Charge Collection Characteristics Research Articles

Terpolymer Containing a meta-Octyloxy-phenyl-Modified Dithieno[3,2-f:2',3'-h]quinoxaline Unit Enabling Efficient Organic Solar Cells.

With the rapid development of small-molecule electron acceptors, polymer electron donors are becoming more important than ever in organic photovoltaics, and there is still room for the currently available high-performance polymer donors. To further develop polymer donors with finely tunable structures to achieve better photovoltaic performances, random ternary copolymerization is a useful technique. Herein, by incorporating a new electron-withdrawing segment 2,3-bis(3-octyloxyphenyl)dithieno[3,2-f:2',3'-h]quinoxaline derivative (C12T-TQ) to PM6, a series of terpolymers were synthesized. It is worth noting that the introduction of the C12T-TQ unit can deepen the highest occupied molecular orbital energy levels of the resultant polymers. In addition, the polymer Z6 with a 10% C12T-TQ ratio possesses the highest film absorption coefficient (9.86 × 104 cm-1) among the four polymers. When blended with Y6, it exhibited superior miscibility and mutual crystallinity enhancement between Z6 and Y6, suppressed recombination, better exciton separation and charge collection characteristics, and faster hole transfer in the D-A interface. Consequently, the device of Z6:Y6 successfully achieved enhanced photovoltaic parameters and yielded an efficiency of 17.01%, higher than the 16.18% of the PM6:Y6 device, demonstrating the effectiveness of the meta-octyloxy-phenyl-modified dithieno[3,2-f:2',3'-h]quinoxaline moiety to build promising terpolymer donors for high-performance organic solar cells.

Multi-layered blocking layers for dye sensitized solar cells

The introduction of novel hierarchical blocking layer (BL) between conductive fluorine-doped tin oxide (FTO) and nanocrystalline TiO2 plays a pivotal role for efficiency enhancement in dye-sensitized solar cells (DSSCs). Herein, we investigate the performance of DSSCs incorporating the TiO2 (T), TiO2/AZO (TA) and TiO2/AZO/TiO2 (TAT) BLs underneath the mesoporous TiO2 layer. The systematic characterizations demonstrate that the existence of the TAT layer not only serves as a BL but also functions as an auxiliary FTO layer. As a BL, the TAT layer reduces the charge recombination from FTO to electrolyte by improving the recombination resistance. Moreover, as an auxiliary FTO layer, the TAT layer enhances the interconnection between the mesoporous TiO2 layer and FTO by forming an ohmic contact. Due to the enhanced charge transfer and collection characteristics of the TAT layer, the overall energy conversion efficiency of the DSSC with the TAT layer was boosted by 40.0% in comparison to that of the DSSC with the T BL. The findings demonstrate that TAT is a promising alternative to the conventional TiO2 BL in highly efficient DSSCs.

Flexible Perovskite X‐Ray Detectors through Interfacial Modification with Perylene Diimide

AbstractFlexible direct X‐ray detectors based on perovskites have great potential for X‐ray imaging due to their high sensitivity, low detection limit, low‐cost, and large‐area fabrication. However, these detectors perform inefficiently at X‐ray‐to‐current conversion because of inadequate functional layer thickness and charge‐carrier recombination. Here, the fabrication of an integrated, self‐powered X‐ray detector based on CsPbBr3 quantum dots and a MAPbI3 photoelectric conversion layer embedded with perylene diimide molecules is reported. In addition to optimizing crystal domain formation and charge carrier extraction, the perylene diimide molecules also improve the electron mobility of MAPbI3 films by twofold. The integrated perovskite‐based X‐ray detector has a sensitivity of 143 169 ± 848 µC Gyair−1 cm−2 and a detection limit of 30.77 nGy s−1. The perylene diimide molecule at the grain boundary of MAPbI3 shows defect passivation and charge collection characteristics, leading to stable output over 30 bending cycles. This hybrid molecular approach provides insight into a general method to modify device performance using perylene diimide‐integrated detectors for X‐ray imaging of 3D objects with curved surfaces.

