•Three synthesized chlorophylls were employed for cell imaging for the first time.•Chlorophylls with different substituent groups show varying changes after loaded.•Such low-costed nanoparticles show bright fluorescence signals and low toxicity.Herein three synthesized chlorophyll derivatives (ZnChl-1, H2Chl-2, ZnChl-2) featuring hydrophilic hydroxy/carboxy groups were employed as precursors for fluorescent organic nanoparticles (NPs) with biocompatible Pluronic F127 as the encapsulation matrix for the first time. Such red NPs exhibited broad absorption bands and high hydrophilicity. Three chlorophyll derivatives with different substituent groups show varying degrees of changes after loaded with F127. As a result, ZnChl-2 exhibited the best retainable photoluminescence yield after encapsulation among these chlorophyll derivatives. It reveals that ZnChl-2@F127 is the most suitable NPs for cell imaging by comparing not only different three chlorophyll derivatives, but also free ZnChl-2 and ZnChl-2@F127. Application of ZnChl-2@F127 NPs for cancer cell imaging was successfully demonstrated and such chlorophyll-based NPs showed bright fluorescence signals and low toxicity. These studies indicate that the F127 encapsulated low-costed chlorophyll derivatives NPs are efficient fluorescent dyes for biological imaging. It is further directed towards photodynamic therapy based on chlorophyll derivatives.

Although ZnO is a compatible electron transport layer (ETL) for perovskite solar cells (PSCs), the fact that MAPbI3 easily undergoes thermal decomposition on a low-temperature processed ZnO surface limits the use of one-step deposition of perovskite and hence the resulting photovoltaic performance. Herein, we demonstrate triple cation perovskite (Csx(MA0.17FA0.83)(100−x)Pb(I0.83Br0.17)3) prepared with a one-step deposition method as a stable light absorber in highly efficient PSCs with low-temperature processed ZnO as the ETL. The photovoltaic performance of the investigated PSCs was dependent on both the annealing temperature of the perovskite film and the composition of the Cs element in the perovskite structure. A remnant PbI2 passivation phase in the perovskite layer, in which the composition is Cs6(MA0.17FA0.83)94Pb(I0.83Br0.17)3 and the annealing temperature is 95 °C, leads to the highest power conversion efficiency of ∼18.9%, which is a record-high so far for low-temperature processed ZnO-based PSCs. Importantly, this PSC exhibits excellent environmental durability and photostability, which are critical characteristics for further commercialization of low-temperature processed PSCs.

•The Dye-TiO2/electrolyte/Ni/WO3 system was successfully set.•First used solution-processed WO3 mesoporous film as electron-storage electrode.•Get a discharge capacity which is seven times more than reported.In this work, we demonstrated the dye-sensitized solar rechargeable batteries devices sharing a structure of Dye-TiO2/electrolyte/Ni/WO3. The WO3 film was prepared by a simple sol-gel process exhibit high cavities and large surface area allowing efficient chemical/electrical reactions. The WO3 films with 2 ± 0.5 μm in thickness as charge collection electrodes exhibited a high energy density over other materials reported thus far. Under irradiation energy of 7.5 mWcm−2 in the photo-charging, the discharging time sustained 1758 s at the current density of 0.05 mA cm−2 in dark, the first specific discharge capacities of WO3 nano-film reach 40.6 mAh g−1 (0.0244 mAh cm−2). This work substantially pushes forward the easy processing solar rechargeable batteries for future potential applications.

•Near-infrared absorption bacteriochlorophyll-based solar cells are fabricated.•The bacteriochlorophyll can self-assemble into aggregates by π-π staking.•The absorption peak of bacteriochlorophylls-1/2 aggregates red shift to 860 nm.•The NIR absorption of aggregates can transfer into photocurrent efficiently.In this paper, we investigate two bacteriochlorophyll (BChl) derivatives, namely methyl (pyro)bacteriopheophorbide a [BChl-(2)1], with excellent absorption in near-infrared regions as donor materials for organic solar cells (OSCs). In the meantime, we prepare two methyl (pyro)pheophorbide a [Chl-(2)1] as reference to make a comparison. Compared to the small red-shifts of absorption bands of Chls-1/2 after forming the thin film through spin coating of the homogeneous solution, the absorption spectra of BChls-1/2 exhibited larger red-shifts from the absorption peak at 750 nm in the solution to the absorption peak at 860 nm after forming the solid film. This significant absorption shift is attributed to the formation of J-type aggregates by intermolecular π-π stacking among the BChl-1/2 molecules. What’s more the absorbed sunlight of the BChls-1/2 aggregates at the near-infrared (NIR) region can be transferred into photocurrent which can be proved from the EQE indicating the energy and electron transferring between BChl aggregates are efficient. The optimized power conversion efficiency (PCE) value of 1.43% under standard AM1.5 mW/cm2 sunlight was achieved with the BChl-1: C70 planar-heterojunction (PHJ) cells.Download high-res image (106KB)Download full-size image

