High‐Responsivity and Fast‐Response Organic Phototransistor Based on Dinaphtho[2,3‐b:2′,3′‐f]Thieno[3,2‐b]Thiophene

Organic phototransistors (OPTs) are promising as low‐cost detectors compatible with plastic‐substrate electronics for visible light communication (VLC) systems. However, enhancing their sensitivity without sacrificing speed remains challenging. In this work, we report on an OPT based on dinaphtho[2,3‐b:2′,3′‐f]thieno[3,2‐b]thiophene (DNTT) optimized for detecting blue light. The device employs an Al/Al 2 O 3 /DNTT/Au layered structure fabricated at ≤100°C on a PEN substrate by shadow‐mask patterning. Key performance metrics include stable low‐voltage transistor operation, a field‐effect mobility in the range 0.16–0.24 cm 2 V −1 s −1 , and a low contact resistance (≈12 kΩ·cm). Under low‐intensity illumination (≈10 − 8 W cm −2 ) the phototransistor achieves an exceptional responsivity of ≈ 250 A/W and a specific detectivity on the order of 10 1 2 Jones, indicating competitive weak‐light sensing capability. Even at higher light levels (≈10 − 3 W cm −2 ), it maintains a large photosensitivity up to ≈120. High‐frequency tests demonstrate fast and detectable response up to 150 kHz. The device thus offers a rare combination of high sensitivity and fast response. These results represent a substantial advancement for organic optoelectronics, suggesting that the proposed OPT design is a promising candidate for future high‐speed VLC and other applications requiring lightweight, high‐performance photodetectors in the visible range.