Presynthesized high-quality CdS/CdSe inverted type-I core/shell structure QDs have been deposited onto TiO(2) electrodes after first coating with bifunctional linker molecules, mercaptopropionic acid (MPA), and the resulting quantum dot sensitized solar cells (QDSCs) exhibited record conversion efficiency of 5.32% (V(oc) = 0.527 V, J(sc) = 18.02 mA/cm(2), FF = 0.56) under simulated AM 1.5, 100 mW cm(-2) illumination. CdS/CdSe QDs with different CdSe shell thicknesses and different corresponding absorption onsets were prepared via the well-developed organometallic high-temperature injection method. MPA-capped water-dispersible QDs were then obtained via ligand exchange from the initial organic ligand capped oil-dispersible QDs. The QD-sensitized TiO(2) electrodes were facilely prepared by pipetting the MPA-capped CdS/CdSe QD aqueous solution onto the TiO(2) film, followed by a covering process with a ZnS layer and a postsintering process at 300 °C. Polysulfide electrolyte and Cu(2)S counterelectrode were used to provide higher photocurrents and fill factors of the constructed cell devices. The characteristics of these QDSCs were studied in more detail by optical measurements, incidental photo-to-current efficiency measurements, and impedance spectroscopy. With the combination of the modified deposition technique with use of linker molecule MPA-capped water-soluble QDs and well-developed inverted type-I core/shell structure of the sensitizer together with the sintering treatment of QD-bound TiO(2) electrodes, the resulting CdS/CdSe-sensitized solar cells show a record photovoltaic performance with a conversion efficiency of 5.32%.

We report two new molecularly engineered push-pull dyes, i.e., YA421 and YA422, based on substituted quinoxaline as a π-conjugating linker and bulky-indoline moiety as donor and compared with reported IQ4 dye. Benefitting from increased steric hindrance with the introduction of bis(2,4-dihexyloxy)benzene substitution on the quinoxaline, the electron recombination between redox electrolyte and the TiO2 surface is reduced, especially in redox electrolyte employing Co(II/III) complexes as redox shuttles. It was found that the open circuit photovoltages of IQ4, YA421, and YA422 devices with cobalt-based electrolyte are higher than those with iodide/triiodide electrolyte by 34, 62, and 135 mV, respectively. Moreover, the cells employing graphene nanoplatelets on top of gold spattered film as a counter electrode (CE) show lower charge-transfer resistance compared to platinum as a CE. Consequently, YA422 devices deliver the best power conversion efficiency due to higher fill factor, reaching 10.65% at AM 1.5 simulated sunlight. Electrochemical impedance spectroscopy and transient absorption spectroscopy analysis were performed to understand the electrolyte influence on the device performances with different counter electrode materials and donor structures of donor-π-acceptor dyes. Laser flash photolysis experiments indicate that even though the dye regeneration of YA422 is slower than that of the other two dyes, the slower back electron transfer of YA422 contributes to the higher device performance.

A postsynthesis assembly approach, an ex situ ligand exchange route, was developed for fast (within 2 h) and high loading (34% coverage) deposition of CdSe QDs on TiO(2) films. With the combination of high-quality QD sensitizers and the effective deposition technique, a record photovoltaic performance with an efficiency of 5.4% was observed for the resulting cell device.

at the surface and grain boundaries, acting as carrier recombination centers and greatly limiting the open-circuit voltage (V oc ) of PSCs. Meanwhile, these trap states can lead to the infiltration of moisture and oxygen into perovskite, and subsequently harm the device stability in ambient environment. [23][24][25][26] These trap states at the surface and grain boundaries are most likely induced by ions migration, oxidization of I − or evaporation of methylammonium iodide (MAI), which are mainly manifested as under-coordinated metal cations or halide anions. [27][28][29] So far, a variety of passivation materials (also known as passivator) have been added into perovskite films to induce defect passivation through forming coordination with under-coordinated metal cations or halide anions. For instance, phenyl-C61-butyric acid methyl ester (PCBM), as a Lewis acid could passivate the trap states by forming coordination with halide ions and thus eliminate the notorious photocurrent hysteresis. [28,30] On the contrary, Snaith and co-workers demonstrated that Lewis base molecules, such as thiophene or pyridine, could heal the trap states by forming coordination with under-coordinated Pb 2+ ions in perovskite films. [31] Since these initial results of defect passivation by reducing the uncoordinated ions in perovskite layer is proven to be effective, a defect passivator in perovskite layer should have more room for improvement. For example, a well-designed passivator in the perovskite layer should take the defect coordination and device air stability into consideration simultaneously. Thus, more effort is required to understand how to choose a suitable passivator in the perovskite layer.Among the large selection of functional groups, carboxyl (COOH) has been effectively used in other photovoltaic device as an indispensable anchoring group due to the strong coordination with metal oxide. [32] In the case of perovskite films, COOH is also found to have the interaction with perovskite films. [33,34] Small molecules such as amino acids, [35] acetate acids [8] were used to crosslink the perovskite boundaries or assist the crystallization process. However, the effect of charge recombination which is critical for the device performance is rarely mentioned in the previous work. It may because of small molecules were used as small amount of additives in the perovskite film which randomly distributed among the crystal boundaries. As the defects of perovskite film mainly locate at the top surface, [28] the controlling of stereochemical configuration is required for the film surface passivation.Organic-inorganic halide perovskites are efficient absorbers for solar cells. Nevertheless, the trap states at the surfaces and grain boundaries are a detri mental factor compromising the device performance. Here, an organic dye (AQ310) is employed as passivator to reduce the trap states of the perovs kites and promote better stability. The results demonstrate that the trap states of perovskite are minimized by the presence of AQ310's CO...

