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The tunability of the carrier/conduction polarity of halide perovskite via intrinsic defect self-doping makes it possible to implement a simple p–n heterojunction perovskite solar cell. Here, approaching 16% efficient prototype device of the p-type spiro-MeOTAD/n-type MAPbI3 heterojunction perovskite solar cell is demonstrated via synergetic energy band and interface engineering. The n-type perovskite is enabled by self-doping associated with excess PbI2, avoiding a redundant electron transport layer, while the oxygen-induced p-type extrinsic doping (oxidation) of spiro-MeOTAD ensures its high hole conductivity and Ohmic contact with Au back electrode. Furthermore, ITO's effective work function is reduced by the polar molecular modification layer to ensure its Ohmic contact with perovskite. Also, the functional groups of this modification layer effectively passivate the front interface defects, contributing to the enhanced device performance observed. This work highlights the great potential of facile energy band and interface engineering for efficient and simple-structured perovskite solar cells. [ABSTRACT FROM AUTHOR]

We report a solution-based method to prepare a hybrid carbon materials consisted of carbon nanotubes modified graphite/carbon black as a low-cost platinum-free counter electrode for dye-sensitized solar cell (DSSC). The effects of carbon nanotube content on the performance of counter electrode are examined. The 25 wt% carbon nanotubes in carbon counter electrode exhibit high catalytic activity for the reduction of triiodide to iodide and low charge transfer resistance at the electrolyte-electrode interface. The DSSC based on this counter electrode achieves a high power conversion efficiency of 6.94 % under 100 mW cm illumination (AM 1.5), which is comparable to 7.06 % for the DSSC with Pt counter electrode. It is expected that this low cost hybrid carbon counter electrode with simple manufacturing process would make the carbon catalyst-based monolithic DSSC more efficient in practical application. [ABSTRACT FROM AUTHOR]

Carbon black was embedded in mixtures of poly(ethylene oxide) and poly(vinylidene fluoride-hexafluoropropylene) to make a carbon/polymer composite slurry, which was deposited onto a transparent conducting glass substrate by a doctor-blade coating for application in dye-sensitized solar cells (DSSCs) as a counter-electrode (CE) material. The experiments indicated that the photovoltaic parameters of the DSSCs were strongly dependent on the carbon concentration in the slurry. The device with a carbon CE whose mass ratio was 1 : 1 (mass ratio = carbon black mass to polymer mass) exhibited an overall energy conversion efficiency of 4.62%; this was comparable to that of a device with platinum as a CE (5.32%) under the same test conditions. The better electrocatalytic activity of CE-1.0 (where 1.0 indicates the mass ratio of carbon black to polymer) for the reduction of triiodide resulted a higher performance of the DSSC with such a CE. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 [ABSTRACT FROM AUTHOR]

In this paper, nitrogen doped TiO2 photoanodes were achieved by calcining the mixture of urea and the commercial P25 nanoparticles slurry. Its application in the dye sensitized solar cells was examined. X-ray photoelectron spectroscopy indicated the N substituted the O atoms and formed N-Ti-O bonds. The optical band gap of the doped TiO2 photoanodes was reduced. From the photoelectrochemical experiments, it is known that nitrogen doping introduced new energy states above the valence band of the TiO2 photoanode, which lead to the visible light response and increased electron density. Optimized photo to electric conversion efficiency of the DSSC 6.71% is obtained with short current density (Jsc) of 14.3 mA cm-2, open circuit voltage (Voc) of 0.669 V and fill factor (FF) of 0.706 by the nitrogen doping, compared with 5.31% of the undoped one (Jsc of 13.2 mA cm-2, Voc of 0.638 V and FF of 0.624) at 0.99sun AM1.5, which is mainly due to the energy band structure change and partly the morphology change of the photoanode. [ABSTRACT FROM AUTHOR]

