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The defects at the interface and grain boundaries of perovskite films downgrade the performance of perovskite solar cells (PSCs) dramatically. Hence, improving perovskite film quality is essential for the achievement of high-performance solar cells. Herein, three new dicyclopentadithienothiophene (DCDTT)-based non-fullerene acceptors (NFAs) IN-DCDTT (1), INCl-DCDTT (2), and INBr-DCDTT (3) are developed as a promising platform for organic–inorganic hybrid perovskite solar cells to achieve simple preparation, high efficiency, and good stability. SEM and XRD data indicate that, with the addition of chlorinated NFA 2 in the active layer preparation, perovskite hybrid films exhibit larger grain sizes and higher crystallinity than pristine perovskite films. As shown by EDS and IR, all the non-fullerene acceptors (compounds 1–3) with functional carbonyl (C＝O) and cyano (C≡N) groups have good interaction with undercoordinated Pb atoms and passivate the trap states in the perovskite films. Time-resolved photoluminescence reveals that the molecule INCl-DCDTT (2) facilitates efficient hole extraction. Consequently, solar cells based on 2−perovskite hybrid films yield an excellent power conversion efficiency of 21.39% with an FF of 0.82, a Jsc of 23.71 mA cm−2, and a Voc of 1.10 V, which represents a significant improvement as compared to a PCE of 17% obtained for the control device. Meanwhile, devices based on IN-DCDTT (1) and INBr-DCDTT (3)−perovskite hybrid films also show enhanced performance with a slightly lower PCE of 19.21% and 20.59%, respectively than cells based on 2−perovskite hybrid films. The cost-effective chlorinated INCl-DCDTT (2) and brominated INBr-DCDTT (3) organic small molecules were successfully used as donor passivation agents to improve the photovoltaic performance of Pb-based PSCs. Furthermore, compound 1–3 derived PSC devices also exhibit excellent long-term stability enhancement. In particular, a device based on INCl-DCDTT (2) treated perovskite retains ∼90% of the initial PCE after 63 days in a glove box as compared to that (55%) of the control device. This simple surface treatment, by the addition of new NFAs, provides a new strategy to simultaneously passivate surface defects and enhance charge transport at the device interface. [ABSTRACT FROM AUTHOR]

A new inorganic hole transporting layer, a sputtering made LiCoO2 film, was developed and used in an inverted perovskite solar cell (PSC) and sub-module (PSM). The LiCoO2 film prepared by RF magnetron sputtering is composed of nano-sized particles and a superhydrophilic surface after treating it with UV–ozone, and therefore can be wetted evenly with a (MAI + PbI2)/(DMF + DMSO) precursor solution. By applying chlorobenzene as an anti-solvent, a very dense film with big perovskite grains was formed. After depositing the C60 electron transporting layer, BCP hole blocking layer and Ag electrode, the best perovskite solar cell achieves a power conversion efficiency (PCE) of 19% with negligible current hysteresis. The high-efficiency cell is stable up to 90 °C in the inert atmosphere without encapsulation, and the PCE only decreases by 2% when the cell was heated at 100 °C for 30 minutes. When the cell was heated at 100 °C for 5 days, the PCE decreases by only 40%; nevertheless, under the same heating conditions, the efficiency of the PSC based on the PEDOT:PSS HTL is lost totally. The superhydrophilic surface of LiCoO2 made the even wetting of the large surface area with the perovskite precursor solution possible. Therefore the perovskite solar sub-module with an active area of 25.2 cm2 (on a 10 cm × 10 cm substrate) can be fabricated to achieve a power conversion efficiency of 16% which was further verified to be 15%. The high-efficiency sub-module based on the LiCoO2 HTL also shows good thermal stability, and ca. 10% of the efficiency was lost by heating at 100 °C for 30 minutes. The development of new inorganic hole transporting layers for large area, thermally stable and highly efficient perovskite solar sub-modules closes the gap for their near-future market exploitation. [ABSTRACT FROM AUTHOR]

