Tzu-Yen Huang

Synergistic improvements in stability and performance of lead iodide perovskite solar cells incorporating salt additives

The main issues in planar perovskite solar cells are the coverage and crystallinity of the perovskite film on the PEDOT:PSS layer. To enhance these features, we introduced alkali metal halides (salts) as additives into the perovskite precursor solution used in a two-step preparation method. These alkali metal halides chelate with Pb2+ ions and enhance the crystal growth of PbI2 films, resulting in nanostructured morphologies. The nanostructured PbI2 films promote homogeneous nucleation and larger crystallite sizes, thereby enhancing the morphology and crystallinity of the perovskite films. The alkali metal halides recrystallize the small grains and passivate the grain boundaries and interface states, allowing effective charge generation and dissociation in perovskite films. Photoluminescence measurements indicated that perovskite films prepared with salt additives featured fewer charge traps and defects. The power conversion efficiency of the device incorporating a small amount of a salt additive increased by approximately 33%—from 11.4 to 15.08%. This device was more stable than a corresponding device prepared without the additive, with only 16.5% degradation occurring over a period of 50 days.

2-Alkyl-5-thienyl-Substituted Benzo[1,2-b:4,5-b′]dithiophene-Based Donor Molecules for Solution-Processed Organic Solar Cells

In this study, we have strategically designed and convergently synthesized two novel, symmetrical, and linear A-D-A-type π-conjugated donor molecules (TBDTCNR, TBDTCN), each containing a planar electron-rich 2-octylthiene-5-yl-substituted benzodithiophene (TBDT) unit as the core, flanked by octylthiophene units and end-capped with electron-deficient cyanoacetate (CNR) or dicyanovinyl (CN) units. We thoroughly characterized both of these materials and investigated the effects of the end groups (CNR, CN) on their optical, electrochemical, morphological, and photovoltaic properties. We then fabricated solution-processed bulk heterojunction organic solar cells incorporating TBDTCNR and TBDTCN. Among our tested devices, the one containing TBDTCNR and [6,6]-phenyl-C61-butyric acid methyl ester in a 1:0.40 ratio (w/w) exhibited the highest power conversion efficiency (5.42%) with a short-circuit current density (Jsc) of 9.08 mA cm(-2), an open circuit voltage (Voc) of 0.90 V, and an impressive fill factor (FF) of 0.66 under AM 1.5G irradiation (100 mW cm(-2)). The FFs of these solution-processed small-molecule organic solar cells (SMOSCs) are outstanding when compared with those recently reported for benzodithiophene (BDT)-based SMOSCs, because of the high crystallinity and excellent stacking properties of the TBDT-based compounds.

Using an Airbrush Pen for Layer-by-Layer Growth of Continuous Perovskite Thin Films for Hybrid Solar Cells

In this manuscript we describe hybrid heterojunction solar cells, having the device architecture glass/indium tin oxide/poly(3,4-ethylenedioxythiopene)/poly(styrenesulfonic acid)/perovskite/[6,6]-phenyl-C61-butyric acid methyl ester/C60/2,9-dimethyl- 4,7-diphenyl-1,10-phenanthroline/Al, fabricated using lead halide perovskite obtained through spray-coating at a low precursor concentration. To study the relationship between the morphology and device performance, we recorded scanning electron microscopy images of perovskite films prepared at various precursor ratios, spray volumes, substrate temperatures, and postspray annealing temperatures. Optimization of the spray conditions ensured uniform film growth and high surface area coverage at low substrate temperatures. Lead halide perovskite solar cells prepared under the optimal conditions displayed an average power conversion efficiency (PCE) of approximately 9.2%, with 85% of such devices having efficiencies of greater than 8.3%. The best-performing device exhibited a short-circuit current density of 17.3 mA cm(-2), a fill factor of 0.63, and an open-circuit voltage of 0.93 V, resulting in a PCE of 10.2%. Because spray-coating technology allows large-area deposition, we also fabricated devices having areas of 60 and 342 mm(2), achieving PCEs with these devices of 6.88 and 4.66%, respectively.

rGO/SWCNT composites as novel electrode materials for electrochemical biosensing

In this study we performed electrochemical sensing using conductive carbon composite films containing reduced graphene oxide (rGO) and single-walled carbon nanotubes (SWCNTs) as electrode modifiers on glassy carbon electrodes (GCEs). Raman spectroscopy, transmission electron microscopy, atomic force microscopy, and scanning electron microscopy all suggested that the rGO acted as a surfactant, covering and smoothing out the surface, and that the SWCNTs acted as a conducting bridge to connect the isolated rGO sheets, thereby (i) minimizing the barrier for charge transfer between the rGO sheets and (ii) increasing the conductivity of the film. We used the rGO/SWCNT-modified GCE as a sensor to analyze hydrogen peroxide (H2O2) and β-nicotinamide adenine dinucleotide (NADH), obtaining substantial improvements in electrochemical reactivity and detection limits relative to those obtained from rGO- and SWCNT-modified electrodes, presumably because of the higher conductivity and greater coverage on the GCE, due to π-π interactions originating from the graphitic structures of the rGO and SWCNTs. The electrocatalysis response was measured by cyclic voltammetry and amperometric current-time (i-t) curve techniques. The linear concentration range of H2O2 and NADH detection at rGO/SWCNT-modified electrode is 0.5-5M and 20-400μM. The sensitivity for H2O2 and NADH detection is 2732.4 and 204μAmM(-1)cm(-2), and the limit of detection is 1.3 and 0.078μM respectively. Furthermore, interference tests indicated that the carbon composite film exhibited high selectivity toward H2O2 and NADH. Using GO as a solubilizing agent for SWCNTs establishes a new class of carbon electrodes for electrochemical sensors.

