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It is a great challenge to prepare high quality perovskite films in ambient atmosphere with high humidity (≥ 50%), since the commonly adopted two step sequential deposition process produces perovskite films with rough surfaces and a large amount of residual PbI 2 . To solve these problems, a facile method using combined solvent and vapor treatment is proposed. The residual PbI 2 is diminished through a solvent treatment process, and then smooth perovskite surface with micrometer scaled perovskite particles is obtained with a CH 3 NH 2 vapor treatment. The quality of the obtained perovskite films is examined in the hole transport material free perovskite solar cells, and power conversion efficiency is boosted up by 17.3% compared with the traditional method. When a CuPc hole transport layer is further introduced, carbon counter electrode based perovskite solar cells exhibit a superior power conversion efficiency of 16.61%. Thus this method shows great potential in further optimizing the performance of perovskite solar cells.

A facile approach to fabricate low-cost hole-transport-material (HTM)-free perovskite solar cell(PSC) based on commercial P25 nanoparticles and bilayer hybrid carbon electrode under ambient condition is reported. The performance of such HTM-free PSCs are highly dependent on the thickness and morphology of the P25 based TiO 2 electron-transport layer(ETL), which can be adjusted by the amount of ethanol and ethyl cellulose in the paste. After optimization, a power conversion efficiency of 12.48% is obtained, which is enhanced by 20.46% compared with solar cells employing hydrothermal TiO 2 ETL. In addition, PSCs with P25 ETL also exhibit excellent long-term stability together with reduced hysteresis. With advantages of low-cost, high efficiency and facile fabrication process, commercial P25 nanoparticles based PSC is highly potential for future commercialization.

Hierarchical TiO 2 spheres (HTS) containing needle–like nanorods and decorated with Au nanoparticles are synthesized, forming the HTS-Au microspheres. These microspheres are hybridized into TiO 2 nanocrystalline film to act as a scattering body on top of a pure TiO 2 nanocrystalline layer, forming a novel composite photoanode. The effects of such HTS-Au microspheres on the performance of the photoanode and dye-sensitized solar cell (DSSC) are studied. Study reveals that both light absorption and scattering in the photoanode are greatly enhanced, leading to the significant increases of the short-circuit current density (J sc ) and photoelectric conversion efficiency (η) of the DSSC. The optimal HTS-Au-based DSSC exhibits the maximum J sc of 14.56 ± 0.20 mA cm −2 and η of 7.37 ± 0.05%, markedly higher than those of the pure TiO 2 -NPs-based DSSC by 23.4% and 23.0%, respectively. The great improvements in the properties of the optimal HTS-Au-based DSSC can be mainly attributed to these factors: the heightened light absorption owing to the localized surface plasmon resonance from Au nanoparticles, the higher light scattering ability by the HTS microspheres, and the possible faster electron transfer channel provided by the needle-like nanorods. These different functions play important complementary roles in enhancing the light harvesting, the J sc and η of the DSSC.

A facile method is developed to prepare NiCo2S4 counter electrode (CE) which is in-situ grown on SnO2: F transparent conductive glass (FTO) with mirror-like smooth surface. As demonstrated by analyses, the electrocatalytic activity, electrical conductivity and light reflectivity of the NiCo2S4 CE exceed or approach to those of Pt-sputtering CE, and are much better than those of Pt-pyrolysis CE. Thus the conversion efficiency (η) of the dye sensitized solar cell (DSSC, 8.10%) based on NiCo2S4 CE is higher than the cell based on Pt-sputtering CE (7.60%), and is superior to the one based on Pt-pyrolysis CE (7.01%). Remarkably, NiCo2S4 CE also exhibits excellent chemical and mechanical stability. There are almost no changes on morphology and interfacial adhesion between NiCo2S4 film and FTO substrate after sequential 1000-time scans of cyclic voltammetry and 100 cycles of 3 M Scotch tape detachment. The η of DSSC drops a little from 8.10% to 7.94%. The numerous superiorities of the Pt-sputtering-like NiCo2S4 CE permit its promising application in DSSCs.

We have designed a novel hole-conductor-free and insulation layer free mesoscopic perovskite solar cells (PSCs) with a low cost carbon counter electrode (CE). Significantly, to enhance solar light harvesting capability, a mixture of methylammonium (CH3NH3+, MA) and formamidinium (HNCHNH3+, FA) cations were explored to synthesize superior performance perovskite materials. With the introduction of FAI, Cubic: Column composite structure of (FA)x(MA)1-xPbI3 was formed on the top of mesoscopic TiO2. This nanostructure not only leads to fully coverage of perovskite on TiO2 but also provides salutary electron transport channels to effectively reduce the electron recombination probability. As a result, optimal solar cell efficiency of 13.03% of (FA)x(MA)1-xPbI3 composite structure based PSC (when x is fixed at 0.25) was achieved, while PSC based typical MAPbI3 cuboids only obtained an efficiency of 12.49%. Despite of the improved efficiency, the Cubic: Column composite structure caused by the addition of FAI also contributes to higher long-term and thermal stability.

