA based photovoltaics could be improved from 12.21% to 13.28% by tailing the surface roughness of the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) thin film from 1.43 nm to 1.84 nm. The improved PCE is mainly due to the increased short-circuit current density ( J SC ) which is attributed to the improvement of the exciton dissociation, as confirmed by photoluminescence experiments. In addition, the experimental results indicate that the PCE can be further improved by increasing the crystallinity of MOC-PAs. [ABSTRACT FROM AUTHOR]

A comprehensive study was carried out to understand the influence of organic cations on high-performance CH 3 NH 3 PbI 3 based photovoltaics. Scanning electron microscope, X-ray diffractometer, Hall measurement, absorbance spectrum, photoluminescence (PL) spectrum and nanosecond time-resolved PL measurements were used to explore the structural, electrical, optical and excitonic characteristics of CH 3 NH 3 PbI 3 thin films fabricated under different thermal annealing temperatures from 60 °C to 140 °C. The decrease in the open-circuit voltage ( V OC ) with an increase in the thermal annealing temperature can be explained as due to the reduced work function of the CH 3 NH 3 PbI 3 thin film. The short-circuit current density ( J SC ) of the CH 3 NH 3 PbI 3 based photovoltaics is dependent on the efficiencies of light absorption and carrier collection, which results in an optimized J SC when the thermal annealing temperature is 120 °C. The atomistic interaction between the organic cations and Pb–I framework strongly influences the absorbance of CH 3 NH 3 PbI 3 thin films, as confirmed by the libration of CH 3 NH 3 cations shown by Raman scattering spectroscopy. In addition, the experimental results indicate that the power conversion efficiency can be further improved when the absorption strength of the CH 3 NH 3 PbI 3 thin film and the energy-level alignment of each photovoltaic layer are simultaneously fulfilled. [ABSTRACT FROM AUTHOR]

Two diketopyrrolopyrrole (DPP) containing D–π–A organic dyes, named as TEDBn and TEDTh were prepared. Their optical, electrochemical and photophysical properties were investigated and their application in dye-sensitized solar cells (DSCs) was demonstrated. The broaden absorption and low-energy λ max of DPP containing dyes were contributed from DPP bridge and EDOT π-conjugated moiety. Compared to TEDTh, TEDBn has smaller absorption coefficient and higher optical bandgap. Nevertheless the power conversion efficiency (PCE) of TEDBn based DSC is 7.2% which is larger than that of TEDTh based DSC and 90% of N719 based cell. The higher PCE of TEDBn based device originates from both higher open-circuit voltage (V OC ) and short-circuit current (J SC ). Femtosecond time-resolved photoluminescence data show that the electron injection at TEDBn/TiO 2 is more efficient than that at TEDTh/TiO 2 interface, resulting in higher J SC (and IPCE) of TEDBn based DSC. Density function theory (DFT) calculations revealed that TEDBn is a linear structure which leads to higher dye loading on TiO 2 than TEDTh which featured a bend conformation, better TiO 2 surface coverage, resulting in larger V OC . Therefore, the overall efficiency of the cell sensitized by TEDBn is better than that the devices based on TEDTh. [ABSTRACT FROM AUTHOR]

This work studies annealing effects of the CH 3 NH 3 PbI 3 perovskite film for solar cell applications by time-resolved photoluminescence (TR-PL) spectra. The different thermal annealing temperatures process influences the quality and exciton lifetime of the CH 3 NH 3 PbI 3 perovskite film and importantly the device performance. The CH 3 NH 3 PbI 3 perovskite film of the optimal thermal annealing temperatures (100 °C) would significantly extended exciton lifetime and yield a higher open-circuit voltage, with short-circuit current density ( J SC ) = 21.58 mA/cm 2 , open-circuit voltage ( V OC ) = 0.84 V, fill factor (FF) = 61.4%, and η = 11.12%, respectively. [ABSTRACT FROM AUTHOR]

