Dopant-Free Hole-Transporting Materials for Stable and Efficient Perovskite Solar Cells.

Molecularly engineered novel dopant-free hole-transporting materials for perovskite solar cells (PSCs) combined with mixed-perovskite (FAPbI3 )0.85 (MAPbBr3 )0.15 (MA: CH3 NH3+ , FA: NH=CHNH3+ ) that exhibit an excellent power conversion efficiency of 18.9% under AM 1.5 conditions are investigated. The mobilities of FA-CN, and TPA-CN are determined to be 1.2 × 10-4 cm2 V-1 s-1 and 1.1 × 10-4 cm2 V-1 s-1 , respectively. Exceptional stability up to 500 h is measured with the PSC based on FA-CN. Additionally, it is found that the maximum power output collected after 1300 h remained 65% of its initial value. This opens up new avenue for efficient and stable PSCs exploring new materials as alternatives to Spiro-OMeTAD.

A dual-functional asymmetric squaraine-based low band gap hole transporting material for efficient perovskite solar cells.

We demonstrate for the first time an asymmetric squaraine-based low band-gap hole transporting material, which acted as both light harvesting and hole transporting layers in methylammonium lead triiodide perovskite solar cells. Opto-electrochemical characterization revealed extremely high molar extinction coefficients of the absorption bands in the low energy region and prominent space charge delocalization due to its electronically asymmetric nature. A suitable band alignment of the squaraine HOMO level with the valence band edge of the perovskite, and the conduction band of the TiO2 with LUMO of the perovskite allowed a cascade of hole extraction and electron injection, respectively. Red-shifted absorption was observed for both HTMs in thin films coated on the perovskite, and the optimized devices exhibited an impressive PCE of 14.7% under full sunlight illumination (100 mW cm(-2), AM1.5 G). The efficiency value is comparable to that of the devices using a state-of-the-art spiro-OMeTAD hole transport layer under similar conditions. Ambient stability after 300 h revealed that 88% of the initial efficiency remained for , and almost no change for , indicating that the devices had good long-term stability thus suggesting that the asymmetric squaraines have great potential as a dual-functional HTM for high performance perovskite solar cells.

Efficient Hole-Transporting Materials with Triazole Core for High-Efficiency Perovskite Solar Cells.

Efficient hole-transporting materials (HTMs), TAZ-[MeOTPA]2 and TAZ-[MeOTPATh]2 incorporating two electron-rich diphenylamino side arms, through direct linkage or thiophen bridges, respectively, on the C3- and C5-positions of a 4-phenyl-1,2,4-triazole core were synthesized. These synthetic HTMs with donor-acceptor type molecular structures exhibited effective intramolecular charge transfer for improving the hole-transporting properties. The structural modification of HTMs by thiophene bridging might increase intermolecular π-π stacking in the solid state and afford a better spectral response because of their increased π-conjugation length. Perovskite-based cells using TAZ-[MeOTPA]2 and TAZ-[MeOTPATh]2 as HTMs afforded high power conversion efficiencies of 10.9 % and 14.4 %, respectively, showing a photovoltaic performance comparable to that obtained using spiro-OMeTAD. These synthetically simple and inexpensive HTMs hold promise for replacing the more expensive spiro-OMeTAD in high-efficiency perovskite solar cells.

Efficient, symmetric oligomer hole transporting materials with different cores for high performance perovskite solar cells.

Novel symmetric oligomer hole transporting materials (HTMs) incorporating 3,4-ethylenedioxythiophene (EDOT) and 2,1,3-benzothiadiazole (BTD) cores have been synthesized and tested for high performance perovskite solar cells. A maximum energy conversion efficiency of 14.23% has been achieved by employing with the electron donating EDOT unit as the core, which is comparable to that of the traditional (14.55%).

Efficient Hole Transporting Materials with Two or Four N,N-Di(4-methoxyphenyl)aminophenyl Arms on an Ethene Unit for Perovskite Solar Cells.