We synthesized highly uniform Au-decorated core-shell β -NaYF 4 :Er/Yb@SiO 2 microprisms and investigated its coupling effects on the performance of dye-sensitized solar cells (DSCs). The incorporation of upconversion phosphors (UCPs) and localized surface plasmon resonance (LSPR) arising from Au nanoparticles (AuNPs) was beneficial to achieve a higher photocurrent and power conversion efficiency of the devices. Furthermore, the contribution and interaction between upconversion and LSPR on the performance of DSCs were identified by UV–vis spectroscopy, upconversion fluorescence spectroscopy, and J - V characterization under different simulated illuminations. The presence of AuNPs increased the optical absorption of dye molecules in the visible region, but decreased the emission of UCPs. Thorough analysis showed that the energy of upconversion emission was transferred to the upconversion induced LSPR of AuNPs, that resulted from the incorporation between the SPR band of AuNPs and a matched emission bands of UCPs. These results validated the advantages of incorporation between upconversion and LSPR for DSC applications and revealed the underlying enhancement mechanism.

TiO 2 pyramids with planar-surface morphology presenting in the phases of anatase and brookite are successfully prepared, the height of which is 300-500 nm and 80-200 nm wide at the bottom. The pyramids exhibit excellent reflectance in the visible-near infrared region. When introducing the pyramids as a scattering layer covering the layer composed of TiO 2 nanoparticles, the energy conversion efficiency of dye-sensitized solar cell (DSSC) is enhanced from 6.49% to 7.25%. However, the pyramids overlayer falls from the nanoparticles underlayer easily, and the fill factor of the DSSC with the pyramids layer also become much lower. To solve the problem, we substitute TiO 2 microspheres underlayer for NP underlayer. As the tips of pyramids could be inserted into the submicron-sized gaps between the TiO 2 microspheres, the interface connection between layers of photoanode is reinforced. Current-Voltage measurement shows that the fill factor of the DSSC is much improved, and the DSSC has achieved 8.35% energy conversion efficiency. This study shows that the novel bilayer photoanode with improved light utilization and interface connection is an interesting structure for high efficiency DSSCs.

In this paper, we prepare a composite-hierarchical microsphere (HMS) which is composed of two kinds of HMSs: one flower-like microsphere (FMS, ∼1.5 μm, containing nanoparticles and nanowires) and plentiful mesoporous submicron ellipsoidal spheres (ESs, ∼200 nm, assembled with nanoparticles) which are embedded evenly in the FMS. For comparing, pure FMS and ES are prepared, respectively. It is found that the composite-HMS possesses (a) the highest BET surface area, (b) the highest light scattering ability, (c) the fastest electron transport and the longest electron life time, and (d) light trapping ability enabled by multiple light reflection and scattering between ESs and nanowires inside each FMS*ESs particle. The energy conversion efficiency of 7.91% of the DSSC based on FMS*ESs is higher than devices based on ES and FMS (7.22% and 7.24%, respectively), which also benefits from the structural advantages of the composite-HMS compared with non-composite HMSs.

Graphene quantum dots (GQDs) optimized TiO 2 photoanodes and their dye-sensitized solar cells (DSSCs) were successfully demonstrated in this study for the first time. The characteristics of GQDs were confirmed by Raman and TEM measurements. Study indicated that the amount of dye-adsorption decreased firstly and then increased as the increase of the GQDs in the photoanodes, while that the J sc , V oc and η of the corresponding DSSCs increased firstly and then decreased. Of all the DSSCs, the DSSC with an optimal amount of GQDs showed the best performance with a minimum dye-adsorption while the maximum J sc of 14.07 ± 0.02 mA cm −2 and η of 6.10 ± 0.01%, higher than those of the conventional DSSC (without GQDs) by 30.9% and 19.6%, respectively. The minimum dye-adsorption while the maximum J sc and η obtained in the optimal DSSC are mainly attributed to the unique photoexcitation response of GQDs and the hot electrons injection from GQDs into TiO 2 . This study indicates that not only the properties of DSSCs can be improved by GQDs, but more importantly, the reduced use of dye by using GQDs is of significant importance for the low cost and environment-friendly DSSCs.

