Study of Quantum Dot/Inorganic Layer/Dye Molecule Sandwich Structure for Electrochemical Solar Cells

A highly efficient quantum dot (QD)/inorganic layer/dye molecule sandwich structure was designed and applied in electrochemical QD-sensitized solar cells. The key component TiO₂/CdS/ZnS/N719 hybrid photoanode with ZnS insertion between the two types of sensitizers was demonstrated not only to efficiently extend the light absorption but also to suppress the charge recombination from either TiO₂ or CdS QDs to electrolyte redox species, yielding a photocurrent density of 11.04 mA cm^–2, an open-circuit voltage of 713 mV, a fill factor of 0.559, and an impressive overall energy conversion efficiency of 4.4%. More importantly, the cell exhibited enhanced photostability with the help of the synergistic stabilizing effect of both the organic and the inorganic passivation layers in the presence of a corrosive electrolyte

Efficient Light Harvesting and Charge Collection of Dye-Sensitized Solar Cells with (001) Faceted Single Crystalline Anatase Nanoparticles

With a comparable specific surface area, 17% enhanced dye-loading capacity was observed for the first time in the (001) faceted TiO₂ single crystals compared to that of benchmark P25 nanoparticles, thus generating a significant enrichment in both short-circuit photocurrent density and power conversion efficiency of dye-sensitized solar cells (DSCs). Such a remarkably increased dye-loading capacity was primarily ascribed to the higher density of 5-fold-coordinnated Ti atoms on the (001) surfaces. Furthermore, kinetic studies revealed that such single crystals confer a higher electron lifetime and charge collection efficiency compared with conventional P25 electrode, which might originate from the specific surface configuration in these high energetic facet dominant single crystals. Our study provides straightforward evidence for the superior reactivity of (001) facets and implies that such single TiO₂ crystals with high-energetic facets would be a promising electrode material for DSCs

Working from Both Sides: Composite Metallic Semitransparent Top Electrode for High Performance Perovskite Solar Cells

We report herein perovskite solar cells using solution-processed silver nanowires (AgNWs) as transparent top electrode with markedly enhanced device performance, as well as stability by evaporating an ultrathin transparent Au (UTA) layer beneath the spin-coated AgNWs forming a composite transparent metallic electrode. The interlayer serves as a physical separation sandwiched in between the perovskite/hole transporting material (HTM) active layer and the halide-reactive AgNWs top-electrode to prevent undesired electrode degradation and simultaneously functions to significantly promote ohmic contact. The as-fabricated semitransparent PSCs feature a <i>V</i>_oc of 0.96 V, a <i>J</i>_sc of 20.47 mA cm^–2, with an overall PCE of over 11% when measured with front illumination and a <i>V</i>_oc of 0.92 V, a <i>J</i>sc of 14.29 mA cm^–2, and an overall PCE of 7.53% with back illumination, corresponding to approximately 70% of the value under normal illumination conditions. The devices also demonstrate exceptional fabrication repeatability and air stability

Aluminum-Doped Zinc Oxide as Highly Stable Electron Collection Layer for Perovskite Solar Cells

Although low-temperature, solution-processed zinc oxide (ZnO) has been widely adopted as the electron collection layer (ECL) in perovskite solar cells (PSCs) because of its simple synthesis and excellent electrical properties such as high charge mobility, the thermal stability of the perovskite films deposited atop ZnO layer remains as a major issue. Herein, we addressed this problem by employing aluminum-doped zinc oxide (AZO) as the ECL and obtained extraordinarily thermally stable perovskite layers. The improvement of the thermal stability was ascribed to diminish of the Lewis acid–base chemical reaction between perovskite and ECL. Notably, the outstanding transmittance and conductivity also render AZO layer as an ideal candidate for transparent conductive electrodes, which enables a simplified cell structure featuring glass/AZO/perovskite/Spiro-OMeTAD/Au. Optimization of the perovskite layer leads to an excellent and repeatable photovoltaic performance, with the champion cell exhibiting an open-circuit voltage (<i>V</i>_oc) of 0.94 V, a short-circuit current (<i>J</i>_sc) of 20.2 mA cm^–2, a fill factor (FF) of 0.67, and an overall power conversion efficiency (PCE) of 12.6% under standard 1 sun illumination. It was also revealed by steady-state and time-resolved photoluminescence that the AZO/perovskite interface resulted in less quenching than that between perovskite and hole transport material