Novel steric bulky hole transporting materials (HTMs) with two or four N,N-di(4-methoxyphenyl)aminophenyl units have been synthesized. When the EtheneTTPA was used as a hole transporting material in perovskite solar cell, the power conversion efficiency afforded 12.77 % under AM 1.5 G illumination, which is comparable to the widely used spiro-OMeTAD based solar cell (13.28 %).

High capacity and exceptional cycling stability of ternary metal sulfide nanorods as Li ion battery anodes.

Ternary spinel NiCo2S4 nanorods are tested for the first time as anode electrodes for Li ion batteries. When the electrode is fabricated using the carboxymethyl cellulose-polyacryl amide composite binder, it is found to restrict or suppress the formation of a polymeric gel passivation layer. As a result, the electrode not only delivers excellent specific capacity, but also an outstanding rate and cyclic stability with almost no decay up to 100 charge-discharge cycles.

Stable and efficient hole transporting materials with a dimethylfluorenylamino moiety for perovskite solar cells.

Novel star-shaped hole transporting materials (HTMs) with a bis-dimethylfluorenylamino moiety have been synthesized and evaluated for high performance perovskite solar cell applications. Maximum power conversion efficiency of 14.21% has been achieved by using the HTM with a fused TPA core and the long-term stability was also shown to be comparable with that of .

Efficient perovskite solar cells with 13.63 % efficiency based on planar triphenylamine hole conductors.

A new type of hole transporting material (HTMs) with an incorporated planar amine or triphenylamine as a core unit have been prepared. The two amine derivatives were demonstrated to be efficient hole transporting materials in fabricating solid-state organic-inorganic hybrid solar cells. Perovskite-based solar cells with a planar amine derivative gave a short circuit photocurrent density (Jsc) of 20.98 m Acm(-2), an open circuit voltage (Voc) of 0.972 V, and a fill factor of 0.67, corresponding to an overall conversion efficiency of 13.63 %. The photovoltaic performance is comparable to that of the standard spiro-OMeTAD. Moreover, the device showed good stability under light soaking for 500 h. These HTMs hold promise to replace the expensive spiro-OMeTAD because of their high efficiency, excellent stability, synthesis from simple and inexpensive materials.

Star-shaped hole transporting materials with a triazine unit for efficient perovskite solar cells.

Novel star-shaped hole transporting materials with a triazine unit have been synthesized. When the new Triazine-Th-OMeTPA was used as a hole transporting material in perovskite solar cells, the power conversion efficiency reached 12.51% under AM 1.5 G (100 mW cm(-2)) illumination, showing competitive photovoltaic performance with the widely used spiro-OMeTAD based solar cell (13.45%).

Perovskite solar cells with 12.8% efficiency by using conjugated quinolizino acridine based hole transporting material.

A low band gap quinolizino acridine based molecule was designed and synthesized as new hole transporting material for organic-inorganic hybrid lead halide perovskite solar cells. The functionalized quinolizino acridine compound showed an effective hole mobility in the same range of the state-of-the-art spiro-MeOTAD and an appropriate oxidation potential of 5.23 eV vs the vacuum level. The device based on this new hole transporting material achieved high power conversion efficiency of 12.8% under the illumination of 98.8 mW cm(-2), which was better than the well-known spiro-MeOTAD under the same conditions. Moreover, this molecule could work alone without any additives, thus making it to be a promising candidate for solid-state photovoltaic application.

Graphene nanoplatelets doped with N at its edges as metal-free cathodes for organic dye-sensitized solar cells.

Challenging precious Pt-based electrocatalysts for dye-sensitized solar cells (DSSCs), graphene nanoplatelets that are N-doped at the edges (NGnPs) are prepared via simply ball-milling graphite in the presence of nitrogen gas. DSSCs based on specific nanoplatelets designated "NGnP5" display superior photovoltaic performance (power conversion efficiency, 10.27%) compared to that of conventional Pt-based devices (9.96%). More importantly, the NGnP counter electrode exhibits outstanding electrochemical stability and electrocatalytic activity with a cobalt-complex redox couple.

