Probing the Optical Property and Electronic Structure of TiO2 Nanomaterials for Renewable Energy Applications

This review summarizes the current designs and development of new types of organic small molecules as a hole-transporting material (HTM) in a meso-structured perovskite solar cell (PSC). The roles of each layer in the meso-structured perovskite device architecture are elaborated and the employment of new types of organic HTMs in the device is compared with the commercially available HTM spiro-OMeTAD in terms of the properties, device performance and stability. The studies found that nearly half of the new synthesized and pristine HTMs have comparable or better photovoltaic properties than those of doped spiro-OMeTAD. These HTMs have the characteristics of a fused planar core structure with extended π-conjugated lengths and electron-donating functional groups, which are believed to contribute to their high intrinsic conductivity and help make them an alternative to spiro-OMeTAD as a better HTM in meso-structured PSCs. Some of the devices based on the new synthesized HTMs even have longer device lifetimes than their spiro-OMeTAD-based PSC counterparts. Moreover, studies found that the cost per gram (Cg) and cost-per-peak Watt (Cw) of synthesized HTMs can be reduced via minimizing the number of synthesis steps and by optimization of the starting materials in order to yield low-cost HTMs for meso-structured PSC applications.

A review of organic small molecule-based hole-transporting materials for meso-structured organic-inorganic perovskite solar cells

A new type of hole transporting material (HTMs) with an incorporated planar amine or triphenylamine as a core unit have been prepared. The two amine derivatives were demonstrated to be efficient hole transporting materials in fabricating solid-state organic-inorganic hybrid solar cells. Perovskite-based solar cells with a planar amine derivative gave a short circuit photocurrent density (J(sc)) of 20.98 mAcm(-2), an open circuit voltage (V-oc) of 0.972 V, and a fill factor of 0.67, corresponding to an overall conversion efficiency of 13.63 %. The photovoltaic performance is comparable to that of the standard spiro-OMeTAD. Moreover, the device showed good stability under light soaking for 500 h. These HTMs hold promise to replace the expensive spiro-OMeTAD because of their high efficiency, excellent stability, synthesis from simple and inexpensive materials.

Efficient Perovskite Solar Cells with 13.63 % Efficiency Based on Planar Triphenylamine Hole Conductors

Dye-sensitized solar cells (DSSCs) have aroused great interest and been regarded as a potential renewable energy resource among the third-generation solar cell technologies to fulfill the 21st century global energy demand. DSSCs have notable advantages such as low cost, easy fabrication process and being eco-friendly in nature. The progress of DSSCs over the last 20 years has been nearly constant due to some limitations, like poor long-term stability, narrow absorption spectrum, charge carrier transportation and collection losses and poor charge transfer mechanism for regeneration of dye molecules. The main challenge for the scientific community is to improve the performance of DSSCs by using different approaches, like finding new electrode materials with suitable nanoarchitectures, dyes in composition with promising semiconductors and metal quantum dot fluorescent dyes, and cost-effective hole transporting materials (HTMs). This review focuses on DSSC photo-physics, which includes charge separation, effective transportation, collection and recombination processes. Different nanostructured materials, including metal oxides, oxide perovskites and carbon-based composites, have been studied for photoanodes, and counter electrodes, which are crucial to achieve DSSC devices with higher efficiency and better stability.

Nanoarchitectures in dye-sensitized solar cells: metal oxides, oxide perovskites and carbon-based materials

New organic dyes containing fluorene functionalized with two imidazole chromophores as donors and cyanoacrylic acid acceptors have been synthesized and successfully demonstrated as sensitizers in nanocrystalline TiO2-based dye-sensitized solar cells (DSSCs). The monoimidazole analogues were also synthesized for comparison. The Sommelet reaction of bromomethylated 2-bromo-9,9-diethyl-9H-fluorene produced the key precursor 7-bromo-9,9-diethyl-9H-fluorene-2,4-dicarbaldehyde required for the preparation of imidazole-functionalized fluorenes. Since the dyes possess weak donor segment, the electron-richness of the conjugation pathway dictated the optical, electrochemical, and photovoltaic properties of the dyes. The dyes served as sensitizers in DSSC and exhibited moderate efficiency up to 3.44%. The additional imidazole present on the fluorene has been found to retard the electron recombination due to the bulkier hydrophobic environment and led to high open-circuit voltage in the devices.

Organic Dyes Containing Fluorene Decorated with Imidazole Units for Dye-Sensitized Solar Cells

Although numerous donor-π-acceptor (D-π-A) type organic dyes were investigated in order to replace the ruthenium polypyridyl complexes, there have been few reports of the D-π-2A system and the related electron transfer processes. In this work, a novel D-π-2A dye (coded as B2) was designed and synthesized for applications in dye-sensitized solar cells (DSSC). Obvious intramolecular charge transfer (ICT) between the donor and acceptor takes place under photoexcitation. Three frontier LUMOs (LUMO, LUMO+1, LUMO+2) of B2 are all located on the acceptor part, which is highly favorable for intramolecular electron transfer from the donor to acceptors and enhances the electron injection into the semiconductors. DSSC based on B2 showed a maximum monochromatic incident photon-to-current efficiency (IPCE) of 68% at 425 nm and an overall power conversion efficiency of 3.62% under simulated solar light (AM 1.5G, 100 mW cm–2) irradiation. Femtosecond and nanosecond TA, and TCSPC techniques were used to monitor the photo...

Bin Tong

Papers

Novel Organic D-π-2A Sensitizer for Dye Sensitized Solar Cells and Its Electron Transfer Kinetics on TiO2 Surface