Sulfur-doped TiO2 is prepared by a mechanical process with ball milling the thiourea with commercial P25 TiO2 nanoparticles and successfully used as photoanode of dye-sensitized solar cells (DSSCs). The x-ray photoelectron spectroscopy results indicate that sulfur-doped TiO2 are locally distorted by incorporating S6+ species into TiO2 and substitutes for some of the lattice titanium (Ti4+); meanwhile, a clear reduction in the band gap energy of the sulfur-doped TiO2 photoanode compared to the band gap value for P25. The linear sweep voltammetry indicate that the edge of the conduction band of sulfur-doped TiO2 move positively toward the vacuum level. A conversion efficient of 6.91% was achieved for a DSSC based on sulfur-doped solar cell, which was 24% higher than that of the un-doped solar cell. The improved performance was ascribed to the improved charge injection from the dye to the sulfur doped TiO2 electrode, as evidence by an improved spectral response in the whole wavelength range. [ABSTRACT FROM AUTHOR]

Since carbon material was used as the electrode of perovskite solar cell (PSC), it has attracted wide attention because of its excellent thermal stability and low cost. However, serious charge recombination at the perovskite/carbon interface can lead to poor performance of carbon-based holeless PSCs. In this work, highly efficient and stable carbon-based PSC uses NiO nanoparticles as hole transport layer, which effectively promotes the separation and extraction of photogenerated carriers and inhibits the charge recombination at the perovskite layer/carbon electrode interface, thus improving the performance of the device. By optimizing the concentration of NiO nanoparticles, the power conversion efficiency (PCE) of carbon-based PSC reaches 13.6%. This work shows adding NiO nanoparticles between the perovskite film and the carbon electrode efficiently improve the hole extraction and the performance of PSC. [ABSTRACT FROM AUTHOR]

Abstract A uniform and compact hole blocking layer is necessary for high-performance perovskite solar cells, since it not only serves as an electron collector but also suppresses the carrier recombination. So far, high efficient perovskite solar cells have been obtained by using a blocking layer TiO 2 that requires an additional TiCl 4 treatment. In this paper, a comprehensive understanding of TiCl 4 treatment on the TiO 2 layer was investigated in planar perovskite solar cells. Scanning electron microscope, atomic force microscope, and Kelvin probe force microscopy were applied to investigate the morphology of the TiCl 4 treated TiO 2 , and steady-state photo luminescence spectroscopy and electrical impedance spectroscopy were conducted to study charge carrier dynamics. The TiCl 4 treated TiO 2 layer can result in high efficiency over 20% in planar perovskite solar cells. Our results demonstrate that the TiCl 4 treatment on the compact TiO 2 prior to the perovskite deposition was necessary for achieving high-performance solar cells. Graphical abstract Image 1 Highlights • TiCl 4 treatment on the TiO 2 layer was investigated comprehensively. • TiCl 4 treatment fills the cracks and pinholes of the TiO 2 layer. • TiCl 4 treatment depresses the surface work function of the TiO 2 layer. • Perovskite solar cells with the TiCl 4 treated TiO 2 result in high efficiency over 20%. [ABSTRACT FROM AUTHOR]

Highly transparent metal sulfides (Ni 3 S 4 , MoS 2 ) are directly deposited on fluorine doped tin oxide (FTO) substrates as effective Pt-free counter electrodes (CEs) for novel bifacial dye-sensitized solar cells (DSSCs). The blocky-like Ni 3 S 4 and petal-shaped MoS 2 nanoparticles (NPs) possess large surface area, which provides amount of active site to contact with electrolyte. The films not only show high transmittance at visible wavelengths, but also exhibit prominent electrocataltytic activity and outstanding metallic conductivity in iodine/iodide based bifacial DSSCs. Under front-side irradiation (100 mW/cm 2 ), the bifacial DSSC based on the transparent Ni 3 S 4 or MoS 2 CE presents remarkable photovoltaic conversion efficiency (E ff = 6.56%, 6.11%, respectively), closing to that of conventional Pt CE (E ff = 6.83%). Moreover, by appending an ordinary mirror as a photo reflector to achieve both-side illumination, the bifacial DSSC using the transparent Ni 3 S 4 or MoS 2 sample as CE obtained higher short-circuit current density (J sc ) and more attractive power conversion efficiency (PCE) (E ff = 7.06%, 6.65%, respectively). It indicates that the as-prepared transparent Ni 3 S 4 and MoS 2 CEs are promising potential candidates to explore low-cost and high-efficiency bifacial DSSCs. [ABSTRACT FROM AUTHOR]