A simple template-free 'sputtering deposition and selective etching' process for nanoporous thin films and its application to dye-sensitized solar cells.

A facile and straightforward method is suggested to synthesize nanoporous-TiO2 thin films for dye-sensitized solar cells (DSSCs). Silver/TiO2 co-sputtering led to the formation of nanocomposite films which consisted of silver nanoclusters with surrounding TiO2 matrices, and metal particles were subsequently etched by just immersing in nitric acid. Nanoporous-TiO2 DSSCs fabricated by this simple and effective process showed power-conversion efficiencies of up to 3.4% at a thickness of only 1.8 µm, which is much superior to that of conventional nanoparticulate-TiO2 DSSCs with similar thickness.

Direct nitrogen fixation at the edges of graphene nanoplatelets as efficient electrocatalysts for energy conversion.

Nitrogen fixation is essential for the synthesis of many important chemicals (e.g., fertilizers, explosives) and basic building blocks for all forms of life (e.g., nucleotides for DNA and RNA, amino acids for proteins). However, direct nitrogen fixation is challenging as nitrogen (N2) does not easily react with other chemicals. By dry ball-milling graphite with N2, we have discovered a simple, but versatile, scalable and eco-friendly, approach to direct fixation of N2 at the edges of graphene nanoplatelets (GnPs). The mechanochemical cracking of graphitic C--C bonds generated active carbon species that react directly with N2 to form five- and six-membered aromatic rings at the broken edges, leading to solution-processable edge-nitrogenated graphene nanoplatelets (NGnPs) with superb catalytic performance in both dye-sensitized solar cells and fuel cells to replace conventional Pt-based catalysts for energy conversion.

Organic sensitizers featuring a planar indeno[1,2-b]-thiophene for efficient dye-sensitized solar cells.

An efficient organic sensitizer (JK-306) featuring a planar indeno[1,2-b]thiophene as the π-linker of a bridging unit for dye-sensitized solar cells (DSSCs) was synthesized. The sensitizer had a strong molar absorption coefficient and a red-shifted absorption band compared with JK-305, which resulted in a significant increase in the short-circuit photocurrent density. We incorporated a highly congested bulky amino group into the 2',4'-dihexyloxybiphenyl-4-yl moiety, an electron donor, to diminish the charge recombination and to prevent aggregation of the sensitizer. Under standard AM 1.5G solar conditions, JK-306-sensitized cells in the presence of co-adsorbents chenodeoxycholic acid (CDCA) and 4-[bis(9,9-dimethyl-9H-fluoren-2-yl)amino]benzoic acid (HC-A), which afforded an overall conversion efficiency of 8.37% and 8.52%, respectively. Upon changing the I(-) /I3 (-) electrolyte to the Co(II) /Co(III) redox couple, the cell gave rise to a significantly improved conversion efficiency of 10.02% with the multifunctional HC-A, which is one of the highest values reported for DSSCs with a cobalt-based electrolyte. Furthermore, the JK-306-based solar cell with a polymer gel electrolyte revealed a high conversion efficiency of 7.61%, which is one of the highest values for cells based on organic sensitizers.

N-Doped graphene nanoplatelets as superior metal-free counter electrodes for organic dye-sensitized solar cells.