(Invited) Nanostructured Photoelectrochemical Electrodes and Electrocatalysts for Efficient Solar Energy Conversion

Photoelectrochemical (PEC) water splitting is a promising technique to directly convert solar energy into hydrogen energy for storage and transportation. PEC devices need to efficiently absorb sunlight and separate and collect the photocarriers. Herein we will present our recent work on the development of photonic structures for light trapping, PEC electrodes and electrocatalysts for water splitting. The importance of understanding both the light harvesting and the charge collection characteristics will be highlighted for the light trapping structural design. For electrocatalysts, we will focus on two-dimensional (2D) materials, and combine experimental and theoretical techniques to reveal the importance of the specific nanostructures for hydrogen evolution reaction and oxygen evolution reaction in electrolytes of different pH values. Our overall goal is to develop cost-efficient and robust photocatalysts and electrocatalyst to efficiently convert the abundant solar energy to clean, storable and transportable chemical fuels.

SOI Thin Microdosimeters for High LET Single-Event Upset Studies in Fe, O, Xe, and Cocktail Ion Beam Fields

The response of a 5- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> -thin silicon on insulator (SOI) 3-D microdosimeter was investigated for single-event upset applications by measuring the linear energy transfer (LET) of different high LET ions. The charge collection characteristics of the device were performed using the ion beam-induced charge collection (IBIC) technique with 3- and 5.5-MeV He <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> ions incident on the microdosimeter. The microdosimeter was irradiated with <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">16</sup> O, <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">56</sup> Fe, and <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">124</sup> Xe ions and was able to determine the LET within 5% for most configurations apart from <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">124</sup> Xe. It was observed that on average, measured LET was 12% lower for 30-MeV/u <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">124</sup> Xe ion traversing through different thickness Kapton absorbers in comparison to Geant4 simulations. This discrepancy can be partly attributed to uncertainties in the thickness of the energy degraders and the thickness of the SOI layer of the devices. The effects of overlayer thickness variation are not easily observed for ions with much lower LET as O and Fe. Based on that, it is difficult to make conclusion that the plasma effect is observed for 30-MeV/u <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">124</sup> Xe ions and further research to be carried out for ion with LET higher than 12 MeV/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> .

Tracking performance and simulation of capacitively coupled pixel detectors for the CLIC vertex detector

In order to achieve the challenging requirements on the CLIC vertex detector, a range of technology options have been considered in recent years. One prominent idea is the use of active sensors implemented in a commercial high-voltage CMOS process, capacitively coupled to hybrid pixel readout chips. Recent results have shown the approach to be feasible, though more detailed studies of the performance of such devices, including simulation, are required. The CLICdp collaboration has developed a number of ASICs as part of its vertex detector R&D programme, and here we present results on the performance of a CCPDv3 active sensor glued to a CLICpix readout chip. Charge collection characteristics and tracking performance have been measured over the full expected angular range of incident particles using 120 GeV/c secondary hadron beams from the CERN SPS. Single hit efficiencies have been observed above 99% in the full range of track incidence angles, down to shallow angles. The single hit resolution has also been observed to be stable over this range, with a resolution around 6 $\mu$m. The measured charge collection characterstics have been compared to simulations carried out using the Sentaurus TCAD finite-element simulation package combined with circuit simulations and parametrisations of the readout chip response. The simulations have also been successfully used to reproduce electric fields, depletion depths and the current-voltage characteristics of the device, and have been further used to make predictions about future device designs.

OVERMOS — CMOS Hi-Res MAPS detectors for HEP applications

The OVERMOS project investigates the use of Monolithic Active Pixel Sensors, fabricated using a standard low voltage, high resistivity substrate 180 nm CMOS technology, for tracking and vertexing in HEP applications. Following a description of the main features of this CMOS technology, details will be given of the design of the OVERMOS test pixel structures, which include active pixels, with in-pixel RO electronics, and basic pixel arrays. Preliminary experimental results of fabricated test structures, which include charge collection, obtained using in-pixel laser injection, and comparison of performances before and after neutron irradiation will be shown. Results of 3D TCAD simulation related to charge collection and DC characteristics of the pixel structures will be also shown.