Quasi-solid-state dye-sensitized solar cells (DSSCs) fabricated with the mixed-plasticizer (MP) modified polymer electrolyte are reported in this paper. The mixture of hydroxyethyl methylacrylate (HEMA) and ethylene glycol (EG) as plasticizer are added into the original composite polymer electrolyte (CPE) based on poly(ethylene oxide)/poly(vinylidene fluoride-hexafluoropropylene) (PEO/P(VDF-HFP)) and KI/I 2 . The olefinic bonds in HEMA and hydroxyl bonds in EG provide strong molecular polarity to effectively reduce the crystallinity of the polymer electrolyte, thus largely improve the ionic conductivity of the CPE. On account of MP, the decrease of crystallinity provides a better photovoltaic performance, the best photon-to-current conversion efficiency is 6.79% with a short current density J sc of 15.23 mA cm −2 under AM 1.5 illumination. Fourier transforms infrared (FT-IR), differential scanning calorimetry (DSC), ionic conductivity, electrochemical impedance spectroscopy are test to analyze superior property of DSSCs assembled with MP-modified CPEs. It shows that the performance of the CPEs can be largely improved by MP. [ABSTRACT FROM AUTHOR]

Abstract: Trap states play important role in electron transport of dye sensitized solar cells (DSSCs). Different trap states (surface and bulk traps) contribute differently to the performance of DSSCs. However, there is a lack of classification of the trap states, especially in recent doping works of the photoanodes. In this work, the Ce4+ (0.3, 0.6 and 0.9% molar ratio) in TiO2 and Ti4+ (15, 40 and 70% molar ratio) in SnO2 are assigned to surface traps and surface-and-bulk coexisted traps, respectively. The property of each trap state and its influence to the electron transport are characterized. Both the surface and bulk traps deteriorate the electron transport in DSSCs, however, the negative role of surface traps can easily be eliminated by surface modification in contrast to the bulk traps. Furthermore, contrary to the literature that the trap states will accelerate the interface recombination, it is found that the interface electron recombination time is prolonged with Ce4+ surface traps in TiO2 and Ti4+ bulk traps in SnO2, indicating that the recombination time is closely related to the property of the trap states. [Copyright &y& Elsevier]

Abstract: Quasi-solid-state dye-sensitized solar cells (DSSCs) are fabricated using tetraethylammonium tetrafluoroborate (Et4NBF4)-modified poly(ethylene oxide)/poly(vinylidene fluoride-hexafluoropropylene) (PEO/P(VDF-HFP)) composite polymer electrolytes (CPEs) along with KI and I2. Compared to the original CPE, the addition of Et4NBF4 mainly changes the conformation of the polymer structure, reduces the crystallinity of the polymer electrolyte specifically, and hence, increases the triiodide diffusion coefficient and the ionic conductivity, leading to the notable improved photovoltaic performance of DSSC. The DSSC based on the Et4NBF4 (0.15g)-modified CPE exhibits the best performance, with a short current density of 14.70mAcm−2 and a photoenergy conversion efficiency of 6.243% under an irradiance of 96.17mWcm−2. [Copyright &y& Elsevier]

Abstract: Ionic conductivity and the type of ions are important for the composite polymer electrolyte (CPE) of the dye-sensitized solar cells (DSSCs). Lithium bis(trifluoromethane sulphone)imide (LiTFSI for short) which is easy to dissociate, is added in the composite polymer electrolyte(CPE) as a plasticizer. The LiTFSI acts differently from the conventional LiClO4. LiTFSI changes the conformation of the polymer chain and shows higher ionic conductivity than LiClO4. That contributes to the improvement of the short current density of the DSSC. Furthermore, the DSSCs with LiTFSI modification show higher photovoltage than the LiClO4. The anions of TFSI− prohibit the interface recombination more effectively compared with the LiClO4 as the electrochemical impedance spectroscopy indicated. With the LiTFSI modified electrolyte, the performances of the DSSCs under 1 Sun, AM1.5 are improved and reaches the highest of 4.82% at the LiTFSI:LiI=0.116:1, much better than the original DSSC(3.6%) and the LiClO4 modified CPE electrolyte DSSC(4.32%). [Copyright &y& Elsevier]