•Carboxylated chlorophyll-a derivatives as efficient sensitizer for photocatalytic H2 evolution.•Chl-2/Pt/TiO2 photocatalyst exhibited best H2-evolution rate of 0.79 μmol h−1 g−1.•Carboxy anchoring group at different positions of the chlorin macrocycles played an important role in photocatalytic activity.Chlorophylls (Chls) are naturally occurring photosensitizers having an excellent visible and near-infrared light absorption property. Herein, we employ three Chl a derivatives as sensitizers in a TiO2-based photocatalytic system for H2 evolution with ascorbic acid as the sacrificial reagent under visible light (λ > 400 nm). The H2-evolution activity of these Chl a derivatives depends on a carboxy group in the C3- and/or C17-substituent(s). The concentration of 1 mg/ml dye/Pt/TiO2 powder suspended in an aqueous solution with ascorbic acid as the sacrificial reagent gives the highest H2-evolution rate. The fact that Chl-2 with a carboxy group on the C3 position of the chlorin macrocycle gives the highest H2-evolution rate of 0.79 μmol h−1 is ascribed to the lowest charge recombination rate between Chl-2 and TiO2 among all Chls investigated. This work provides us with important information in synthesizing more favorable molecular structure of Chl derivatives for the highly efficient photocatalytic H2 evolution from water splitting.Download high-res image (135KB)Download full-size image

Despite the potential of ZnO as the electron collection material for low-temperature processed perovskite solar cells (PSCs), previous investigations revealed that the CH3NH3PbI3-based perovskite rapidly decomposes on ZnO at elevated temperature through a deprotonation process (base-induced reaction) that reduces thermal stability. To solve this thermal instability issue and to further enhance the photovoltaic performance, we employed a (FA)-based perovskite, i.e., FAPbI3 as the light absorber in ZnO-based PSCs. The photovoltaic performance of the investigated FAPbI3 solar cells was clearly dependent on both the pre-heating of the PbI2 precursor and post-annealing of the FAPbI3 film in the solar cell fabrication procedure. The highest power conversion efficiency of up to 16.1% was achieved under AM 1.5 simulated sunlight illumination, in which the pre-heating and post-annealing temperatures were 100 °C and 145 °C, respectively. Importantly, the thermostability of the perovskite film on ZnO was substantially improved with FAPbI3 owing to basically the robust nature of FA compared with methylammonium (MA) in CH3NH3PbI3. Moreover, FAPbI3-based PSCs exhibited excellent photostability and small J–V hysteresis, which are all useful characteristics for further commercialization of low-temperature processed ZnO solar cells.

•The first report on ZnO–SnO2 as electron collection layer for perovskite solar cell.•The ZnO–SnO2 electron collection layers are low-temperature-processed.•An optimal ZnO–SnO2 (2:1 weight ratio in solution) gives the relatively high PCE.•The ZnO–SnO2 thin films exhibit better thermal stability of CH3NH3PbI3.•The PCE of the optimized device was further improved by introducing the Al2O3 layer.Electron collection layer (ECL) is one of the most important fundamentals to determine the power conversion efficiency (PCE) in organometal halide-based perovskite solar cells (PSCs). Herein, we prepared ZnO–SnO2 nanocomposites with different Zn/Sn ratios at low temperature as ECLs for CH3NH3PbI3-based planar-structured PSCs. ZnO–SnO2 nanocomposite with the optimal ~89 mol% of the ZnO content gives higher PCE than the ZnO for the best fabricated PSC. The photoluminescence spectroscopies measured in both steady and transient states and the electrochemical impedance spectroscopy were carried out to characterize the interface of CH3NH3PbI3 and different ECLs, namely ZnO, ZnO–SnO2 composite, and SnO2. The high PCE of PSCs based on the ZnO–SnO2 nanocomposite ECL was thus attributed to joint contributions of the high charge extraction efficiency and large charge recombination resistance both on the CH3NH3PbI3/ECL interface. The thermal stability of CH3NH3PbI3 absorber and the device stability of the corresponding PSC are both dependent on the ECLs in the order: SnO2>ZnO–SnO2 >ZnO, suggesting that the hydroxyl-induced degradation of CH3NH3PbI3 may be predominant in the ambient air environment in the initial ~700 h. The PCE of the optimized device was further improved to 15.2% by introducing the low-temperature processable Al2O3 as a capping layer to the ZnO–SnO2 composite.Download high-res image (239KB)Download full-size image

