Anomalous Current Decrease Under Illumination in Ambipolar Phototransistors Based on PTCDI‐C₅ Crystals Embedded in C₈‐BTBT Thin Film

Abstract

Most organic thin film‐based phototransistors exhibit an increase in current under illumination owing to the trapped photogenerated minority charge carriers, which enhance the accumulation of majority carriers in the semiconductor layer of the device. Recent research reveals that, on employing a unique active layer structure, phototransistor devices exhibit abnormal photoresponse behaviors under certain conditions: hole‐dominated current decreases under illumination and shows an anomalous dependence on irradiance. The current decreases with increasing irradiance. When the irradiance is increased further, a moderate current increase is observed. Under a constant negative bias, when a discrete light pulse is turned on, the current decreases sharply and then slowly increases to saturation in the beginning and it starts to increase when illumination is ceased. These anomalies are analyzed, and the changes in current are modeled using a mathematical model based on the simultaneous trapping and release of both photogenerated holes and electrons.

Negative Phototransistors with Ultrahigh Sensitivity and Weak‐Light Detection Based on 1D/2D Molecular Crystal p–n Heterojunctions and their Application in Light Encoders

“…[17] The implementation strategies of NPTs can be categorized into the charge-transfer effect, the photothermoelectric effect, the bolometric effect, etc. [18][19][20][21][22][23][24][25] Among them, charge transfer typically occurs at the interface of multilayer p-n heterojunctions that are commonly used to fabricate NPTs, which is achieved by the recombination of charge carriers in conductive channels with opposite charges from other semiconductor layers upon illumination. [19,20,26] Despite progresses have been achieved, the development of NPTs is clearly still in its infancy as compared to well-developed PPTs, and faces urgent challenges that need to be addressed, e.g., photosensitivity (P) and detectivity (D*) as important performance parameters are still very poor for NPTs.…”

Wavelength and Polarization Sensitive Synaptic Phototransistor Based on Organic n-type Semiconductor/Supramolecular J-Aggregate Heterostructure

“…Most interestingly, at higher V G ≈ 50 V, I DS increased up to a blue illumination intensity of 320 μW cm –2 and then finally decreased, while I DS instantly decreased under red illumination (NPC; negative photocurrent) as shown in Figure b, c. Although the absolute photosensitivity varies from device to device, all devices show both PPC and NPC characteristics (Figure S7 and Table S2). The bidirectional photoresponse is a prerequisite for retinomorphic applications for motion detection and recognition (Figure S1c) and has so far been rarely reported in organic phototransistors. , …”

“…The bidirectional photoresponse is a prerequisite for retinomorphic applications for motion detection and recognition (Figure S1c) 45 and has so far been rarely reported in organic phototransistors. 26,46 The operating mechanism of PPC can be explained via an energy diagram and a floating gate transistor architecture of the Cl 2 -NDI/core−shell PBI-1 heterostructure (Figure 2d, f). Cyclic voltammetry results show that Cl 2 -NDI and PBI-1 form a type-II heterostructure; the lowest unoccupied molecular orbital (LUMO)/highest occupied molecular orbital (HOMO) energies are at −4.29 eV/−7.20 eV and −3.90 eV/−5.93 eV for Cl 2 -NDI and PBI-1, respectively (Figure S8).…”

Polymer-Gated Transistors with Only One Solution-Processed, Single Crystalline Organic Microwire for Light and Oxygen Detection

“…Among the solution processable OSCs, N , N ′-dipentyl-3,4,9,10-perylenedicarboximide (PTCDI-C 5 ) is a perylene tetracarboxylic-diimide (PTCDI) derivative that has been widely studied as an n -type OSC owing to its molecular design with a conjugated polyaromatic perylene backbone, which has high electron affinity and strong π–π stacking interaction. − It is also a potential material for the solution process because the additional side chains introduced to the perylene backbone increase the solubility for typical organic solvents. However, previously reported results of solution-processed PTCDI-C 5 crystals on Si/SiO 2 substrate indicated low charge carrier mobility (μ FET ∼ 6.9 × 10 –5 cm 2 /V·s) under ambient conditions (with rapid deterioration after a few hours without a passivation layer) or vacuum or N 2 conditions, , similar to the transistors with a thermally deposited thin film layer. , Recently, OFETs with a combination of PTCDI-C 5 crystals and other OSC materials were reported to form via solution pinning and were successfully fabricated and characterized as ambipolar transistors or phototransistors under ambient conditions. − However, the electronic characteristics of PTCDI-C 5 crystal-based devices have not been thoroughly studied.…”