Abstract: Quasi-solid-state dye-sensitized solar cells (DSSCs) are fabricated using acetamide-modified PEO/P(VDF-HFP) composite polymer electrolytes (CPEs) along with KI and I2. The DSSC assembled with acetamide-modified CPE shows higher open-circuit voltage and higher short-circuit photocurrent density than those of DSSC with unmodified CPE. With moderate acetamide content (0.20g) modification, the DSSC exhibits a 14.3mV improvement of photovoltage, a 2.83mAcm−2 improvement of current density and a improved performance of 6.04% compared with 4.68% of the original DSSC. Variations in the V oc and J sc are explained in terms of shift of the flat band potential of TiO2 and a complex formation between and –NH2 of acetamide in the electrolyte. [Copyright &y& Elsevier]

Abstract: A PEO/P(VDF-HFP) polymer-blend electrolyte is modified by different amounts of LiN(SO2CF3)2 (lithium bis(trifluoromethanesulfone)imide, LiTFSI). Fourier transform infrared (FT-IR) and differential scanning calorimetry (DSC) are carried out to examine the configuration changes of the polymer electrolyte. LiTFSI acts as a plasticizer influencing the ionic conductivity of the LiTFSI-modified polymer electrolyte, and improves the short-circuit photocurrent effectively. The electrochemical impedance spectroscopy (EIS) indicates that the intercalation or adsorption of overdose Li+ to the TiO2 photoanode surface positively changes the Fermi energy level and the conduction band. This improves the interface recombination in the DSSC and reduces the open-circuit voltage. With moderate LiTFSI content (0.05g, nKI/nI2 =7:1) modification, the DSSC exhibits a 1.6mAcm−2 improvement of current density and an improved performance of 5.03% compared with 4.51% of the original DSSC. [Copyright &y& Elsevier]

Abstract: Incorporating scattering centers in the nanocrystalline photoanode or additional scattering layers on the nanocrystalline photoanode is an effective way to enhance the light harvest efficiency (LHE) of the photoanode and the performance of dye-sensitized solar cells (DSSCs). In this work, mesoporous photoanodes were fabricated based on the composites of anatase TiO2 nanoparticles and carbon spheres. The holes were left after calcination thus serving as the light scattering centers in the photoanode. The size and the amounts of the holes were adjusted by changing the size (250, 500 and 700 nm) and concentration (5, 10, 15 and 20 wt% of the TiO2 nanocrystallines) of the carbon spheres in the slurry. The light scattering ability and the dye adsorption of the photoanodes with holes of varied size and contents were investigated. The holes left by calcinating the carbon spheres increased the light scattering of the photoanode. However, the increased light scattering ability offset the dye adsorption ability of the photoanode by high amounts of carbon spheres modification. The performances of the DSSCs are investigated under the simulated sunlight and the incident light (400–780 nm). The DSSC with photoanode made from the slurry with 500 nm and 15 wt% carbon spheres exhibited the opitimized performance (Jsc = 14.8 mA cm−2, Voc = 0.657 V, FF = 0.703 and η = 7.2%), much better than the DSSCs with photoanode made by the pure TiO2 nanocrystalline (Jsc = 11.7 mA cm−2, Voc = 0.645V, FF = 0.699 and η = 5.55%) and other photoanodes, indicating it best balanced the controversy of the enhanced light scattering ability and the decreased dye adsorption. The incident-photo-to-electric conversion efficiency test indicated the highest LHE of the 500 nm and 15 wt% carbon spheres modified photoanode. [Copyright &y& Elsevier]