In-doped TiO2 thin film was introduced at the interface of fluorine-doped tin oxide (FTO) substrate and mesoporous TiO2 film by spin-coating method, and its application as a new compact layer material for dye-sensitized solar cells (DSSCs) was investigated. The scanning electron microscopy (SEM), UV-visible spectroscopy, current-voltage characteristics, Mott-Schottky analysis, electrochemical impedance spectroscopy (EIS) analysis and open-circuit voltage decay (OCVD) technique are used to characterize the morphology, optical transmittance and flat-band potentials (Vfb) of In-doped titania compact film and its effect to the photoelectron conversion process. It was found that In-doping increased the transmittance of TiO2 compact layer, the interfacial resistance between FTO substrate and porous TiO2 film and the flat-band potential of TiO2 film. The In-doped TiO2 compact layer effectively suppressed the charge recombination from FTO to the electrolyte, increased the optical absorption of dye and then increased the short-circuit photocurrent density (Jsc). Furthermore, In-doped TiO2 compact layer acted as a weak energy barrier, which increased the electron density in the mesoporous TiO2 film, thus improved open-circuit photovoltage (Voc). As a result, the overall energy conversion efficiency of the DSSC with In-doped TiO2 compact layer was enhanced by 11.9% and 6.9% compared to the DSSC without compact layer and with pure TiO2 compact layer, respectively. It indicated that In-doped TiO2 is a promising compact layer material for dye-sensitized solar cells.

Light harvesting in dye-sensitized solar cells (DSSCs) mediated by plasmonic metallic nanoparticles and sub-micron light-scattering metal oxides is a facile and cost-effective approach to achieving high device performance. Ag nanoparticles, protected by thin shells of TiO2, were incorporated in TiO2 photoanode. The large plasmonic near-field intensity generated by these nanoparticles caused an 18.3% rise in photocurrent, which resulted in an enhanced efficiency of 6.23% as compared to 5.29% efficiency of DSSC based on unmodified TiO2 photoanode. In addition, DSSC with TiO2 nanofibers (NFs) embedded in TiO2 photoanode was also constructed, which because of the efficient light scattering ability of the nanofibers, attained an efficiency of 7.14% as a result of a current rise of 36.9%. Another DSSC was assembled with Ag NPs added to the photoanode of the NFs-based DSSC to further boost cell performance. The addition of Ag NPs, however, did not produce an appreciable change in the cell performance. The reason for this unexpected outcome was probably due to the low internal resistance associated with charge recombination and large resistance to electron transport in the cell as determined by electrochemical impedance analysis computed in this work.

A facile and reliable method is applied to prepare the electrolyte based on hydroquinone (HQ)/benzoquinone (BQ) redox couple for dye-sensitized solar cells (DSSCs) in open environment by adding moderate amount of acetic acid (HAc), and the best conversion efficiency (η) of 5.82% is achieved under 100 mW cm−2 (AM 1.5 G) illumination. Electrochemistry properties of DSSCs using such redox couple are measured and the results show a higher current and better charge transfer in contrast to I−/I3−. And a slightly higher efficiency of 5.88% is obtained when HQ and BQ are symmetrically substituted by two methyls. With advantages of high efficiency, compatible with the most common dye N719 and easily tuned by facile structural modification, the redox shuttle employing HQ/BQ via HAc treatment is very promising to be employed in efficient DSSCs.

TiO 2 doping has been widely used to improve the performance of dye-sensitized solar cells. In this paper, we study the use of N as a dopant of TiO 2 in dye-sensitized solar cells (DSSCs), analyzing the effect on the photovoltaic properties of the cells based on different amounts of N doping. Results indicate that the dye absorption is increased, which would enhance the amount of photoelectron; moreover, the resistance ( R 3 ) of the electron transport within photoelectrode and electron lifetime of it are improved by N doping. The above two reasons would lead the high short circuit current density ( J sc ). However, owing to the sites of recombination and severe defects introduced, the trend of dye absorption, R 3 and electron lifetime is opposite when the amount of N doping is more than 3%. Finally, we find that the optimal amount of N doing is 3%, which outstandingly increase the performance of DSSCs. The conversion efficiency of the DSSCs can be reached to 6.25% when using the 3% N-doped TiO 2 photoelectrode, and this efficiency is 23.03% higher than that of the pure TiO 2 .

A series of dye-sensitized solar cells (DSSCs) with different graphene-P25 (G-P25) photoelectrodes were prepared by a ball milling method. The influences of graphene on the structures and performance of G-P25 cells were studied. Studies indicated that the rutile contents in G-P25 photoelectrodes increased with increasing graphene-oxide (GO) additions and reached the maximum value at GO addition of 4.5 ml. And with the increase of GO additions, the porosity of the G-P25 photoelectrodes, the interface recombination resistances, and the short current densities increased. When the GO addition was 4.5 ml, the G-P25 cells showed the best performance with the largest interface recombination resistance of 15.12 Ω and the largest photoelectric conversion efficiency of 5.09%, which was remarkably higher than those of pure P25 DSSC. Since the tendency of the photoelectric conversion efficiency varying with the GO additions was in consistence with that of the rutile contents, the enhancement of the photoelectric conversion properties of the G-P25 DSSCs was preliminary attributed to the increase of the rutile contents and the porosity in the photoelectrodes due to graphene adding.