Four heterocyclic spiro-type hole transporting materials (HTMs) carrying a spiro[fluorene-9,9′-xanthene] (SFX) (SFX-TPAM and SFX-TPA) or spiro[fluorene-9,9′-thioxanthene] (SFT) unit (SFT-TPAM and SFT-TPA) were synthesized through a low-cost facile route with high yields for perovskite solar cell (PSC) applications. In terms of absorption, these four compounds in the film state are all transparent at wavelengths longer than 430 nm, which is beneficial for allowing visible light to reach the perovskite active layer without being absorbed by the hole transporting layer (HTL). The photovoltaic performance of the inverted PSCs based on these small molecular HTMs with the device architecture of glass/ITO/HTL/CH3NH3PbI3/C60/BCP/Ag was tested. Only SFX-TPAM had its highest occupied molecular orbital (HOMO) level matched with the valence band of CH3NH3PbI3. The inverted PSC based on a dopant-free SFX-TPAM HTL achieves a power conversion efficiency of 10.23% under the illumination of standard one sun lighting, which is better than that (8.17%) of the cell based on dopant-free spiro-OMeTAD. The better photovoltaic performance of SFX-TPAM compared to spiro-OMeTAD may be due to the MAPbI3 film deposited on it having better quality. These results indicate that the facilely synthesized, low-cost SFX based small molecules can be used as the HTMs for PSCs. [ABSTRACT FROM AUTHOR]

Anatase titanium dioxide (an-TiO2) is often used as the electron transporting material (ETM) in planar-heterojunction perovskite solar cells (PSCs) because of its excellent semiconductor characteristics, outstanding optical transmittance, and suitable band structure. Herein, we report an inexpensive method for mass-scale production of TiO2 ETMs at room temperature (RT ∼ 30 °C), involving the grinding of large clumps of an-TiO2 to form a suspension of TiO2 nanoparticles (NPs) in isopropyl alcohol for meso-superstructured PSCs. This process does not involve any chemical synthesis; it is a purely physical process. The lowest unoccupied molecular orbital (LUMO) of ground an-TiO2 NPs, estimated using ultraviolet photoelectron spectroscopy (UPS), was ca. 4.06 eV, which is a salient feature for the active layer. A regular perovskite solar cell (PSC) based on a CH3NH3PbI3 absorber and ground an-TiO2 ETL exhibited a champion power conversion efficiency (PCE) of 17.43% with an active area of 0.1 cm2. The same ground an-TiO2 NPs were used to fabricate a large-area (designated area: 25.2 cm2) PSC and a PCE of 14.19% was achieved. PSC devices incorporating the ground an-TiO2 NP ETLs exhibited an attractive long-term device stability, with the PCE retaining approximately 85% of the initial values after 80 days. [ABSTRACT FROM AUTHOR]

A new series of metal-free alkylated tetrathienoacene (TTAR)-based organic chromophores, TPA–TTAR–TA (R = branched-C8H17, 1, TTAR-b8; R = C15H31, 2, TTAR-15; R = C9H19, 3, TTAR-9), are synthesized for application in dye-sensitized solar cells (DSSCs). Due to the extensively conjugated TTAR π-bridge, all three dyes exhibit high extinction coefficients (1 × 105 M−1 cm−1). By systematically exploring the effects of the TTAR alkyl chain substituents, a significant influence of the dye coverage (orientation) on the TiO2 surfaces is observed. The branched-alkyl TTAR-b8 (1) promotes significant tilting and packing distortion on TiO2 in comparison to more ordered monolayers of linear long alkyls TTAR-15 (2) and TTAR-9 (3). Photophysical measurements on the dye-grafted TiO2 films reveal that the branched-alkylated TTA unit in 1 enhances the electron injection efficiency, in agreement with the high quantum efficiency. Notably, by utilizing a three-dimensional (3D) photonic crystal (PhC) layer to enhance the coherent scattering an increase the light absorption, TTAR-b8 exhibits higher short-circuit current densities and achieved a high PCE of 11.18%. TTAR-b8 is thus the best performing fused-thiophene-based organic DSSC dye reported to date. [ABSTRACT FROM AUTHOR]

An organic lead halide perovskite film proved to be an excellent light harvesting material for solar cells. The ability to prepare high quality perovskite films, with large areas, for solar modules using simple methods is essential for commercializing this promising photovoltaic technology. By combining the composition of the halogens (Cl can improve the morphology of the film by reducing the crystallization rate, and Br can increase the Voc and stabilize the crystal lattice) and film casting engineering (hot solution spin-coating (HSS) and solvent annealing (SA)), high quality single-phase mixed-halide perovskite films can be prepared using a one-step method. This new method can not only prepare high quality, small area films reproducibly but also be adopted readily to prepare high quality homogeneous films with large areas for perovskite solar modules. An inverted mixed-halide perovskite solar module (active area of 25.2 cm2) achieves the highest efficiency of 14.3% with a remarkably high FF of 74.4% and has no current hysteresis. [ABSTRACT FROM AUTHOR]