We demonstrated SnO2 films prepared by sinter-less spin-coating processes as an electron selective contact for CH3NH3PbI3-based planar-heterojunction perovskite solar cells (PSCs). A modified sequential deposition method, in which the grain size of PbI2 precursors was controlled by an equivalent solvent vapor annealing (SVA) process, was used to prepare the perovskite layer on SnO2. With this SVA process, the remnant PbI2 nanocrystals can stably occur at the interface of CH3NH3PbI3/SnO2 to carry out a passivation effect. The photovoltaic performance of SnO2-based PSCs is dependent on both the SVA time and the thickness of the perovskite layer. The optimized PSC device achieves the best power conversion efficiency of up to 13% under the AM 1.5 simulated sunlight illumination, which is highly durable over 30 days of storage time with exposure to the ambient air environment.

A two-step sequential deposition method has been extensively employed to prepare the CH3NH3PbI3 active layer from the PbI2 precursor in perovskite solar cells (PSCs). The variation of the photovoltaic performance of PSCs made by this method was always attributed to different dipping times that induce complete/incomplete conversion of PbI2 into CH3NH3PbI3. To solve this issue, we employed a solvent vapor annealing (SVA) method to prepare PbI2 crystallites with large grain size for preparation of high quality perovskite. With this method, the increased PbI2 dipping time in CH3NH3I solution was found to reduce the photovoltaic performance of resulting PSCs without a significant change in PbI2/CH3NH3PbI3 contents in the perovskite films. We attribute this abnormal reduction of the photovoltaic performance to intercalation/deintercalation of the PbI2 core with a CH3NH3PbI3 shell, which causes the doping effect on both the PbI2 and CH3NH3PbI3 crystal lattices and the formation of a CH3NH3PbI3 capping layer on the surface, as revealed by UV–vis absorption, X-ray diffraction, FT-IR, and scanning electron microscope measurements. Based on our findings, a multistep dipping-drying process was employed as an alternative method to improve the crystalline quality. The method achieved power conversion efficiency up to 11.4% for the compact layer free PSC sharing a simple device structure of ITO/perovskite/spiro-OMeTAD/Ag.Keywords: compact layer free; low-temperature-processed device; PbI2 intercalation; perovskite solar cells; solvent vapor annealing

•Two different chlorophyll-sensitized solar cells are fabricated and compared.•Cost-effective ZnChl-1 is used as the hole transporter.•The carrier mobility of ZnChl-1 is estimated and confirmed.•We provided a new possibility of using bio-resources for electricity production.The intriguing properties of extremely efficient delocalization and migration of excitons in chlorophyll (Chl) J-type aggregates have inspired intense research activities toward their structural understanding, functional interpretation and mimicry synthesis. Herein, we demonstrated the J-aggregates of zinc methyl 3-devinyl-3-hydroxymethyl-pyropheophorbide a (ZnChl-1) generated by spin-coating method for the application as a hole transporter in titania-based solar cells using methyl trans-32-carboxypyropheophorbide a (H2Chl-2) or its zinc complex (ZnChl-2) as the sensitizer. The effective carrier mobility of the J-aggregates films was determined by the organic field-effect transistor to be 6.2 × 10−4 cm2 V−1 s−1. Solar cells sharing the architecture of FTO/H2Chl-2 or ZnChl-2 on TiO2/(ZnChl-1)n/Ag were fabricated and the factors that presumably determine their photovoltaic performances were discussed. The photovoltaic devices studied herein employing inexpensive and pollution-free biomaterials provide a unique solution of utilizing solar energy with a care of the important environmental issue.

Carotenoids (Cars) and chlorophylls (Chls) are major pigments playing key roles in light-harvesting and energy transfer processes in natural photosynthetic apparatus. We demonstrated, in this study, photovoltaic cells with entire active layers consisting of a linear Car, lycopene, as the electron donor and Chl derivatives, either methyl 32,32-dicyano-pyropheophorbide-a (Chl-1) or methyl 131-deoxo-131-(dicyanomethylene)pyropheophorbide-a (Chl-2), as the electron acceptor.

