Solution-Processed Phototransistors Combining Organic Absorber and Charge Transporting Oxide for Visible to Infrared Light Detection

Abstract

This report demonstrates high-performance infrared phototransistors that use a broad-band absorbing organic bulk heterojunction (BHJ) layer responsive from the visible to the shortwave infrared, from 500 to 1400 nm. The device structure is based on a bilayer transistor channel that decouples charge photogeneration and transport, enabling independent optimization of each process. The organic BHJ layer is improved by incorporating camphor, a highly polarizable additive that increases carrier lifetime. An indium zinc oxide transport layer with high electron mobility is employed for rapid charge transport. As a result, the phototransistors achieve a dynamic range of 127 dB and reach a specific detectivity of 5 × 10 12 Jones under a low power illumination of 20 nW/cm 2 , outperforming commercial germanium photodiodes in the spectral range below 1300 nm. The photodetector metrics are measured with respect to the applied voltage, incident light power, and temporal bandwidth, demonstrating operation at a video-frame rate of 50 Hz. In particular, the frequency and light dependence of the phototransistor characteristics are analyzed to understand the change in photoconductive gain under different working conditions.

Noise and detectivity limits in organic shortwave infrared photodiodes with low disorder

“…Among flexible thin-film materials, organic semiconductors offer versatile tunability, mechanical flexibility, and broadband high performance 9,[11][12][13][14][15][16] . Therefore, organic bulk heterojunction (BHJ) photodiodes are used in our experimental studies.…”

Tuning the charge blocking layer to enhance photomultiplication in organic shortwave infrared photodetectors

“…Charges escape slowly from deep traps on account of high activation energies, leading to long lifetimes and high photoconductive gain and responsivity. 39,40 As displayed in Fig. 5c, the responsivity was inversely proportional to the illumination intensity, and the device with Bphen achieved 5.6 A W À1 (equivalent EQE = 660%) under a low light intensity of 0.2 mW cm À2 , resulting in a D* of 1.6 Â 10 9 Jones.…”

Organic Upconversion Imager with Dual Electronic and Optical Readouts for Shortwave Infrared Light Detection

“…The visible OLED is forward biased while the SWIR OPD is reverse biased. The OPD is a bulk heterojunction (BHJ) consisting of a SWIR-sensitive polymer [32][33][34][35] and a fullerene derivative [36] whose chemical structures can be found in Figure S1a, Supporting Information. Figure 1e presents the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) levels of each material.…”