Replacing toxic halogenated solvents with eco-friendly solvents will be necessary for the upscaling and mass production of organic photovoltaics (OPVs). In this study, toluene (Tol), a halogen-free solvent, was employed in the fabrication of molecular solar cells, achieving a power conversion efficiency (PCE) higher than that obtained when using a chlorinated counterpart, chloroform (CF). SMPV1, a two-dimensional conjugated small molecule, was used as the donor and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as the acceptor to form bulk heterojunction (BHJ) OPVs. The as-cast device formed using Tol displayed a PCE of 5.4%, higher than that (4.8%) achieved using CF. Combining the effects of thermal annealing and polydimethylsiloxane (PDMS) as a solvent additive, the PCEs of devices prepared using Tol and CF reached 6.20 and 5.52%, respectively. Solvent vapor annealing (SVA), a powerful tool for controlling the morphology of the active layer, had a great impact on the device performance. Tol, tetrahydrofuran (THF), carbon disulphide (CS2), and hexane (Hex) were tested as halogen-free solvents for SVA treatment. Tol- and THF-SVA had positive effects on PCEs, reaching 7.04 and 6.50%, respectively. The enhancement arose mainly from the improvement in the fill factor, due to morphological manipulation and favorable phase separation. CS2- and Hex-SVA treatment had negative effects on the short-circuit current density and, hence, the overall PCE. A PCE of greater than 7% is the highest performance reported to date when using a halogen-free solvent to prepare small-molecule solar cells. [ABSTRACT FROM AUTHOR]

Ternary bulk heterojunctions (BHJs) are platforms that can improve the power conversion efficiencies of organic solar cells. In this paper, we report an all-small-molecule ternary BHJ solar cell incorporating [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) and indene-C60 bisadduct (ICBA) as mixed acceptors and the conjugated small molecule (2Z,2′E)-dioctyl 3,3′-(5′′,5′′′′′-(4,8-bis(5-octylthiophen-2-yl)benzo[1,2-b:5,4-b′]dithiophene-2,6-diyl)bis(3,4′,4′′-trioctyl-[2,2′:5′,2′′-terthiophene]-5′′,5-diyl))bis(2-cyanoacrylate) (BDT6T) as a donor. When incorporating a 15% content of ICBA relative to PC71BM, the ternary BHJ solar cell reached a power conversion efficiency of 6.36% with a short-circuit current density (JSC) of 12.00 mA cm−2, an open-circuit voltage (VOC) of 0.93 V, and a fill factor of 0.57. The enhancement in efficiency, relative to that of the binary system, resulted mainly from the increased value of JSC, attributable to not only the better intermixing of the donor and acceptor that improved charge transfer but also the more suitable morphology for efficient dissociation of excitons and more effective charge extraction. Our results suggest that there is great potential for exceeding the efficiencies of binary solar cells by adding a third component, without sacrificing the simplicity of the fabrication process. [ABSTRACT FROM AUTHOR]

It has been a concern that the cobalt redox cannot give a good performance for the dye-sensitized solar cells when it is used with ruthenium dyes. The electron dynamics measurements clarified the electron loss processes, and clarified the cause. The result indicated the direct interaction between the ruthenium dyes with the cobalt redox, and it reduced the charge injection from the triplet state of the dyes to the titanium oxide, and also it increased the electron recombination process with the cobalt redox species. Both the problems of injection and recombination were solved by using the ruthenium dye with alkyl chains keeping a distance between the dye and the cobalt redox. [ABSTRACT FROM AUTHOR]

Two heteroleptic ruthenium complexes, SJW-B18 and CYC-B11H, with four alkyl groups and two alkyl groups, respectively, on the terminal of their ancillary ligand were prepared. These two complexes have a similar absorption profile, energy level and orbital distribution of the frontier orbitals. Therefore, they are good model compounds to explore the effect of the molecular structure of a ruthenium sensitizer on their photovoltaic performance, especially when cobalt electrolyte was used in assembling the device. When I-/I3- electrolyte was employed, the dye-sensitized solar cell based on SJW-B18 and CYC-B11H sensitizers achieved similar power conversion efficiencies of 9.54% and 9.64%, respectively, because the two dyes have similar optical and electronic properties. Nevertheless, when Co(II)(III) electrolyte was used, the SJW-B18 sensitized device has a higher efficiency (7.30%) than the CYC-B11H-based cell (6.65%), mainly in higher open-circuit voltage (0.829 V vs. 0.784 V). Electrochemical impedance and intensity modulated photocurrent/photovoltage spectroscopic data reveal that the SJW-B18 dyed titanium dioxide (TiO2) anode has better surface protection compared to the CYC-B11H adsorbed TiO2 film. The physical insulation of the TiO2 surface with the four alkyl groups on the SJW-B18 dye can reduce the charge recombination between the electron on TiO2 and Co(III) to increase the open circuit voltage, and the power conversion efficiency of the device. These results provide a new strategy for designing ruthenium sensitizers which are compatible with a cobalt-based electrolyte. [ABSTRACT FROM AUTHOR]