Laser test studies on the single-sided dual-column 3D stripixelsilicon detector

The single-sided full-3D stripixel detector and the laser test system were introduced in this paper. The detector responses to different conditions (including detector bias voltage, laser illumination position, pulse generator parameters setting for driving laser device, etc) were measured and analyzed. Main detector parameters, including the depletion voltage, 2D position sensitivity response, charge collection characteristics with different bias voltages, noise distribution characteristics influenced by the different coupling modes of n+-strips and p+-strips electrodes to the readout chip channels, were obtained with 1060nm laser irradiation tests. The measurement results showed that the detector was position sensitive. Its depletion voltage was about 5V. The measured equivalent noise charge(ENC) of the detector system was about 730±10e.

3D silicon microdosimetry and RBE study using 12C ion of different energies

This paper presents a new version of the 3D mesa “bridge” microdosimeter comprised of an array of 4248 silicon cells fabricated on 10 µm thick silicon-on-insulator substrate. This microdosimeter has been designed to overcome limitations existing in previous generation silicon microdosimeters and it provides well-defined sensitive volumes and high spatial resolution. The charge collection characteristics of the new 3D mesa microdosimeter were investigated using the ANSTO heavy ion microprobe, utilizing 5.5 MeV He2+ ions. Measurement of microdosimetric quantities allowed for the determination of the Relative Biological Effectiveness of 290 MeV/u and 350 MeV/u 12C heavy ion therapy beams at the Heavy Ion Medical Accelerator in Chiba (HIMAC), Japan. The microdosimetric RBE obtained showed good agreement with the tissue-equivalent proportional counter. Utilizing the high spatial resolution of the SOI microdosimeter, the LET spectra for 70 MeV 12C+6 ions, like those present at the distal edge of 290 and 350 MeV/u beams, were obtained as the ions passed through thin layers of polyethylene film. This microdosimeter can provide useful information about the lineal energy transfer (LET) spectra downstream of the protective layers used for shielding of electronic devices for single event upset prediction.

3D Silicon Microdosimetry and RBE Study Using &lt;formula formulatype="inline"&gt;&lt;tex Notation="TeX"&gt;$^{12}{\rm C}$&lt;/tex&gt;&lt;/formula&gt; Ion of Different Energies

This paper presents a new version of the 3D mesa Bridge microdosimeter comprised of an array of 4248 silicon cells fabricated on 10 μm thick n-type silicon-on-insulator substrate. This microdosimeter has been designed to overcome limitations existing in previous generation silicon microdosimeters and it provides well-defined sensitive volumes and high spatial resolution. The charge collection characteristics of the new 3D mesa microdosimeter were investigated using the ANSTO heavy ion microprobe, utilizing 5.5 MeV He 2 + ions. Measurement of microdosimetric quantities allowed for the determination of the relative biological effectiveness of 290 MeV/u and 350 MeV/u 12 C heavy ion therapy beams at the Heavy Ion Medical Accelerator in Chiba (HIMAC), Japan. The microdosimetric RBE obtained showed good agreement with the tissue-equivalent proportional counter. Utilizing the high spatial resolution of the SOI microdosimeter, the LET spectra for 70 MeV 12 C +6 ions, like those present at the distal edge of 290 and 350 MeV/u beams, were obtained as the ions passed through thin layers of polyethylene film. This microdosimeter can provide useful information about the lineal energy transfer (LET) spectra downstream of the protective layers used for shielding of electronic devices for single event upset prediction.

Characterization of a Large Area Thinned Silicon Microdosimeter for Space and Particle Therapy

The tissue-equivalent proportional counter is the gold standard detector in microdosimetry. The energy deposited in its volume is equal to that of a single cell through the use of low pressure tissue-equivalent gas. To overcome its bulky gas-flow ensemble, high operating voltage and poor spatial resolution, a 20 μm-thick silicon microdosimeter with 9600 micron-sized sensitive volumes has been developed. Presented are the results from its initial characterization including electrical properties and charge collection characteristics obtained using induced charge collection techniques at ANSTO, Australia, and the ESRF, France. In addition, the results from a 290 MeV/u C-12 irradiation at HIMAC, NIRS, Japan, are presented.

