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In this work, the impact of donor material on the optical and photodiode response is revealed by comparing the performance of self-powered photodiodes based on D:Alq3 (D=TPD or NPD) composite. The active layers were fabricated from solution-processed composites using the well-known spin coating technique, followed by their optical and electrical characterizations. The photodiodes were utilized for the UV light detection in a self-powered mode, in which no external power is required, but it is generated through the photovoltaic effect. Results showed that the NPD film has provided a broader and more intensive optical absorption towards the UV light compared to that of TPD. Also, photoluminescence quenching in the NPD:Alq3 composite was found to highly outperform that of the TPD:Alq3. These were ascribed to the effect of extra pi conjugated bonds present in the NPD, which are originated from the aromatic rings. Consequently, the NPD:Alq3 photodiodes presented a respective sensitivity, responsivity and detectivity of 1.3×105, 1.07 mA/W and 5.25×1011 Jones at 0 V. Moreover, the response (0.34 s) and recovery time (0.28 s) of these devices were found to be smaller compared to those reported in literature.

Herein, we report a novel self-powered photodiode, which is based on all solution-processed active layer made of bulk heterojunction of TPD:Alq3. The photodiodes can be utilized for the detection of ultraviolet (UV) radiation in a self-powered mode without the need for an external power supply. The optimized photodiode with TPD:Alq3 (1:2) active layer presented a sensitivity, responsivity and detectivity of 1.76 × 103, 5.22 × 10−4 A/W and 3.11 × 1010 Jones, respectively at zero biased mode under 365 nm UV light. We proposed a new approach of utilizing impedance matching to deliver the maximum power of photodiodes to the external load. Nevertheless, with a tool of minimized impedance, one can nearly get the full functionality of the photodiode at zero biased volt, but with zero power delivery to the tool. The performance of TPD:Alq3 based photodiodes outperformed that of photodiodes reported in literature.

This work reports a highly sensitive self-powered ultraviolet photodetector, which is based on the active layer of NPD:Alq3 with different Alq3 contents. All solution-processed technique was utilized to fabricate the active layers of the devices to achieve an optimized system that exhibits highly sensitive and stable photodetector under self-powered operation mode. The values of photosensitivity, responsivity, and detectivity of the photodiodes at zero-bias were estimated at 1.30 × 105, 1.07 mA/W, 1.04 × 1011 Jones, respectively. The rise and decay times of the optimized device were estimated at 0.34 s and 0.28 s, respectively. For practical application of the device sensing efficiency, the optimal load line of self-powered UV photodetector to deliver the maximum power was estimated of an internal impedence of 0.579 MΩ. In conclusion, the high sensitivity, good stability, and fast response/recovery speed of the self-powered UV photodetector make the devices applicable to resolve some of the current issues in UV detection.

In this work, a broad investigation on the optical parameters of TPD:Alq3 composite thin films is reported. The films are prepared from different solution-processed mixtures and are deposited onto the quartz substrate in order to measure their optical response with UV–Vis–NIR spectrophotometer. Results showed that the non-dispersive refractive index and dielectric constant of TPD was increased from 1.49 to 1.75 and from 2.19 to 2.99 by Alq3 doping, respectively. The optical conductivity of TPD:Alq3 (1:3) composite was seen to be highly improved, reaching the value of 144 S/cm. The Wemple and DiDomenico (WD) model was used to find the band gap ( E g W D ) of the films and results were compared to those deduced from the Tauc's equation ( E g o p t ). It was found that the investigated films obey the single-oscillator model in defining the strength of the optical transitions.

The optoelectronics and spectroscopic properties of N, N-diphenyl-N, N-bis(3-methylphenyl)-1, 1-biphenyl-4.4 diamine: tris (8-hydroxyquinolinate) aluminum (TPD:Alq3) systems were investigated for the application of ultraviolet (UV) sensors. Solution processed spin coating technique was used to deposit the films on quartz and to fabricate the devices on ITO-integrated substrates. Results showed that UV absorption of TPD was improved by its doping with Alq3 acceptor in a 1:2 volumetric ratio, thereby reducing its energy gap from 3.08 eV to 2.95 eV. The electronic transition in TDP was found to be direct forbidden, but changed to direct allowed transition by Alq3 dopant. Larger photocurrent, increased exciton generation and improved UV sensing was achieved for TPD:Alq3 (1:2) based UV detectors compared to that of the TPD-based devices. The signal to noise ratio was increased when Alq3 content was added up to 1:2 volumetric ratio, while it was decreased when higher amount of Alq3 was added.

In this paper, we present a visible-blind organic photodetector with high sensitivity to the UV rays. The active layer is a bulk heterojunction of a binary blend of tris(8-hydroxyquinoline) aluminum (Alq3) as an acceptor material along with N, N′-Di [(1-naphthyl)-N, N′- diphenyl]-(1, 1′-biphenyl)-4, 4′-diamine (NPD) as a donor material. The device was fabricated using simple solution processing method with structure of ITO/PEDOT:PSS/Alq3:NPD/LiF/Al. The optical characteristics of the crystalline film is completely transparent at visible wavelengths and absorbs light at UV frequencies. Moreover, it exhibits emission quenching of photoluminescence intensity when more Alq3 added i.e. 2, 3 and 4 with respect to the host. In the electrical characterization, the optimized device (2:1 blend ratio) exhibits high sensitivity of 25,300 at −2 applied bias and under illumination of 40 mW/cm2 UV light. Response and recovery times of the UV sensor was found to be 0.69 s and 0.36 s, respectively. The result indicates that the blend of Alq3/NPD with its high photosensitivity and fast response to the UV light of 365 nm wavelength can be employed in the fabrication of a cost-effective and highly sensitive UV photodetector.

The demand for adequate image quality with low radiation doses for patients has greatly increased. This is especially true in the case of position verification in radiotherapy which requires a high number of images per patient. This study presents a physical characterisation of a new clinical detector named “Lassena (CsI)” based on a thick layer of structured thallium activated caesium iodide and complementary metal-oxide semiconductor technology with active pixel sensor architecture for general X-ray imaging and cone-beam computed tomography (CBCT) applications. We made a critical appraisal of its performance for the first time and determined its signal transfer property (STP) and its detective quantum efficiency (DQE) by acquiring the pre-sampling modulation transfer function (pMTF) and normalised noise power spectrum (NNPS) in addition to the dark current calculation. The investigation was conducted with the application of three X-ray beam qualities: (50 kV (RQA3), 70 kV (RQA5) and 90 kV (RQA7)) in compliance with the International Electrotechnical Commission (IEC 62220-1(2003)) standard. The STP was found to be linear with the coefficient of determination (R2) more than 0.9995 in all cases. The spatial resolution and NNPS results led to acceptable DQE values at all energies; in particular the DQE values at 0.5 line pairs per mm (DQE(0.5)) which were 0.46 for RQA3, 0.52-0.56 for RQA5 and 0.55-0.59 for RQA7. Lastly, the dark current was 2.51 pA/cm2 for a 50 μ m pixel pitch. For CBCT applications, Lassena (CsI) showed very promising results.