A two-step, spin-coating process to synthesize a high quality perovskite film at room temperature at ambient atmosphere is reported. Combining an optimized PEDOT:PSS hole-transport layer and a PC71BM acceptor, the device achieved a power conversion efficiency of 16.31% with a remarkably high Voc of 1.05 V and FF of 0.78. The efficiency reproducibility of the devices is also high: 80% of devices achieve efficiency higher than 15%. [ABSTRACT FROM AUTHOR]

Fast electron transport, large specific surface area, and slow interfacial electron recombination are indispensable features for efficient photoelectrodes of dye-sensitized solar cells (DSSCs). Highly ordered TiO[sub 2] nanotubes (TNT) with advanced architecture of high surface-to-volume ratio and open-up geometry for providing direct electron/ion transport channels is applied on a flexible photoanode in this study. Because several micrometers of semiconductor are required for the diffusion of electrons, which are surrounded by electron acceptors at a distance of only several nanometers, a wide band gap barrier layer of Y[sub 2]O[sub 3] is coated on TNT to retard back-transfer of electrons to the electrolyte or to the oxidized dye molecules by electrodepositing Y(OH)[sub 3] on the TNT surfaces and subsequently annealing the samples. By adjusting the charge capacity for Y(OH)[sub 3] electrodeposition, the charge recombination dynamics in the pertinent DSSC can be easily controlled. This barrier layer also enhances dye adsorption and therefore increases the volume of the optically active component due to the more basic surface of Y[sub 2]O[sub 3] for more carboxyl groups in a dye molecule adsorbing onto the surface. A higher light-to-power conversion efficiency (h) of 6.52% is obtained for the pertinent DSSC compared with a reference cell with non-coated TNT (h = 5.35%), exhibiting an enhancement of 22% in h. [ABSTRACT FROM AUTHOR]

A new ruthenium photosensitizer, coded CYC-B7, incorporating a bithienyl-carbazole antenna ligand was designed and prepared for improving the open-circuit voltage (Voc) of a dye-sensitized solar cell (DSC) device. This new sensitizer displays the low energy MLCT transition band centered at 551 nm with a high molar absorption coefficient of 2.19 × 104M−1cm−1. In addition, a simple approach to reduce the aggregation of bulky ruthenium dyes assembled onto the surface of TiO2film is demonstrated. The cell based on this new heteroleptic ruthenium dye provides a high Vocof 788 mV and an overall conversion efficiency (η) of 8.96%. The functionality of carbazole in CYC-B7resulting in the increases of the Vocvalue of the corresponding device is verified by comparing with the performance of the DSC sensitized with a structurally similar dye without carbazole. [ABSTRACT FROM AUTHOR]

Three types of flexible dye-sensitized solar cells (DSSC) were fabricated, using as the photoanode an array of TiO2nanotubes (TNT) or TiO2nanotubes filled with TiO2nanoparticles (TNT-TNP, particle size 14 nm) or TiO2nanotubes not only filled with nanoparticles but also coated with a layer of strontium oxide (TNT-TNP-SrO). The nanotubes were obtained by electrochemical oxidation of a Ti sheet and their lengths (0.5 μm to 18.8 μm) were controlled by varying the anodization period from 0.25 to 18 h. The DSSC using titanium nanotube arrays as the photoanode (hereafter called TNT-DSSC) showed a solar-to-electricity conversion efficiency (η) of 3.46%, when the anodization period was 12 h. When TNT-TNP was used as the anode, the efficiency of the DSSC (hereafter called TNT-TNP-DSSC) has increased to 4.56%. An efficiency of 5.39% was obtained when TNT-TNP-SrO was used as the photoanode for the DSSC (hereafter called TNT-TNP-SrO-DSSC). Our own dye, coded as CYC-B1 was used in all the cases. The morphologies of TNT and TNT-TNP were characterized by FE-SEM. XRD was used to characterize the TNT. Explanations on the photovoltaic performances of the DSSCs are substantiated by using electrochemical impedance spectra (EIS), incident photon to current conversion efficiency (IPCE) curves, and Mott-Schottky plots. [ABSTRACT FROM AUTHOR]