3D cylindrical silicon microdosimeters: fabrication, simulation and charge collection study

This paper reports on the fabrication, simulation, and charge collection characteristics of a new generation of cylindrical silicon microdosimeters fabricated on SOI wafers. The devices consist of an array of p+ electrodes surrounded by trench n+ electrodes creating well defined, cylindrical sensitive volumes. A first batch of microsensors with 5.4 μm active thickness has been successfully fabricated. The devices are fully functional with good diode behavior and a depletion voltage of only 3 V. Their charge collection characteristics have been investigated using the IBIC technique with protons and alpha particles. The IBIC maps show a 100% yield of active cells in a microdosimeter array and full charge collection efficiency in the active area of the unit microsensors. These devices constitute an step forward in the current status of microdosimeters based on silicon technologies.

Nanostructured Electron-Selective Interlayer for Efficient Inverted Organic Solar Cells.

We report a unique nanostructured electron-selective interlayer comprising of In-doped ZnO (ZnO:In) and vertically aligned CdSe tetrapods (TPs) for inverted polymer:fullerene bulkheterojunction (BHJ) solar cells. With dimension-controlled CdSe TPs, the direct inorganic electron transport pathway is provided, resulting in the improvement of the short circuit current and fill factor of devices. We demonstrate that the enhancement is attributed to the roles of CdSe TPs that reduce the recombination losses between the active layer and buffer layer, improve the hole-blocking as well as electron-transporting properties, and simultaneously improve charge collection characteristics. As a result, the power conversion efficiency of PTB7:PC70BM based solar cell with nanostructured CdSe TPs increases to 7.55%. We expect this approach can be extended to a general platform for improving charge extraction in organic solar cells.

An Advanced Double SOI CMOS Pixel Detector Termination With Trench Interspace

In this paper, an advanced double SOI CMOS pixel detector termination with trench interspace is investigated. The proposed termination, where horizontal structure is replaced by the vertical structure, leads to an optimal distribution of electric fields and improves the breakdown voltage. Two-dimensional and three-dimensional physical level simulation results show that the termination presents superior breakdown and charge collection characteristics compared with the conventional termination structure even under irradiation. In addition, the impact of trench interspace dimension and oxide plug structure on the breakdown voltage of pixel detector have been studied.

3D-Mesa “Bridge” Silicon Microdosimeter: Charge Collection Study and Application to RBE Studies in $^{12}{\rm C}$ Radiation Therapy

Microdosimetry is an extremely useful technique, used for dosimetry in unknown mixed radiation fields typical of space and aviation, as well as in hadron therapy. A new silicon microdosimeter with 3D sensitive volumes has been proposed to overcome the shortcomings of the conventional Tissue Equivalent Proportional Counter. In this article, the charge collection characteristics of a new 3D mesa microdosimeter were investigated using the ANSTO heavy ion microprobe utilizing 5.5 MeV He <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> and 2 MeV H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> ions. Measurement of the microdosimetric characteristics allowed for the determination of the Relative Biological Effectiveness of the <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> C heavy ion therapy beam at the Heavy Ion Medical Accelerator in Chiba (HIMAC), Japan. Well-defined sensitive volumes of the 3D mesa microdosimeter have been observed and the microdosimetric RBE obtained showed good agreement with the TEPC. The new 3D mesa “bridge” microdosimeter is a step forward towards a microdosimeter with fully free-standing 3D sensitive volumes.

Charge Collection Characteristics of A Super-Thin Diamond Membrane Detector Measured With High-Energy Heavy Ions

A transmission particle detector based on a super-thin diamond membrane film which can also be used simultaneously as a vacuum window for ion beam extraction has been developed. Charge collection characteristics of a 6.8 μm-thick diamond membrane detector for high-energy heavy ions including 75 MeV Ne, 150 MeV Ar, 322 MeV Kr, and 454 MeV Xe have been investigated for the first time. Charge collection signals under single particle flux from the thin part are stable and are well distinguishable from background signals. This behavior suggests that the diamond membrane detector could be used for counting single ions. On the other hand, charge collection efficiency is found to decrease with increasing of charge generated in the diamond membrane detector. This suggests that the pulse height defect, which has been previously reported for Si and SiC detectors, also occurs in the diamond membrane detector.