Two novel metal-free dyes (DPP-I and DPP-II) with a diketopyrrolopyrrole (DPP) core were synthesized for dye-sensitized solar cells (DSSCs). The absorption spectra and electrochemical and photovoltaic properties of DPP-I and DPP-II were extensively investigated. Electrochemical measurement data indicate that the tuning of the HOMO and LUMO energy levels can be conveniently accomplished by alternating the π-conjugated systems. Besides, coadsorption of chenodeoxycholic acid (CDCA) can hinder the formation of dye aggregates and might improve electron injection yield and, thus, J sc. This has also led to a rise in the photovoltage, which is attributed to the decrease of charge recombination. The DSSC based on dye DPP-I showed better photovoltaic performance: a maximum monochromatic incident photon-to-current conversion efficiency (IPCE) of 80%, a short-circuit photocurrent density (J sc) of 9.78 mA cm−2, an open-circuit photovoltage (V oc) of 605 mV, and a fill factor (FF) of 0.69, corresponding to an overall conversion efficiency of 4.14% under standard global AM 1.5 solar light condition. This work suggests that the metal-free dyes based on a DPP core are promising candidates for improvement of the performance of DSSCs.

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Polymer heterojunctions (PHJs) have emerged as promising photocatalysts for the photocatalytic hydrogen evolution (PHE). Nevertheless, most PHJs exhibit unsatisfactory hydrogen evolution rate (HER), primarily attributing to their own high-energy Frenkel excitons and poor light capturing ability. In this paper, a molecular engineering strategy is developed to further broaden spectral response range and simultaneously accelerate Frenkel excitons dissociation within PHJs. For this purpose, three donor-acceptor (D-A) conjugated polymers/g-C 3 N 4 heterojunctions with alternative donor units (fluorene, carbazole, N-annulated perylene for P1, P2, and P3, respectively) and the invariant acceptor unit (benzothiadiazole) have been designed and fabricated for efficient PHE. Experimental results show that copolymerizing different donor units into the polymer skeleton not only extends the visiblelight response range but also promotes photoexciton separation within polymer/g-C 3 N 4 PHJs. Notably, copolymerizing the strongest electron donor unit (N-annulated perylene) achieves the best light capture ability and the most effective photoexcitation separation of the P3/g-C 3 N 4 , leading to significantly increase HRE of 13.0 mmol h −1 g −1 with a recorded apparent quantum yield of 27.32% at 520 nm. Importantly, the Type II heterojunction mechanism within P3/CN was first proved by theoretical calculation. This work provides a promising strategy for reasonably developing efficient PHJs for solar fuel production.

Compared with traditional one‐photon fluorescence imaging, two‐photon fluorescence imaging techniques have shown advantages such as increased penetration depth, lower tissue autofluorescence, and reduced photo­damage, and therefore are particularly useful for imaging tissues and animals. In this work, the design and synthesis of two novel DPP‐based compounds with large two‐photon absorption (2PA) cross‐sections (σ ≥ 8100 GM) and aggregation‐induced emission (AIE) properties are reported. The new compounds are red/NIR emissive and show large Stokes shifts (Δλ ≥ 3571 cm−1). 1,2‐Distearoyl‐sn‐glycero‐3‐phosphoethanol amine‐N‐[maleimide(polyethylene glycol)‐2000 (DSPE‐PEG‐Mal) is used as the encapsulation matrix to encapsulate DPP‐2, followed by surface functionalization with cell penetrating peptide (CPP) to yield DPP‐2‐CPP nanoparticles with high brightness, good water dispersibility, and excellent biocompatibility. DPP‐2 nanoparticles have been used for cell imaging and two‐photon imaging with clear visualization of blood vasculature inside mouse ear skin with a depth up to 80 μm.