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Poly(3,4-ethylenedioxythiophene) (PEDOT) aggregate-deposited counter electrodes (CEs) were applied to bifacial dye-sensitized solar cells with a cobalt complex electrolyte. The high transparency and excellent electrochemical activity of PEDOT CEs result in an impressive cell bifaciality of 0.92 under standard test conditions (AM 1.5G, 100 mW cm−2), and maximum power production of 11.3% under realistic conditions with an effective albedo of 50%. [ABSTRACT FROM AUTHOR]

Defect passivation with organic molecules is a significant strategy to improve perovskite solar cells (PSCs). However, because of carrier extraction and recombination in the bottom of the perovskite film, solar cell improvement is hindered. In this work, molecules of sodium 3-oxo-3H-spiro [isobenzofuran-1,9′-xanthene]-3′,6′-bis(olate) (SSB) were pre-buried into the SnO2 electron transport layer (ETL), which resulted in modification of the SnO2 and perovskite interface. This SSB molecular treatment improved the quality of the SnO2 film. Moreover, the SSB molecule realized interfacial interaction with SnO2 and perovskite, and substantially reduced the trap state density and enhanced charge extraction. As a result, the photovoltaic performances of the PSCs with the SSB devices improved, achieving an impressive efficiency of up to 22.64%. Additionally, the SSB devices without encapsulation demonstrated enhanced stability in air (at approximately 25 °C at approximately 30% humidity) and in an N2 environment under continuous illumination. [ABSTRACT FROM AUTHOR]

Methoxy-free donors are an emerging class of alternative methoxy triphenylamine materials toward stable organic hole-transporting materials (HTMs). However, low cost, stable and efficient methoxy-free donors are scarce. Moreover, the lack of a molecular design strategy limits the further development of methoxy-free donor-based HTMs. This study reports a newly developed low cost hybrid methoxy-free donor (viz., indeno[2,1-b]carbazole) as well as a triple π-bridge strategy to enhance the performance of methoxy-free donor-based HTMs. Based on this strategy, two new indeno[2,1-b]carbazole HTMs, termed M136 and M138, were tailor-made and tested in perovskite solar cells (PSCs). Upon incorporating the triple π-bridges (i.e. thiophene-dithieno[3,2-b:2′,3′-d]pyrrole-thiophene and thiophene-3,4-ethylenedioxythiophene-thiophene), the resulting indeno[2,1-b]carbazole HTMs (M136 and M138) exhibit a significantly increased hole mobility, improved charge extraction and minimized trap-assisted recombination as compared to M135 and M137 with unitary and binary bridges, respectively. Consequently, the optimized devices based on M138 achieved an efficiency of 21.37%, which is among the top efficiencies for PSCs based on methoxy-free donor HTMs. The findings demonstrate that indeno[2,1-b]carbazole is an excellent methoxy-free donor. In addition, this work underscores the effectiveness of π-bridge engineering to improve the performance of methoxy-free donor-based HTMs. [ABSTRACT FROM AUTHOR]

A photoanode fabricated with agglomerated zinc stannate nanoparticles was applied to dye sensitized solar cells (DSCs) based on cobalt complex mediators. The resultant devices yield an impressive power conversion efficiency of 8.1% under 100 mW cm−2 (AM1.5) light irradiation, which demonstrates the feasibility of use of zinc stannate photoanodes in iodine-free DSCs. [ABSTRACT FROM AUTHOR]

The property of charge extraction at the contact between the perovskite and electron selective layer (ESL) is vital to the photovoltaic performance of perovskite solar cells (PSCs). The J–V hysteresis phenomenon is frequently observed when the PSC is limited by inefficient charge transfer across the perovskite/ESL interface. Drift–diffusion simulations are performed so as to correlate the hysteresis with the quality of the perovskite/ESL junction. A generalized charge exchange model is introduced into drift–diffusion equations for describing the dynamics of charge extraction at the perovskite/ESL contact. Our simulations demonstrate that inefficient charge extraction is one of the causes of j–V hysteresis. This is because limited charge transfer gives rise to a depletion domain in the ESL, and hence promotes the interfacial accumulation of charge carriers as well as movable ions. Furthermore, it is found that the incorporation of surface recombination into drift–diffusion simulations enables the loss in open circuit voltage to be simulated in PSCs with different charge transfer properties. The simulation results indicate that j–V hysteresis can be suppressed by improving the charge extraction property and suppressing surface recombination. [ABSTRACT FROM AUTHOR]

