Near‐Infrared Organic Phototransistors with p‐Channel Photosensitive Layers of Conjugated Polymer Composed of bis‐Octyldodecyl‐Diketopyrrolopyrrole and Benzothiadiazole Units

Abstract

A near‐infrared (NIR)‐absorbing conjugated polymer, poly[{2,5‐bis‐(2‐octyldodecyl)‐3,6‐bis‐(thien‐2‐yl)‐pyrrolo[3,4‐c]pyrrole‐1,4‐diyl}‐co‐{2,2′‐(2,1,3‐benzothiadiazole)‐5,5′‐diyl}] (PODTPPD‐BT), which is synthesized via a Stille coupling reaction, can play a dual role (charge transport and sensing) in NIR‐sensing organic phototransistors (OPTRs). The PODTPPD‐BT films, which feature two strong optical absorption peaks at wavelengths (λ) of 830 and 935 nm, possess a highly ordered crystalline state as evidenced by the synchrotron radiation grazing incidence X‐ray diffraction (GIXD) method. The OPTRs with the PODTPPD‐BT layers show typical p‐channel transistor behaviors in the dark, while their best dark performance is measured at a PODTPPD‐BT thickness (t) of 85 nm. The highest overall photocurrent is measured at t = 85 nm under illumination with three monochromatic NIR lights, while the highest photoresponsivity (RC) is obtained for the thickest PODTPPD‐BT layers (t = 145 nm). The flexible OPTRs with the PODTPPD‐BT layers demonstrate stable sensing characteristics upon optical on/off modulations using a high‐power NIR laser diode (λ = 905 nm) used for actual light detection and ranging (LiDAR) systems.

Near Infrared Light‐Sensing Organic Light‐Dependent Resistors Based on Dialkoxybenzothiadiazole‐Containing Conjugated Polymer

“…Here, it is worthy to note that the device current was relatively higher at the thicker PDPP-8OBT films, which can be attributed to the increased volume for charge transport as typically measured for sheet resistances of films. [26][27][28][29] Accordingly, as shown in Figure 2b (bottom panel), the electrical resistance (R H ) of devices was restricted to 4-6 TΩ even at 60 V, which complies with the low resistance requirement of LDRs. [30][31][32][33] In more detail, as displayed in Figure 2c (top panel), the specific electrical resistance (R HS,D ) of devices in the dark condition reached %20-40 EΩ cm À2 in the presence of slight deviations according to the film thickness and applied voltage.…”

Photogenerated Charge-Aided Low-Voltage Operation of n-Channel Organic Transistors with n-Type Conjugated Polymers─Toward Photosensor Applications

“…The photoresponsivity ( R C ), which is the ratio of net drain current under light ( I D,Light – I D,Dark ) to the incident light intensity ( P IN ), gradually decreased with the incident light intensity, irrespective of the wavelength. This trend reflects that the degree of charge recombination in the PIDTT-NDI layers became higher as the incident light intensity increased. − Finally, the continuous sensing characteristics were tested for the OFETs with the PIDTT-NDI PCLs ( t = 100 nm) upon optical on–off modulations of incident light. As shown in Figure , the drain current obviously changed according to the light-on and light-off states, irrespective of wavelengths.…”

Recent Advances in Organic Phototransistors: Nonvolatile Memory, Artificial Synapses, and Photodetectors

“…Park et al reported a near‐infrared organic phototransistor with a p‐channel based on poly(diketopyrrolopyrrole‐benzothiadiazole) (PDPPBT) with a narrow bandgap. [ 137 ] In thin films, close contact between DPP units can cause strong dipole interactions between carbonyl groups and nearby nitrogen atoms. Therefore, evenly distributed charge transfer complexes were formed in the crystalline domain of the channel layer to promote the photoresponse.…”