Solution-Processed Tunable Spectral Response Photodetectors Enabled by Acidochromic Polymers

Journal article, 2026

Solution-processed tunable broadband photodetectors are fabricated by using acidochromic polymers in photodiode and phototransistor geometries with SnO2/polymer p-n heterojunctions. This organic-inorganic heterojunction works as a rectifying junction and bilayer channel of the photodiodes and phototransistors, respectively. In both devices, the lower bandgap acidochromic polymers (PIDT-BAB, PIDT-BIB, and PIDT-BVB) work as the photoactive layer, whereas n-type SnO2 works as the electron transport layer, and the devices show high spectrally selective blue and green sensitivity. The responsivity, detectivity, and response time of these photodiodes are in the range of 20–40 mA/W, 4–7.5 × 10⁹ Jones, and ∼7–10 s, respectively. The phototransistors are fabricated by using high-κ Li-Al2O3 gate dielectric, which enables them to reach their operating voltage within 2 V. Furthermore, the thin-film transistors (TFTs) show a large variation of threshold voltage with light intensity, with good linearity of variation with illumination power. The responsivity, detectivity, and response time of these phototransistors are in the same range as those of the photodiodes. Additionally, the spectral response of the photodiodes is tuned from the visible to the NIR region by using vapor-phase trifluoroacetic acid (TFA) due to their acidochromic effect in a reversible way, indicating their possible application as an optoelectrical switch.