Novel binaphthylamine-based hole-transport molecules with different side-chains were designed and synthesized. The obtained materials exhibit comparable optoelectronic properties and molecular configuration, but distinct film properties. In this work, which was inspired by the structural feature of polymer and π–π stacking strategy of carbon nanotubes with large π-spacers, two kinds of optimized hole-transport molecules with amine and methyl units were attached to multi-walled carbon nanotubes by physisorption, and were further used to fabricate inverted perovskite solar cells. A non-encapsulated device based on a hole-transporting material with multi-walled carbon nanotubes gives a power conversion efficiency of 17.17%, comparable to that of the pristine hole-transport material (17.32%). More importantly, the former exhibits a higher device stability than the later. Introduction of carbon nanotubes to hole-transport materials provides a new method for improving the device stability of inverted perovskite solar cells. [ABSTRACT FROM AUTHOR]

Four new hole transporting materials (HTMs), M107–M110, based on thieno[3,2-b]indole cores have been designed and employed in perovskite solar cells. The perovskite solar cells based on M109 exhibit a leading efficiency of 18.14% with a photovoltage over 1.11 V. [ABSTRACT FROM AUTHOR]

Dithieno[3,2-b:2′,3′-d]pyrrole (DTP) derivatives are one of the most important organic photovoltaic materials due to better π-conjugation across fused thiophene rings. In this work, two new hole transport materials (HTMs), H16 and H18, have been obtained through a facile synthetic route by cross linking triarylamine-based donor groups with a 4-(4-methoxyphenyl)-4H-dithieno[3,2-b:2′,3′-d]pyrrole (MPDTP) and N-(4-(4H-dithieno[3,2 b:2′,3′-d]pyrrol-4-yl)phenyl)-4-methoxy-N-(4-methoxyphenyl)aniline (TPDTP) unit, respectively. The H16 HTM outperforms the H18 in terms of conductivity, hole mobility, and hole transport at the interface. This result could be attributed to the enhancement of the conductivity, hole mobility and high quality of the film exerted by the MPDTP core. The optimized device based on H16 exhibits a high power conversion efficiency (PCE) of 18.16%, which is comparable to that obtained with the state-of-the-art-HTM spiro-OMeTAD (18.27%). Furthermore, the long-term aging test shows that the H16 based device has good stability after two months of aging under controlled (20%) humidity in the dark. Importantly, the synthesis cost of H16 is roughly 1/5 of that of spiro-OMeTAD. The present finding highlights the potential of DTP based HTMs for efficient PSCs. [ABSTRACT FROM AUTHOR]

Self-assembly of organic sensitizer layers in cobalt complex-based DSCs was studied to elucidate its role in reducing the loss of charge recombination. DSCs with various dye loadings were fabricated by dye desorption without the aid of basic solvent. The FT-IR and UV results indicate the deprotonation of the anchoring organic sensitizers, which influences the conduction band of TiO2 remarkably by changing the surface potential. Positive band edge shifts and a decrease of the recombination rate constant are demonstrated to be the main factors affecting energy loss at open circuit. In contrast, absorbed photon conversion efficiency (APCE) analyses illuminate the crucial role of the packing of the anchoring sensitizer in reducing recombination loss at short circuit. This is further supported by numerical simulations, which show that APCE is primarily dependent on the recombination rate constant rather than the band edge shift at short circuit. These results highlight the importance of self-assembly of sensitizers with insulating groups in retarding charge recombination by forming overlapping molecular layers. [ABSTRACT FROM AUTHOR]

