Chin Hoong Teh

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

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 Mini Review: Can Graphene Be a Novel Material for Perovskite Solar Cell Applications?

Perovskite solar cells (PSCs) have raised research interest in scientific community because their power conversion efficiency is comparable to that of traditional commercial solar cells (i.e., amorphous Si, GaAs, and CdTe). Apart from that, PSCs are lightweight, are flexible, and have low production costs. Recently, graphene has been used as a novel material for PSC applications due to its excellent optical, electrical, and mechanical properties. The hydrophobic nature of graphene surface can provide protection against air moisture from the surrounding medium, which can improve the lifetime of devices. Herein, we review recent developments in the use of graphene for PSC applications as a conductive electrode, carrier transporting material, and stabilizer material. By exploring the application of graphene in PSCs, a new class of strategies can be developed to improve the device performance and stability before it can be commercialized in the photovoltaic market in the near future.

The architecture of the electron transport layer for a perovskite solar cell

The emergence of perovskite solar cells (PSCs) recently has brought new hope to the solar cell industry due to their incredible improvement of the power conversion efficiency (PCE), which can now exceed 20.0% within seven years of tremendous research. The efficiency and stability of PSCs depend strongly on the morphology and type of materials selected as the electron transport layer (ETL) in the device. In this review, the functions of the ETL based on titania (TiO2) in n–i–p architecture PSCs, including planar heterojunction and mesoporous-structured devices, are reviewed in terms of the device performance and stability. Studies found that the application of suitable fabrication techniques and manipulation of the nanostructural properties of TiO2 are crucial factors in ameliorating the short-circuit current density, JSC, and fill factor, FF, of PSCs. On top of that, the effect of substituting TiO2 with other potential inorganic materials like zinc oxide (ZnO), tin oxide (SnO2), ternary metal oxides, and metal sulphides, as well as organic semiconductors including fullerene, graphene, and ionic liquids, towards the photovoltaic properties and stability of the devices are also elaborated and discussed. Meanwhile, the utilization of non-electron transport layers (non-ETLs), such as alumina (Al2O3) and zirconia (ZrO2), as the mesoporous scaffold in PSCs is found to enhance the open-circuit voltage, VOC, of the devices.

2,2′-[2,5-Bis(hex­yloxy)-1,4-phenyl­ene]dithio­phene

The asymmetric unit of the title compound, C26H34O2S2, comprises one half-molecule located on an inversion centre. The thiophene groups are twisted relative to the benzene ring, making a dihedral angle of 5.30 (7)°, and the n-hexyl groups are in a fully extended conformation. In the crystal, there are short C—H⋯π contacts involving the thiophene groups.

Synthesis and characterization of 2,2′-bithiophene end-capped dihexyloxy phenylene pentamer and its application in a solution-processed organic ultraviolet photodetector

In this work a new solution processable small organic material, namely 2,2′-bithiophene end-capped dihexyloxy phenylene pentamer (BHBT2) was synthesized, characterized and applied in the fabrication of an organic ultraviolet photodetector. The material was synthesized via Williamson etherification, bromination and Suzuki coupling. FTIR and NMR spectroscopies were recorded for BHBT2 along with its optical, thermal and electrochemical properties. Finally, BHBT2 was used as donor material to produce a solution-processed UV photodetector based on a BHBT2 : PC61BM organic active layer. Results showed that in forward biasing, the photodetector exhibited a photovoltaic effect with Jsc = 1.80 mA, Voc = 0.66 V, FF = 0.30 and PCE = 0.98%, while in reverse biasing, the photodetector exhibited a fast, reversible and stable response with the highest detectivity of 1.47 × 109 jones. The realization of efficient UV detection was attributed to the strong absorption of BHBT2 and PC61BM in the UV region. Hence, the BHBT2 pentamer coupled with PC61BM can be considered as a potential material to be applied in a solution-processed organic UV photodetector.

3,5-Dibromo-2-[2,5-dibut-oxy-4-(3,5-dibromo-thio-phen-2-yl)phen-yl]thio-phene.

The title molecule, C22H22Br4O2S2, is centrosymmetric with an inversion centre located at the centre of the benzene ring. The 3,5-dibromothiophene groups are twisted relative to the benzene ring, making a dihedral angle of 41.43 (9)°.