Recent progress in organic photovoltaics: device architecture and optical design

Research on organic photovoltaic (OPV) materials and devices has flourished in recent years due to their potential for offering low-cost solar energy conversion. With a deepened understanding on the fundamental photovoltaic processes in organic electronic materials and the development of tailored materials and device architectures, we have seen a rapid increase in the efficiency of OPV devices to over 10%, which attracts tremendous commercial interests for further development and manufacturing. Here, we review recent progress in the field of organic photovoltaics, particularly on various innovative device architectures and optical designs to maximize the power conversion efficiency of OPV cells for a given set of photoactive donor and acceptor materials. Following an introduction of the basic device operation of organic photovoltaic cells and the advances in active materials, we firstly present different device architectures that have been used to optimize the charge generation and collection characteristics within the OPV devices. We then discuss various methods to manage and manipulate the light wave propagation in OPV devices for more complete absorption of the incident light, an important area that has been underexplored so far.

Large Area Silicon Microdosimeter for Dosimetry in High LET Space Radiation Fields: Charge Collection Study

Silicon microdosimeters for the characterisation of mixed radiation fields relevant to the space radiation environment have been under continual development at the Centre for Medical Radiation Physics for over a decade. These devices are useful for the prediction of single event upsets in microelectronics and for radiation protection of spacecraft crew. The latest development in silicon microdosimetry is a family of large-area n-SOI microdosimeters for real-time dosimetry in space radiation environments. The response of n-SOI microdosimeters to 2 MeV H and 5.5 MeV He ions has been studied to investigate their charge collection characteristics. The studies have confirmed 100% yield of functioning cells, but have also revealed a charge sharing effect due to diffusion of charge from events occurring outside the sensitive volume and an enhanced energy response due to the collection of charge created beneath the insulating layer. The use of a veto electrode aims to reduce collection of diffused charge. The effectiveness of the veto electrode has been studied via a coincidence analysis using IBIC. It has been shown that suppression of the shared events allows results in a better defined sensitive volume corresponding to the region under the core electrode where the electric field is strongest.

Impact of Well Structure on Single-Event Well Potential Modulation in Bulk CMOS

Perturbations in N-well potential have been shown to strongly affect the charge collection, charge sharing, and parasitic bipolar transistor characteristics. In this paper, temporal and spatial characteristics of the well-potential modulation are characterized through 3-D TCAD simulations. Effects of well-contact layout, ion energy, and technology process parameters for a 90-nm bulk CMOS process are investigated.

Charge Collection Studies and Electrical Measurements of Heavily Irradiated 3D Double-Sided Sensors and Comparison to Planar Strip Detectors

Three-dimensional (3D) silicon detectors offer advantages over standard planar devices as more radiation hard sensors. These detectors and their applications in the upgrades of the LHC experiments are discussed. 3D detectors with a double-sided geometry have been fabricated as very short strip detectors with similar inter-column spacing as proposed for the ATLAS pixel detector and LHCb vertex locator upgrades. The detectors have been irradiated up to a fluence of 2 × 1016 cm-2 1 MeV equivalent neutrons, which is twice the expected dose of the inner pixel layer of the ATLAS detector and of the upgraded LHCb vertex locator for LHC high luminosity upgrade (HL-LHC) operation. Electrical measurements show a lateral depletion voltage of only 4 V for the device before irradiation which increases to 200 V after an irradiation to a fluence of 1 × 1016 cm-2 1 MeV equivalent neutrons. The strip isolation of the p-type detectors was robust to the maximum fluence. Charge collection studies have been performed with analogue readout with 25 ns shaping time, as required for LHC experiments. The response of the detectors to high energy electrons from a 90Sr source and a collimated pulsed laser light source are shown and compared with planar devices. The 3D detector, operated at no more than 350 V, is shown to have superior charge collection characteristics to planar devices for all the fluence range expected at HL-LHC even when compared to planar devices operating at 1000 V. When operated at a bias voltage of 350 V the 3D detector collects 2.8 times more charge than a p-type planar device operated at 1000 V after a fluence of 1016 cm-2 1 MeV equivalent neutrons. Charge multiplication in 3D detectors is also reported, in both 90Sr and laser tests, which leads to further enhancement in the charge collection and signal-to-noise ratio of the detector. The effect is demonstrated, through laser tests, to occur close to the junction electrode.