This paper reports an inverted fabrication process for the photoanode of a flexible dye sensitized solar cell (DSSC). This procedure involves assembling a free-standing TiO2 nanowires/nanoparticles hybrid membrane, via high temperature annealing, sputtering an indium tin oxide (ITO) layer onto this membrane, and transferring these onto a polydimethylsiloxane (PDMS) substrate. The inverted procedure prevents thermal decomposition of polymer substrate, whilst enabling effective thermal treatment of the functionalized titanium oxide. The flexible DSSC fabricated in this way has an efficiency of 2.7%, which is comparable with rigid device constructed using similar materials.

This study describes a systematic investigation of the stability of a carbon/TiO 2 counter electrode for use in dye-sensitized solar cells (DSSCs). In this system, nanoparticle additives were introduced by adding Ti-hydrogel. The additives then bound carbon particles and enhanced the adhesion of carbon materials to the conductive substrate. After introducing the Ti-hydrogel into the carbon paste, the carbon/Ti-hydrogel composited counter electrode (HC-CE) showed a better conductivity and stability compared with that of the carbon counter electrode (C-CE), while the catalytic activity was not influenced. The device based on the HC-CE showed superior power conversion efficiency (6.3%) and long-term stability over the device based on the C-CE (5.8%).

TiO2 sols were synthesized via hydrothermal reaction using a less hydrolysable alkoxide or tetrabutyl titanate as the starting material. Using characterizations of X-ray diffraction, dynamic laser scattering and transmission electron microscopy, particle coarsening dynamics along with the particle dispersion behavior in the sols were studied via changing hydrothermal temperature from 160 °C to 250 °C. It was observed that, pure anatase phase was obtained in the whole examined temperature range. With temperature increasing, the particle size distribution in the sols first narrowed, and then broadened. Mono-dispersed nanocrystallites were obtained at the temperature of 220 °C. Aggregations were formed between the nanocrystallites at other temperatures. The causes of the aggregating behavior were analyzed and found to be different when the temperature was less than or beyond 220 °C. The as-synthesized TiO2 sols were used in fabrication of dye sensitized nanocrystallite solar cell. The cells assembled from temperature of 220 °C came out with the best photo-to-electric energy conversion efficiency, which is ascribed to the improved dispersion of particles in TiO2 sols.

Counterelectrode plays an important role in dye sensitized solar cells. It helps the regeneration of the redox couples in electrolyte and makes the cell a complete circuit. In order to improve the electrochemical performance of counterelectrode, a strategy of sandblasting has been utilized to pre-treat the surface of glass substrate. Counterelectrodes were fabricated by sputtering Pt/Ti bilayers films onto the treated substrates. Morphological, electrical, electrochemical and optical properties of the counterelectrode were characterized by scanning electronic microscopy, four-probe measurement, electrochemical impedance spectroscopy, cyclic voltammetry and UV–vis reflection spectroscopy, respectively. Effect of the treatment on these properties was evaluated. It was found that counterelectrode made from sandblasted substrates showed increased roughness of surface and sheet resistance, along with the enhanced catalysis efficiency and improved light scattering. The enhanced catalysis efficiency toward reduction of tri-iodide was found to be due to smaller Pt crystallite grown on the sandblasted substrate, since the electrochemical active surface area changed little. And scattering was caused by increased roughness of the substrate. Typical solar cells were assembled with the counterelectrode made of the sandblasted substrates. Effect of the treatment on current–voltage curves and performance parameters of the solar cells was checked and discussed.

A PEO/P(VDF-HFP) composite polymer electrolyte was modified by different amounts of NH 2 -end functional silane (3-amonopropyltriethoxysilane, APTS). Fourier transform infrared (FT-IR), X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were carried out to examine the configuration changes of the polymer electrolyte. The newly formed Si–O–Si network and interactions influenced the ionic conductivity of the APTS-modified polymer electrolyte and also enhanced the connection of the polymer electrolyte with the electrodes of the dye sensitized solar cells (DSSCs). The cyclic voltammograms and electrochemical impedance measurements indicated that the APTS deprotonated the TiO 2 photoanode surface and negatively changed the Fermi energy level and the conduction band edge to the vacuum level. This effectively reduced the interface recombination in the DSSC and improved the open circuit voltage. With moderate APTS content (0.1 M) modification, the DSSC exhibited a 58 mV improvement of photovoltage and an improved performance of 5.08% compared with 3.74% of the original DSSC.