Modeling the imaging performance of prototype organic x‐ray imagers

Abstract

A unified Monte Carlo and cascaded systems model for the simulation of active-matrix flat-panel imagers is presented. With few input parameters, the model simulated the imaging performance of previously measured flat-panel imagers with reasonable accuracy. The model is used to predict the properties of conceptual flat-panel imagers based on organic semiconductors on plastic substrates. The model suggests that significant improvements in resolution and detective quantum efficiency could be achieved by operating such a detector in a back-side illuminated configuration, or by employing two imaging arrays arranged face-to-face. The effect of semiconductor properties on the conceptual imagers is investigated. According to the model, a photodiode quantum efficiency of 25% and dark current of less than 100 pA mm(-2) would be satisfactory for a prototype imager, while a competitive imager would require a photodiode quantum efficiency of 40-50% with a dark current of less than 10 pA mm(-2) to be quantum limited over the radiographic exposure range.

Fully Inkjet‐Printed Organic Photodetectors with High Quantum Yield

“…[ 23,24 ] Here we make use of DOD inkjet printing, [ 25 ] that allows the defi nition of structures with a lateral resolution down to 10 μ m (depending on the nozzle size, the substrate surface energy and the ink surface tension), to develop organic-based photodetectors with a completely additive approach, where both the electrodes and the photoactive layer are printed. [ 2 ] Aiming at largearea applications in the fi eld of visible light or X-ray digital imagers, we focus on devices with an active area of about 100 × 100 μ m. [26][27][28] Thanks to a thorough optimization of the deposition of the various layers, we obtain excellent optoelectronic performances for the fully printed devices, with good yield and reproducibility.…”

Experimental validation of Monte Carlo (MANTIS) simulated x‐ray response of columnar CsI scintillator screens

“…12,21 In the model produced by Blakesley and Speller, 12 zero incidence angle simulation results were compared against experimental data from two systems with different columnar CsI screens. The validation was performed by overplotting the experimental MTF with simulated results, no quantitative FOM was used.…”

“…11 The main difference between the code MANTIS and the work cited above is the fact that MANTIS uses a list-mode approach for accounting of energy depositions and optical photon generation in the scintillator and can accommodate a structure with a large number of columns in the scintillator device. A recent study by Blakesley and Speller 12 implemented a Monte Carlo-based model of the full x-ray detection process in flat panel arrays ͑both indirect and direct detection types͒ from generation of the x-ray photons to charge readout and electronic noise in the photodiode layer. However, their model was meant to provide broad comparisons between theoretical detectors and not to give detailed descriptions of detector image quality.…”

Flexible image sensor array with bulk heterojunction organic photodiode

“…Bulk heterojunction blends 12 of electron donors and acceptors have exhibited highly efficient exciton dissociation in photovoltaic devices. 15 Alternative photosensor approaches, such as using lateral coplanar electrodes 8,16 or phototransistors, 17 show acceptable dark current but significantly reduce the fill factor of a pixel in a photosensing array and hence the sensitivity of each pixel. 1͑a͔͒ is typically kept below a few hundred nanometers 13,14 to increase the built-in electric field.…”

“…3͑a͒. 15, an imager array only needs EQE of 40%-50% with dark currents of less than 0.1 nA cm −2 to be quantum limited over x-ray exposure range. resolution.…”