Abstract: The anatase TiO2 hollow spheres with diameter of 500nm and shell thickness of 25nm are embedded in P25 TiO2 nanocrystalline photoanodes to improve the light scattering ability of the photoanode. Photoanodes embedded with different contents of TiO2 hollow spheres are prepared and the profiles of the photoanodes are systematically characterized. It is found that the morphologies of the photoanodes were modified by the TiO2 hollow spheres. With increasing the TiO2 hollow spheres’ contents, the light scattering ability of the modified photoanodes is effectively improved, while the dye adsorption decreases. By optimizing the TiO2 hollow spheres’ content in TiO2 nanocrystalline, a higher performance of the DSSC (J sc =16mAcm−2, V oc =0.72V, FF=0.648 and η =7.59%) is obtained compared with the pure TiO2 nanocrystalline DSSC (J sc =13.96mAcm−2, V oc =0.686V, FF=0.684 and η =6.67%, measured at 98.3mWcm−2, AM1.5). The improved performance is mainly due to the enhanced light scattering by the TiO2 hollow spheres. The open circuit voltage of the hollow spheres modified DSSCs is higher than that of the DSSC with pure P25 photoanode, which can be attributed to the fact that TiO2 hollow spheres substitute of the TiO2 nanocrystallines and reduce the interface recombination by decreasing the surface charge trap-site density of the photoanodes. [Copyright &y& Elsevier]

• Proline is added in PSCs, exhibiting PCE=19.6%. • Orientational crystallization was realized by steric hindrance effect. In perovskite solar cells, the molecule configuration of Lewis adducts closely related with its coordination ability, which needs careful design. In this work, two amino acids, circular proline and linear glycine are applied to reveal the steric effect of the Lewis-acid base additives. The proline with configuration and analogous size with Pb-Pb distance in perovskite crystals realizes better coordination effect, greatly promotes the perovskite crystal growth and trap states passivation. The PSCs with proline as additives in perovskite (PVK) exhibit the highest efficiency of 19.6% under 1 sun AM1.5, compared with 18.5% of PSC with glycine additive and 17.8% of the pristine PSCs. This work highlights steric effect should be considered when choosing and designing the Lewis adducts. [ABSTRACT FROM AUTHOR]

[Display omitted] • The coordination of S in TAA with Pb2+ is more effective than O in AA. • The high crystallinity and efficient defects passivation are realized with TAA. • The PSC based on TAA exhibits the highest performance of 15.87% and improved stabilty. In perovskite solar cells, the Lewis acid-base additives function effectively in high crystalline perovskite film formation and defects passivation. Exploration of effective Lewis acid-base additive to prepare high quality inorganic CsPbI 2 Br perovskite films with few defects is quite imperative. Here, thioacetamide with S-donor and acetamide with O-donor as Lewis base additives are investigated. It is revealed that a high electron density on S results in better coordination ability with Pb2+ in perovskite solution, leading to form high crystallinity film with lower defect states compared with O-donor. The inorganic CsPbI 2 Br based perovskite solar cells with thioacetamide additive exhibit the best performance of 15.87% (AM 1.5, 1 sun) and good ambient stability compared with the control device and device with acetamide. This work provides guidance for choosing and designing the effective additives for perovskite solar cells. [ABSTRACT FROM AUTHOR]

The stable CsPbBr 3 perovskite solar cell (PSC) has recently attracted wide attention, but its low photoelectric conversion efficiency is still the main concern at present. The quality of the perovskite absorber layer and the energy level matching between perovskite and hole transport layer (HTM) are important factors affecting the efficiency and stability of the PSCs. In this work, CsPbBr 3 film is prepared by multi-step solution spin coating method. In preparation process, a layer of BiBr 3 was modified on PbBr 2 film before the CsBr coating to form CsPbBr 3. This method can not only improve the crystal quality of perovskite, but also adjust the energy level to improve the carrier extraction. As the result, the photoelectric conversion efficiency (PCE) of carbon-based CsPbBr 3 PSCs has been effectively improved to 8.73%. This work demonstrates an effective approach to the preparation of high-quality perovskite films. • This work proposes a method of interface engineering used inorganic materials to improve photoelectric performance. • The photoelectric conversion efficiency of perovskite solar cells gets improved to 8.73%. • Efficient and very stable all-inorganic perovskite solar cells. • Inexpensive carbon electrode material. [ABSTRACT FROM AUTHOR]