Thiophene derivatives, including thieno[3,2-b][1]benzothiophene (TBT), benzo[b]thiophene (BT), 2-phenylthieno[3,2-b]thiophene (PTT) and 2-phenylthiophene (PT), have been introduced as donors for the construction of triarylamine organic dyes (M52, M53, M56, M57 and M52A). The absorption, electrochemical and photovoltaic properties as well as the stabilities of these dyes are systematically investigated and compared with the reference dye (M55), whose donor is composed of the hexyloxybenzene (HOB) unit. It is found that introducing the TBT, BT, PTT or PT donors positively shifted the HOMO and LUMO levels of the organic dyes, providing a larger driving force for regeneration and reducing the energy loss for electron injection. In addition, we found that M52, which contains the TBT unit, exhibited better photovoltaic performance and photostability as compared to the reference dye. In contrast, M53 displayed the lowest efficiency and stability of these dyes, indicating that the BT unit is not a good building block for donors. Interestingly, upon the incorporation of the mixed donor (TBT–HOB), M52A achieved a desirable driving force for regeneration without a loss in light absorption, thus resulting in a further improved photovoltaic performance with respect to that of M52. This work demonstrates that introducing donors based on thiophene derivatives is a good strategy for tuning the energy levels and thereby enhancing the efficiency of the resulting devices. [ABSTRACT FROM AUTHOR]

Organolead iodide perovskite showing tubular morphology was fabricated on mesoporous TiO2 film via a one-step spin-coating procedure. These perovskite tubes with the external diameter of 1 μm were found to facilitate the charge separation at perovskite/hole-transport material (HTM) interfaces. This engenders a tubular perovskite device showing a higher fill factor over the device with planar perovskite, and improves power conversion efficiency accordingly. [ABSTRACT FROM AUTHOR]

We report two new triarylamine-cyanoacrylic acid based push–pull dyes, X76 and X77, featuring the π-conjugated linkers of dihexyl- and dihexyloxybenzene-substituted dithieno[2,3-d:2′,3′-d′]thieno[3,2-b:3′,2′-b′]dipyrrole (DTDP), respectively. The absorption, electrochemical, and photovoltaic properties for all sensitizers have been systematically investigated. Both dyes containing a DTDP moiety showed good light harvesting ability as compared to that of the reference dye incorporating the hexyl-substituted dithieno[3,2-b:2′,3′-d]pyrrole (DTP) linker. Moreover, the substituents of DTDP moiety significantly influenced the electrochemical and photovoltaic properties of the dyes. The incident photon-to-current efficiency (IPCE) of the X77-based device is higher at longer wavelengths, and extends to nearly 800 nm. A dye-sensitized solar cell employing the X77 photosensitizer and the Co-bpy electrolyte exhibits a power conversion efficiency of 6.6% measured under the 100 mW cm−2 simulated AM1.5 sunlight. [ABSTRACT FROM AUTHOR]

An efficient method for the synthesis of phosphoric fluoride via oxidative coupling between hydrophosphine oxide and NaF is reported. DDQ serves as the oxidizing reagent as well as the hydrogen acceptor. The process involves a Cu(II) catalysis and exhibits great functional group tolerance under mild reaction conditions. [ABSTRACT FROM AUTHOR]

The first Cu(I)-catalyzed cross-coupling reaction by hydrogen (H2) removal for the stereoselective synthesis of 3-phosphoindoles is reported. Going beyond the oxidative dehydrogenative coupling reactions reported recently, this reaction completely omits the oxidant and base, producing hydrogen (H2) as the only byproduct. [ABSTRACT FROM AUTHOR]

Dithieno[3,2-b:2′,3′-d]pyrrole (DTP) compounds with strong electron-donating ability are promising spacers for photosensitizers. A series of new arylamine organic dyes bearing N-heterocycle-substituted DTP spacers has been designed and synthesized for iodine-free dye-sensitized solar cells (DSCs). The absorption, electrochemical, and photovoltaic properties for all the sensitizers have been systematically investigated. It was found that the incorporation of a dihexylaniline or hexylcarbazole unit, instead of a benzene unit, can notably retard the charge recombination at the titania–electrolyte interface, thus improving the cell photocurrent and photovoltage. Furthermore, we found a significant efficiency enhancement upon prolonging the adsorption time during the dye uptake from solution. When the dye adsorption was performed for 36 hours, the photovoltaic performance parameters measured under standard reporting conditions improved, in comparison to cells stained for 12 hours. The effects of adsorption time, correlated dye load amounts and electron lifetime were also scrutinized in terms of light-harvesting, interfacial kinetic parameters, as well as their joint contribution to the photovoltaic performance. Profiting from the favorable influence that the 36 hours dye uptake exerts on photovoltaic performance, we have realized a highly efficient iodine-free DSC displaying a power conversion efficiency of 8.20% measured at 100 mW cm−2 simulated AM1.5 conditions. [ABSTRACT FROM AUTHOR]