Planar Heterojunction Perovskite Solar Cells Incorporating Metal–Organic Framework Nanocrystals

Zr-based porphyrin metal-organic framework (MOF-525) nanocrystals with a crystal size of about 140 nm are synthesized and incorporated into perovskite solar cells. The morphology and crystallinity of the perovskite thin film are enhanced since the micropores of MOF-525 allow the crystallization of perovskite to occur inside; this observation results in a higher cell efficiency of the obtained MOF/perovskite solar cell.

A high performance electrochemical sensor for acetaminophen based on a rGO–PEDOT nanotube composite modified electrode

In this study, we perform an electrochemical sensing using a conductive composite film containing reduced graphene oxide (rGO) and poly(3,4-ethylenedioxythiophene) nanotubes (PEDOT NTs) as an electrode modifier on a glassy carbon electrode (GCE). Scanning electron microscopy suggests that the rGO covers the surface of GCE uniformly and the PEDOT NTs act as a conducting bridge to connect the isolated rGO sheets. By combining these two materials, the conductivity and the surface coverage of the film can be enhanced, which is beneficial for electrochemical sensing. The rGO–PEDOT NT composite modified electrode is applied for an effective sensor to analyze acetaminophen. The obtained electrochemical activity is much higher than those obtained by the rGO- and PEDOT NT-modified electrodes; the higher electrochemical activity may be attributed to the higher conductivity and greater coverage of the rGO–PEDOT NT composite film on the GCE. Furthermore, interference tests indicate that the rGO–PEDOT NT composite modified electrode exhibits high selectivity toward the analyte. This novel method for combining the rGO and PEDOT NTs establishes a new class of carbon material-based electrodes for electrochemical sensors.

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.

Wet-milled transition metal oxide nanoparticles as buffer layers for bulk heterojunction solar cells

In this study, we used high-energy grinding to prepare solutions of well-dispersed transition metal oxides (TMOs), allowing the fabrication of crystalline TMO films with high surface coverage through solution processing without post-annealing. Moreover, because this solution-based method did not require surfactants, it preserved the intrinsic electronic and optical properties of the TMOs. The resulting smooth, continuous, and highly transparent TMO films were readily integrated into organic solar cells. After incorporating MoO3 thin films into bulk heterojunction solar cells, we obtained devices delivering power conversion efficiencies of up to 3.68%, rivalling those of devices fabricated with commercial poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) as the hole collection layer.

Efficiency Enhancement of Hybrid Perovskite Solar Cells with MEH-PPV Hole-Transporting Layers

In this study, hybrid perovskite solar cells are fabricated using poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and poly(3-hexylthiophene-2,5-diyl) (P3HT) as dopant-free hole-transporting materials (HTMs), and two solution processes (one- and two-step methods, respectively) for preparing methylammonium lead iodide perovskite. By optimizing the concentrations and solvents of MEH-PPV solutions, a power conversion efficiency of 9.65% with hysteresis-less performance is achieved, while the device with 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′spirobifluorene (Spiro-OMeTAD) doped with lithium salts and tert-butylpyridine (TBP) exhibits an efficiency of 13.38%. This result shows that non-doped MEH-PPV is a suitable, low-cost HTM for efficient polymer-based perovskite solar cells. The effect of different morphologies of methylammonium lead iodide perovskite on conversion efficiency is also investigated by incident photon-to-electron conversion efficiency (IPCE) curves and electrochemical impedance spectroscopy (EIS).

Enhanced Charge Collection in MOF-525–PEDOT Nanotube Composites Enable Highly Sensitive Biosensing

Abstract With the aim of a reliable biosensing exhibiting enhanced sensitivity and selectivity, this study demonstrates a dopamine (DA) sensor composed of conductive poly(3,4‐ethylenedioxythiophene) nanotubes (PEDOT NTs) conformally coated with porphyrin‐based metal–organic framework nanocrystals (MOF‐525). The MOF‐525 serves as an electrocatalytic surface, while the PEDOT NTs act as a charge collector to rapidly transport the electron from MOF nanocrystals. Bundles of these particles form a conductive interpenetrating network film that together: (i) improves charge transport pathways between the MOF‐525 regions and (ii) increases the electrochemical active sites of the film. The electrocatalytic response is measured by cyclic voltammetry and differential pulse voltammetry techniques, where the linear concentration range of DA detection is estimated to be 2 × 10−6–270 × 10−6 m and the detection limit is estimated to be 0.04 × 10−6 m with high selectivity toward DA. Additionally, a real‐time determination of DA released from living rat pheochromocytoma cells is realized. The combination of MOF5‐25 and PEDOT NTs creates a new generation of porous electrodes for highly efficient electrochemical biosensing.