The open-circuit voltage of CH 3 NH 3 PbI 3 based photovoltaics was enhanced from 0.77 V to 0.9 V, which resulted in an improvement of the average power conversion efficiency from 5.63% to 11.74% achieved by tuning the work function of the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole transport layer. The higher work function of the PEDOT:PSS (1:20 wt%) thin film, as compared to the PEDOT:PSS (1:6 wt%) and PEDOT:PSS (1:2.5 wt%) thin films, was observed using photoelectron spectrometer. The carrier density of PEDOT was obtained by analyzing the transmittance spectrum of PEDOT:PSS/glass with the transfer matrix method. The Drude model can be used to explain the increased work function of the PEDOT:PSS thin film obtained by decreasing the ratio of PEDOT to PSS. The increased carrier density of the PEDOT in PEDOT:PSS thin films originated from conformational changes in the PEDOT chains as confirmed by Raman scattering spectroscopy. [ABSTRACT FROM AUTHOR]

A comprehensive study was carried out to understand the formation of a crystalline tri-iodide perovskite absorber (TPA) on top of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). Scanning electron microscopy, two-dimensional X-ray diffraction and nanosecond time-resolved photoluminescence were used to explore the correlation between the surface morphology and the exciton lifetime in TPA fabricated with and without the in-situ toluene washing treatment. The toluene washing treatment decreases the crystallinity (exciton lifetime) of TPA and improves the TPA coverage on the non-crystalline PEDOT:PSS surface. The high average power conversion efficiency (PCE) of 10.61% achieved can be explained as due to the efficient exciton dissociation at the interface between the TPA and the PEDOT:PSS. The experimental results show that the PCE can be further improved when the crystallinity of TPA and the TPA coverage on PEDOT:PSS are simultaneously optimized. [ABSTRACT FROM AUTHOR]

Comprehensive studies were carried out to understand the thickness effects of ZnO thin films for tri-iodide perovskite absorber (TPA) based photovoltaics, including the absorption spectrum, photoluminescence, nanosecond time-resolved photoluminescence (NTRPL), and photo-induced absorption (PIA) of TPA/ZnO/ITO/glass. These were carried out in order to explore the Urbach energy of TPA films and the exciton dissociation at the interface between TPA and ZnO. The results show that the thickness of the ZnO thin film significantly influences the photovoltaic performance in terms of open-circuit voltage ( V OC ), fill factor (FF), and short-circuit current density ( J SC ). In the case of the thicker ZnO film, the photovoltaics have the better FF and V oc , as a result of the smaller electron recombination. This means that a thicker ZnO film can block the electron recombination from the Fermi level of the ITO to the valance band of the TPA. On the other hand, the thicker ZnO film results in a higher J SC due to the better exciton dissociation at the interface between TPA and ZnO, which means that the electron mobility of the thicker ZnO is higher. Consequently, the photovoltaic performance can be expected to be improved by using a transparent cathode electrode with high conductivity and electron mobility. [ABSTRACT FROM AUTHOR]

Highlights: [•] Ionic liquids (ILs) were modified and used in dye-sensitized solar cells (DSSCs). [•] Various carbon derivatives were added in the IL electrolytes. [•] Carbon derivatives provided the additional pathway for charge transportation. [•] Efficient quasi-solid-state DSSCs were achieved by using CYC-B6S dye. [ABSTRACT FROM AUTHOR]

Abstract: An efficient back-illuminated dye-sensitized solar cell (DSSC) is made with a flexible Ti-foil based photoanode composed of a composite TiO2 film with TiO2 nanotubes (TNT) and TiO2 nanoparticles (TNP). The composite TiO2 film is fabricated through a novel dipping–rinsing–hydrolysis (DRH) process by inserting TiO2 into TNT and sintering the product to form TNP inside TNT. By directly placing TiO2 nanoparticles into TNT, the former grow internally from the base of TNT to occupy it completely. This solves previous problems of incomplete filling of TNP into TNT, which used partial penetration of TiCl4 reactant from the top of the TNT. In the present case, the TNP are grown from the base of TNT. A DSSC containing TNT and TNP prepared in this way shows a photoelectric efficiency of 6.45%, which is much higher than that (4.21%) of a DSSC with untreated TNT. The films are characterized by using scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The improvement in the photoelectric efficiency is explained by using electrochemical impedance spectroscopy (EIS), incident photon-to-current conversion efficiency (IPCE) analysis, and UV-absorption spectra analysis. [Copyright &y& Elsevier]