The development of arylamine photosensitizers with high extinction coefficients, and suitable electronic structures and steric properties is necessary for improving the efficiency of dye-sensitized solar cells (DSCs) employing iodine-free redox shuttles. A new truxene-based organic sensitizer, M20, incorporating a 3,4-ethylenedioxythiophene (EDOT) moiety as an electron donor was synthesized and compared to its reference sensitizer, M4. M20 sensitized DSCs employing the Co(ii/iii) tris(1,10-phenanthroline)-based redox electrolyte exhibit a short circuit photocurrent of 11.8 mA cm−2, an open circuit voltage of 903 mV, and a fill factor of 0.69, corresponding to an overall conversion efficiency of 7.35% under standard AM 1.5 sunlight, which is higher than that of 6.86% for equivalent M4 sensitized DSCs. The effects of 4-tert-butylpyridine (TBP) as an additive on the photovoltaic performance of truxene-dye-sensitized nanocrystallineTiO2 solar cells were also investigated. [ABSTRACT FROM AUTHOR]

Three dithieno[3,2-b:2′,3′-d]pyrrole (DTP) units with different hexyloxyphenyl (HOP) substituents have been developed for triphenylamine organic dyes (XS54–XS56). The introduction of the 4-HOP-DTP unit has resulted in a stronger light harvesting capacity, accounting for the observed photocurrent enhancement in the case of XS54, while the 2-HOP-DTP/2,4-HOP-DTP units induce a strikingly large photovoltage improvement in the cases of XS55 and XS56 due to their higher steric hindrance. [ABSTRACT FROM AUTHOR]

The property of charge extraction at the contact between the perovskite and electron selective layer (ESL) is vital to the photovoltaic performance of perovskite solar cells (PSCs). The J-V hysteresis phenomenon is frequently observed when the PSC is limited by inefficient charge transfer across the perovskite/ESL interface. Drift-diffusion simulations are performed so as to correlate the hysteresis with the quality of the perovskite/ESL junction. A generalized charge exchange model is introduced into drift-diffusion equations for describing the dynamics of charge extraction at the perovskite/ESL contact. Our simulations demonstrate that inefficient charge extraction is one of the causes of j-V hysteresis. This is because limited charge transfer gives rise to a depletion domain in the ESL, and hence promotes the interfacial accumulation of charge carriers as well as movable ions. Furthermore, it is found that the incorporation of surface recombination into drift-diffusion simulations enables the loss in open circuit voltage to be simulated in PSCs with different charge transfer properties. The simulation results indicate that j-V hysteresis can be suppressed by improving the charge extraction property and suppressing surface recombination.

Two new truxene-based organic sensitizers (M15 and M16) featuring high extinction coefficients were synthesized for dye-sensitized solar cells employing cobalt electrolyte. The M16-sensitized device displays a 7.6% efficiency at an irradiation of AM1.5 full sunlight.

PPh3-catalyzed alpha-addition reactions of 1-(o-hydroxyaryl)-1,3-diketones to terminal alkynoates involving carbon-carbon bond cleavage to give multifunctional vinylesters are described.

Two cyano-bridged heterobimetallic coordination polymers [Mn[Au(CN)2]2(H2O)2]n (1) and [KFe[Au(CN)2]3]n (2), have been synthesized from [Au(CN)2]- building blocks and structurally characterized. In both complexes aurophilicity play an important role in determining the 3D open microporous framework and the interpenetrating triple framework for 1 and 2, respectively. Both aqueous solutions of 1 and 2 display interesting luminescent properties.