Kinetics versus Energetics in Dye-Sensitized Solar Cells Based on an Ethynyl-Linked Porphyrin Heterodimer

Out of the scientific concern on the kinetics versus energetics for rational understanding and optimization of near-IR dye-sensitized solar cells (DSCs), an <i>N</i>-fused carbazole-substituted ethynyl-linked porphyrin heterodimer (<b>DTBC</b>) reported previously by our group was focused upon in terms of photovoltaic, photoelectrochemical, and steady-state and time-resolved photophysical properties in varied electrolyte environments. A primitive attempt to balance the photocurrent against the photovoltage by varying the concentration of the common coadsorbent 4-<i>tert</i>-butylpyridine (TBP) revealed that TBP continuously suppressed injection but provided inadequate compensation in open-circuit voltage (<i>V</i>_oc). This further drew out the perspective of the widely ignored dye–electrolyte interaction in DSCs, specifically the axial coordination of TBP to the central zinc cation in porphyrin sensitizers that may retard electron injection. As an alternative, a TBP-free electrolyte containing guanidinium thiocyanate was developed to realize greatly promoted <i>V</i>_oc with little current sacrifice, thus significantly enhancing overall energy conversion efficiencies. The excited state was protracted to counteract the injection retardation caused by much reduced driving force, setting a successful example of bilateral compromise between kinetics and energetics in near-IR DSCs

GaNb₁₁O₂₉ Nanowebs as High-Performance Anode Materials for Lithium-Ion Batteries

M–Nb–O compounds have been considered as promising anode materials for lithium-ion batteries (LIBs) because of their high capacities, safety, and cyclic stability. However, very limited M–Nb–O anode materials have been developed thus far. Herein, GaNb₁₁O₂₉ with a shear ReO₃ crystal structure and a high theoretical capacity of 379 mAh g^–1 is intensively explored as a new member in the M–Nb–O family. GaNb₁₁O₂₉ nanowebs (GaNb₁₁O₂₉-N) are synthesized based on a facile single-spinneret electrospinning technique for the first time and are constructed by interconnected GaNb₁₁O₂₉ nanowires with an average diameter of ∼250 nm and a large specific surface area of 10.26 m² g^–1. This intriguing architecture affords good structural stability, restricted self-aggregation, a large electrochemical reaction area, and fast electron/Li⁺-ion transport, leading to a significant pseudocapacitive behavior and outstanding electrochemical properties of GaNb₁₁O₂₉–N. At 0.1 C, it shows a high specific capacity (264 mAh g^–1) with a safe working potential (1.69 V vs Li/Li⁺) and the highest first-cycle Coulombic efficiency in all of the known M–Nb–O anode materials (96.5%). At 10 C, it exhibits a superior rate capability (a high capacity of 175 mAh g^–1) and a durable cyclic stability (a high capacity retention of 87.4% after 1000 cycles). These impressive results indicate that GaNb₁₁O₂₉-N is a high-performance anode material for LIBs

High Efficiency Inverted Planar Perovskite Solar Cells with Solution-Processed NiO_<i>x</i> Hole Contact

NiO_<i>x</i> is a promising hole-transporting material for perovskite solar cells due to its high hole mobility, good stability, and easy processability. In this work, we employed a simple solution-processed NiO_<i>x</i> film as the hole-transporting layer in perovskite solar cells. When the thickness of the perovskite layer increased from 270 to 380 nm, the light absorption and photogenerated carrier density were enhanced and the transporting distance of electron and hole would also increase at the same time, resulting in a large charge transfer resistance and a long hole-extracted process in the device, characterized by the UV–vis, photoluminescence, and electrochemical impedance spectroscopy spectra. Combining both of these factors, an optimal thickness of 334.2 nm was prepared with the perovskite precursor concentration of 1.35 M. Moreover, the optimal device fabrication conditions were further achieved by optimizing the thickness of NiO_<i>x</i> hole-transporting layer and PCBM electron selective layer. As a result, the best power conversion efficiency of 15.71% was obtained with a <i>J</i>_sc of 20.51 mA·cm^–2, a <i>V</i>_oc of 988 mV, and a FF of 77.51% with almost no hysteresis. A stable efficiency of 15.10% was caught at the maximum power point. This work provides a promising route to achieve higher efficiency perovskite solar cells based on NiO or other inorganic hole-transporting materials