In this study, we attempted to develop a protocol for fabricating efficient solid-state organic photovoltaics based on materials used currently for dye-sensitized solar cells. Three typical indoline dyes, namely, D131, D102, and D149, were employed as electron donors in conjunction with C70 fullerene in solution-processed planar-heterojunction (PHJ) organic solar cells (OSCs). The PHJ cells based on these dyes exhibited similar external quantum efficiencies over the entire spectral range, resulting in identical short-circuit photocurrents. The open-circuit voltages of the PHJ cells were consistent with the highest occupied molecular orbital level of the corresponding indoline dye. The D102-based PHJ cell exhibited the highest power conversion efficiency, of up to 3.1%. The efficiency was limited by the light-harvesting capability of the solar cell, given that the short diffusion length (∼5 nm) of D102 limited the thickness of the active layer; the diffusion length was determined through an optical simulation. The methyl ester of D102 (D102-Me) was synthesized to reduce the degree of intermolecular hydrogen bonding between the dye molecules. D102-Me was found to be more suited for use in OSCs fabricated by the thermal evaporation method. PHJ cells based on solution-processed and thermally evaporated active layers of D102-Me exhibited similar photovoltaic performances. However, in the case of D102, the device with the thermally evaporated layer exhibited lower performance than that of the device with the solution-processed layer, owing to the decomposition of D102 during the evaporation process. D102-Me was then co-evaporated with C70 in bulk-heterojunction OSCs. A power conversion efficiency as high as 5.1% could be achieved by optimizing this active layer; the D102-Me/C70 blend ratio in the optimized layer was 1:9, and the thickness of the layer was 70 nm.

Although ZnO is a compatible electron transport layer (ETL) for perovskite solar cells (PSCs), the fact that MAPbI3 easily undergoes thermal decomposition on a low-temperature processed ZnO surface limits the use of one-step deposition of perovskite and hence the resulting photovoltaic performance. Herein, we demonstrate triple cation perovskite (Csx(MA0.17FA0.83)(100−x)Pb(I0.83Br0.17)3) prepared with a one-step deposition method as a stable light absorber in highly efficient PSCs with low-temperature processed ZnO as the ETL. The photovoltaic performance of the investigated PSCs was dependent on both the annealing temperature of the perovskite film and the composition of the Cs element in the perovskite structure. A remnant PbI2 passivation phase in the perovskite layer, in which the composition is Cs6(MA0.17FA0.83)94Pb(I0.83Br0.17)3 and the annealing temperature is 95 °C, leads to the highest power conversion efficiency of ∼18.9%, which is a record-high so far for low-temperature processed ZnO-based PSCs. Importantly, this PSC exhibits excellent environmental durability and photostability, which are critical characteristics for further commercialization of low-temperature processed PSCs.

Despite the potential of ZnO as the electron collection material for low-temperature processed perovskite solar cells (PSCs), previous investigations revealed that the CH3NH3PbI3-based perovskite rapidly decomposes on ZnO at elevated temperature through a deprotonation process (base-induced reaction) that reduces thermal stability. To solve this thermal instability issue and to further enhance the photovoltaic performance, we employed a (FA)-based perovskite, i.e., FAPbI3 as the light absorber in ZnO-based PSCs. The photovoltaic performance of the investigated FAPbI3 solar cells was clearly dependent on both the pre-heating of the PbI2 precursor and post-annealing of the FAPbI3 film in the solar cell fabrication procedure. The highest power conversion efficiency of up to 16.1% was achieved under AM 1.5 simulated sunlight illumination, in which the pre-heating and post-annealing temperatures were 100 °C and 145 °C, respectively. Importantly, the thermostability of the perovskite film on ZnO was substantially improved with FAPbI3 owing to basically the robust nature of FA compared with methylammonium (MA) in CH3NH3PbI3. Moreover, FAPbI3-based PSCs exhibited excellent photostability and small J–V hysteresis, which are all useful characteristics for further commercialization of low-temperature processed ZnO solar cells.

We demonstrated SnO2 films prepared by sinter-less spin-coating processes as an electron selective contact for CH3NH3PbI3-based planar-heterojunction perovskite solar cells (PSCs). A modified sequential deposition method, in which the grain size of PbI2 precursors was controlled by an equivalent solvent vapor annealing (SVA) process, was used to prepare the perovskite layer on SnO2. With this SVA process, the remnant PbI2 nanocrystals can stably occur at the interface of CH3NH3PbI3/SnO2 to carry out a passivation effect. The photovoltaic performance of SnO2-based PSCs is dependent on both the SVA time and the thickness of the perovskite layer. The optimized PSC device achieves the best power conversion efficiency of up to 13% under the AM 1.5 simulated sunlight illumination, which is highly durable over 30 days of storage time with exposure to the ambient air environment.