Chun-Guey Wu

Highly Efficient Light-Harvesting Ruthenium Sensitizer for Thin-Film Dye-Sensitized Solar Cells

A high molar extinction coefficient heteroleptic ruthenium complex, incorporating an electron-rich hexylthio-terminal chain, has been synthesized and demonstrated as an efficient sensitizer for dye-sensitized solar cells. With this new sensitizer excellent power conversion efficiency is 11.5% and 4.7% obtained under an irradiation of full sunlight (air mass 1.5 global) in combination with a volatility electrolyte and solid state hole transporting material, respectively. The devices with low volatility electrolyte showed good stability under visible-light soaking at 60 degrees C during 1000 h of accelerated tests.

High efficiency stable inverted perovskite solar cells without current hysteresis

The inverted perovskite solar cell fabricated using a two-step method exhibited the highest FF of 0.85 and good efficiency of 18% based on CH3NH3PbI3. A small amount of H2O was added into PbI2/DMF to make a homogenous precursor solution. A high quality PbI2 film with full coverage was formed on a PEDOT:PSS surface by spin coating of the homogeneous PbI2 precursor solution. The perovskite film fabricated from the high quality PbI2 film is highly pure, smooth and very dense even without any pinhole. The champion cell achieves a remarkable fill factor (FF) of 0.85, which is the highest value reported in perovskite solar cells. The FF value is also very reproducible with less than 10% deviation for 50 cells. The cell exhibits no current hysteresis and is stable under both dark and illumination conditions in dry and inert atmospheres. The results not only provide a strategy to fabricate high efficiency inverted perovskite solar cells but also reveal how the water additive in the PbI2/DMF solution may affect the properties of PbI2 and therefore the perovskite film prepared using the two-step method and the overall photovoltaic performance of the corresponding inverted solar cell.

Planar heterojunction perovskite/PC71BM solar cells with enhanced open-circuit voltage via a (2/1)-step spin-coating process

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%.

The synergistic effect of H2O and DMF towards stable and 20% efficiency inverted perovskite solar cells

A high quality thick (500 nm) CH3NH3PbI3 perovskite absorber with a horizontal grain size up to 3 μm and a lateral size equal to the film thickness was prepared by the synergistic effect of a H2O additive and DMF vapor treatment via a two-step spin coating method. The inverted (p–i–n) cell based on this high-quality thick perovskite film achieves a high power conversion efficiency of 20.1%. The cell shows no current hysteresis and is stable in inert and ambient atmospheres with appropriate encapsulation. H2O helps MAI to penetrate into the thick PbI2 to form a thick film with a pure MAPbI3 phase and produces bigger gains by slowing down the perovskite crystallization rate. It can also cooperate with DMF to control the dissolution of perovskite grains during DMF vapor post treatment. As a result, large multi-crystalline perovskite grains without observable holes and creases are formed when DMF and H2O were removed during the following heating process. The synergistic effect of H2O and DMF was evidenced by SEM images and GIWXRD patterns taken simultaneously. This synergistic strategy for preparing a high-quality, thick perovskite film was extended to fabricate a large-area MAPbI3 film (1.3 cm2 and 11.25 cm2 for the cell and mini-module, respectively) to realize an efficiency of 16.7 and 15.4%.

Unsymmetrical squaraines incorporating the thiophene unit for panchromatic dye-sensitized solar cells.

Two unsymmetrical squaraines, where the electron-rich 3,4-ethylenedioxythiophene or bithiophene conjugated fragment was used to link unconventionally the squaraine core and the hexyloxyphenyl amino group, were applied for DSCs. The corresponding photovoltaic devices exhibit an attractively panchromatic response and also convert a portion of the near-infrared photons into electricity.

Surface Engineering of ZnO Thin Film for High Efficiency Planar Perovskite Solar Cells.

Sputtering made ZnO thin film was used as an electron-transport layer in a regular planar perovskite solar cell based on high quality CH3NH3PbI3 absorber prepared with a two-step spin-coating. An efficiency up to 15.9% under AM 1.5G irradiation is achieved for the cell based on ZnO film fabricated under Ar working gas. The atmosphere of the sputtering chamber can tune the surface electronic properties (band structure) of the resulting ZnO thin film and therefore the photovoltaic performance of the corresponding perovskite solar cell. Precise surface engineering of ZnO thin film was found to be one of the key steps to fabricate ZnO based regular planar perovskite solar cell with high power conversion efficiency. Sputtering method is proved to be one of the excellent techniques to prepare ZnO thin film with controllable properties.

Efficient and stable plastic dye-sensitized solar cells based on a high light-harvesting ruthenium sensitizer

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 TiO2 paste 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 TiO2 thin 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-E1 dye 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.

A composite catalytic film of PEDOT:PSS/TiN–NPs on a flexible counter-electrode substrate for a dye-sensitized solar cell

A composite film of PEDOT:PSS/TiN–NPs, containing poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and titanium nitride nanoparticles (TiN–NPs), was deposited on a Ti foil by a doctor blade technique. Various weight percentages of TiN–NPs (5, 10, 20, 30 wt%) were used to prepare different composite films. This Ti foil with the composite film was used as the flexible counter-electrode (CE) for a dye-sensitized solar cell (DSSC). Performances of the DSSCs with the platinum-free CEs containing PEDOT:PSS/TiN–NPs with various contents of TiN–NPs were investigated. After the optimization of composition and thickness of the composite film PEDOT:PSS/TiN–NPs, a light-to-electricity conversion efficiency (η) of 6.67% was achieved for the pertinent DSSC, using our synthesized CYC-B1 dye, which was found to be higher than that of a cell with a sputtered-Pt film on its CE (6.57%). The homogeneous nature of the composite film PEDOT:PSS/TiN–NPs, the uniform distribution of TiN–NPs in its polymer matrix, and the large electrochemical surface area of the composite film are seen to be the factors for the best performance of the pertinent DSSC. Scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and energy dispersive X-ray spectroscopy (EDX) were used to characterize the films. The high efficiency of the cell with PEDOT:PSS/TiN–NPs is explained by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and incident photon-to-current conversion efficiency (IPCE) curves.

Heteroleptic ruthenium antenna-dye for high-voltage dye-sensitized solar cells

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 × 104 M−1 cm−1. In addition, a simple approach to reduce the aggregation of bulky ruthenium dyes assembled onto the surface of TiO2 film is demonstrated. The cell based on this new heteroleptic ruthenium dye provides a high Voc of 788 mV and an overall conversion efficiency (η) of 8.96%. The functionality of carbazole in CYC-B7 resulting in the increases of the Voc value of the corresponding device is verified by comparing with the performance of the DSC sensitized with a structurally similar dye without carbazole.

Efficient ternary bulk heterojunction solar cells based on small molecules only

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.