Highly efficient counter electrodes (CEs) for dye-sensitized solar cells (DSSCs) were developed using thin films of scalable and high-quality, nitrogen-doped graphene nanoplatelets (NGnP), which was synthesized by a simple two-step reaction sequence. The resultant NGnP was deposited on fluorine-doped SnO2 (FTO)/glass substrates by using electrospray (e-spray) coating, and their electrocatalytic activities were systematically evaluated for Co(bpy)3(3+/2+) redox couple in DSSCs with an organic sensitizer. The e-sprayed NGnP thin films exhibited outstanding performances as CEs for DSSCs. The optimized NGnP electrode showed better electrochemical stability under prolonged cycling potential, and its Rct at the interface of the CE/electrolyte decreased down to 1.73 Ω cm(2), a value much lower than that of the Pt electrode (3.15 Ω cm(2)). The DSSC with the optimized NGnP-CE had a higher fill factor (FF, 74.2%) and a cell efficiency (9.05%), whereas those of the DSSC using Pt-CE were only 70.6% and 8.43%, respectively. To the best of our knowledge, the extraordinarily better current-voltage characteristics of the DSSC-NGnP outperforming the DSSC-Pt for the Co(bpy)3(3+/2+) redox couple (in paticular, FF and short circuit current, Jsc) is highlighted for the first time.

Planar star-shaped organic semiconductor with fused triphenylamine core for solution-processed small-molecule organic solar cells and field-effect transistors.

The symmetrical planar star-shaped organic semiconductor DMM-TPA-[DTS(BTTh(3))](3) with fused TPA core donor and three branch motifs, DTS(BTTh(3)), exhibited efficient p-type semiconducting performance in solution-processed SMOSCs and OFETs compared to the tilted star-shaped TPA-[DTS(BTTh(3))](3); a noteworthy PCE value of 4.16% was observed, with a hole mobility and on/off ratio of 7.6 × 10(-3) cm(2) V(-1) s(-1) and 5 × 10(6), respectively.

Electron-rich anthracene semiconductors containing triarylamine for solution-processed small-molecule organic solar cells.

New electron-rich anthracene derivatives containing triarylamine hole stabilizers, 2,6-bis[5,5'-bis(N,N'-diphenylaniline)-2,2'-bithiophen-5-yl]-9,10-bis-[(triisopropylsilyl)ethynyl]anthracene (TIPSAntBT-TPA) and 2,6-bis(5,5'-bis{4-[bis(9,9-dimethyl-9H-fluoren-2-yl)amino]phenyl}-2,2'-bithiophen-5-yl)-9,10-bis-[(triisopropylsilyl)ethynyl]anthracene (TIPSAntBT-bisDMFA), linked with π-conjugated bithiophene bridges, were synthesized and their photovoltaic characteristics were investigated in solution-processed small-molecule organic solar cells (SMOSCs). These new materials exhibited superior intramolecular charge transfer from triarylamine to anthracene, leading to a more electron-rich anthracene core that facilitated electron transfer into phenyl-C(61)-butyric acid methyl ester. Compared with TIPSAntBT and triarylamine, these materials show a threefold improvement in hole-transporting properties and better photovoltaic performance in solution-processed SMOSCs, with the best power conversion efficiency being 2.96 % at a high open-circuit voltage of 0.85 V.

Facile synthesis of fluorine-substituted benzothiadiazole-based organic semiconductors and their use in solution-processed small-molecule organic solar cells.

A facile new protocol for the synthesis of iodinated derivatives of fluorinated benzothiadiazoles is demonstrated for the production of p-type semiconducting materials. The newly synthesized small-molecule compounds bis[TPA-diTh]-MonoF-BT and bis[TPA-diTh]-DiF-BT exhibited a power conversion efficiency of 2.95% and a high open-circuit voltage of 0.85 V in solution-processed small-molecule organic solar cells.

New type of organic sensitizers with a planar amine unit for efficient dye-sensitized solar cells.

A new type of organic sensitizers incorporating a planar amine unit have been synthesized and demonstrated to be a highly efficient sensitizers, showing evidence of lateral interactions on the TiO(2) surface. Under standard global air mass 1.5 solar conditions, the JK-98 sensitized cell gave a short circuit photocurrent density (J(sc)) of 16.78 mA cm(-2), an open-circuit voltage (V(oc)) of 0.745 V, and a fill factor (ff) of 0.70, corresponding to an overall conversion efficiency (η) of 8.71%.