Tungsten oxide ͑WO 3 ͒ was inserted as an anode interfacial layer between the photoactive layer and top electrode in inverted polymer solar cells ͑PSCs͒ with nanocrystalline titanium dioxide as an electron selective layer. The device with WO 3 exhibited a remarkable improvement in power conversion efficiency compared with that without WO 3 , which indicated that WO 3 efficiently prevented the recombination of charge carriers at the organic/top electrode interface. The dependence of the device performances on WO 3 film thickness and different top metal electrodes was investigated. Transparent inverted PSCs with thermally evaporable Ag/ WO 3 as a transparent anode were also investigated when introducing a WO 3 buffer layer.
Semitransparent inverted polymer solar cells were developed using thermally evaporable MoO3/Ag/MoO3 as transparent anode. The ultrathin inner MoO3 layer was introduced as a buffer layer to improve hole collection, while the outer MoO3 layer served as a light coupling layer to enhance optical transmittance of the device. The dependence of the device performances on the thickness of the outer MoO3 layer was investigated. The results showed that the addition of the outer MoO3 layer improves the transmittance of the anode compared to MoO3/Ag anode and the performances of the semitransparent devices with the outer MoO3 layer are improved due to the reduced series resistance.
Molybdenum disulfide (MoS2) is considered as a promising 2D material for optoelectronic applications due to its excellent electrical and optical properties. A semimetal material with zero bandgap, like graphene, can extend response range of MoS2‐based photodetectors to wider spectral region. Here, a graphene/MoS2/graphene vertical heterostructure is demonstrated, where Schottky barriers are formed between MoS2 and graphenes. The introduction of graphene can effectively widen the working wavelength of the device from visible to IR range. Simultaneously, the shortened transmit distance for the photogenerated carriers between the source and drain electrodes in the vertical heterostructure leads to faster response speed compared with MoS2‐based photodetectors. Besides, the graphene/MoS2/graphene photodetector shows excellent performance with an enhanced responsivity of 414 A W−1 at 532 nm and 376 A W−1 at 2000 nm, and a broad working wavelength ranging from 405 to 2000 nm. These excellent performances prove that the design of graphene based vertical heterostructure can provide new ideas for the development of high‐performance photodetectors in future.
Two-dimensional (2D) indium selenide (InSe) has been widely studied for applications in transistors and photodetectors, benefitting from its excellent optoelectronic properties. Among the three specific polytypes (γ-, ϵ- and β-phase) of InSe, only the crystal lattice of InSe in β-phase (β-InSe) belongs to a nonsymmetry point group of $D_{6h}^4$, which indicates a stronger anisotropic transport behavior and a potential in the polarized photodetection of β-InSe based optoelectronic devices. Therefore, we prepare the stable p-type 2D layered β-InSe via temperature gradient method. The anisotropic Raman, transport and photoresponse properties of β-InSe have been experimentally and theoretically proved. It shows that the β-InSe based device has a ratio of 3.76 for the maximum to minimum dark current and a high photocurrent anisotropic ratio of 0.70 at 1 V bias voltage, respectively. The appealing anisotropic properties demonstrated in this work clearly identify β-InSe as a competitive candidate for filter-free polarization sensitive photodetectors.
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