Three types of flexible dye-sensitized solar cells (DSSC) were fabricated, using as the photoanode an array of TiO2nanotubes (TNT) or TiO2nanotubes filled with TiO2nanoparticles (TNT-TNP, particle size 14 nm) or TiO2nanotubes not only filled with nanoparticles but also coated with a layer of strontium oxide (TNT-TNP-SrO). The nanotubes were obtained by electrochemical oxidation of a Ti sheet and their lengths (0.5 μm to 18.8 μm) were controlled by varying the anodization period from 0.25 to 18 h. The DSSC using titanium nanotube arrays as the photoanode (hereafter called TNT-DSSC) showed a solar-to-electricity conversion efficiency (η) of 3.46%, when the anodization period was 12 h. When TNT-TNP was used as the anode, the efficiency of the DSSC (hereafter called TNT-TNP-DSSC) has increased to 4.56%. An efficiency of 5.39% was obtained when TNT-TNP-SrO was used as the photoanode for the DSSC (hereafter called TNT-TNP-SrO-DSSC). Our own dye, coded as CYC-B1 was used in all the cases. The morphologies of TNT and TNT-TNP were characterized by FE-SEM. XRD was used to characterize the TNT. Explanations on the photovoltaic performances of the DSSCs are substantiated by using electrochemical impedance spectra (EIS), incident photon to current conversion efficiency (IPCE) curves, and Mott-Schottky plots. [ABSTRACT FROM AUTHOR]

A high light-harvesting ability heteroleptic ruthenium complex dye, SJW-E1, was examined as a sensitizer for the plastic dye-sensitized solar cells (DSSCs) constructed by a low-temperature electrode preparation method using binder-free TiO2paste and an ITO-PEN substrate. The effects of a TiOxbuffer layer, electrolyte composition and co-adsorbents on the cell performance as well as the cell long-term stability were investigated. The TiOxbuffer layer has not only enhanced the adhesion between TiO2thin film and the ITO/PEN substrate but also reduced the electron recombination, resulting in the improvement of the fill factor (FF) and therefore the photovoltaic performance of the solar cells. The optimized solar cell based on SJW-E1dye showed an efficiency of 6.31%. Furthermore, the plastic DSSCs based on the SJW-E1dye shows a better cell stability compared to that based on N719dye after a full sunlight soaking (at ca.50 °C) for 500 h. These results demonstrated that the flexible DSSCs based on the high light-harvesting, well-functionalized heteroleptic ruthenium dye could achieve both high performance and good stability. [ABSTRACT FROM AUTHOR]

Poly(acrylonitrile-co-vinyl acetate) (PAN-VA) is utilized as a gelation agent to prepare gel-state electrolytes for dye-sensitized solar cell (DSSC) applications. Based on the synergistic effect of PAN-VA and TiO(2) fillers in the electrolyte, the gel-state DSSC can achieve a conversion efficiency higher than that of a liquid counterpart. The high performance of the gel-electrolyte is attributed to the in situ gelation property of the gel-electrolyte, the contribution of the PAN-VA to the charge transfer, as well as the enhancement effect of TiO(2) fillers on the charge transfer at the Pt-electrolyte interface. The experimental results show that the efficiencies of the gel-state cells have little dependence on the conductivity of the electrolytes with various contents of PAN-VA, but are closely related to the penetration situation of the electrolyte in the TiO(2) film. For PAN-VA concentrations ≤15 wt%, the electrolyte can be easily injected at room temperature based on its in situ gelation property. For higher PAN-VA concentrations, good penetration of the high viscous electrolyte can be achieved by elevating the operation temperature. By utilizing a heteroleptic ruthenium dye (coded CYC-B11), gel-state DSSCs with an efficiency of above 10% are obtained. Acceleration tests show that the cell is stable under one-sun illumination at 60 °C.

Quantum dot-sensitized solar cells (QDSCs) constructed using cascade CdS/CdSe sensitizers and the novel tetrapod-like ZnO nanoparticles have been fabricated. The cascade co-sensitized QDSCs manifested good electron transfer dynamics and overall power conversion efficiency, compared to single CdS- or CdSe-sensitized cells. The preliminary CdS layer is not only energetically favorable to electron transfer but behaves as a passivation layer to diminish the formation of interfacial defects during CdSe synthesis. On the other hand, the anisotropic tetrapod-like ZnO nanoparticles, with a high electron diffusion coefficient, can afford a better carrier transport than traditional ZnO nanoparticles. The resultant solar cell yielded an excellent performance with a solar power conversion efficiency of 4.24% under simulated one sun (AM1.5G, 100 mW cm(-2)) illumination.

Friction Nanolithography (FRNL) is used to fabricate polyaniline nano-wire on a flexible, insulating, and highly transparent substrate. FRNL uses SPM tip to scratch the substrate to form a trench with higher friction force. Polyaniline nano-wire is selectively deposited on the trench. Sub-100 nm polyaniline wire is fabricated based on FRNL.