Solution Processed Highly Efficient H2S Gas Sensor With Sub-ppb Detection Limit Based on Self-Aligned Thin Film of PCPDTBT Decorated With CdS Nanoparticles

In the present work, a facile method to develop poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4- $\text{b}^{\prime} $ ] dithiophene)-alt-4,7(2,1,3 benzothiadiazole)] (PCPDTBT)/CdS composite thin film with the integration of photoirradiation of the nanocomposite (NC) solution, simple and inexpensive floating film transfer method (FTM), and solvent vapor annealing (SVA) has been demonstrated. The film is applied to organic field-effect transistor (OFET) in top contact bottom gate (TCBG) configuration to evaluate the gas sensing performance for various concentrations of reducing and toxic H ₂ S gas at room temperature. The synergetic effect of the photoirradiation and the presence of CdS, FTM, and SVA enhance the molecular ordering of the polymer matrix. Photoirradiated PCPDTBT/CdS NC film exhibits a maximum charge carrier mobility of $\sim 3.4\times 10^{-{3}}$ cm ² / $\text{V}\cdot \text{s}$ , which is many folds higher than the pristine PCPDTBT film. Favorable $\pi $ – $\pi $ and electrostatic interactions after photoirradiation and self-aligned nature of FTM film enhance the interfacial interactions between CdS and PCPDTBT. Additionally, the state-of-the-art technique "SVA" offers enhanced crystallinity and excellent charge transport along the polymer chain, which significantly improves sensitivity. Photoirradiated-SVA-annealed PCPDTBT/CdS composite film-based OFET sensors consistently show enhanced sensitivity compared to the pristine PCPDTBT and PCPDTBT/CdS composite. Particularly, the photoirradiated-SVA-annealed PCPDTBT/CdS composite sensor achieves significantly enhanced response of $\sim $ 81% to 1-ppm exposure of H ₂ S gas, compared to the pristine PCPDTBT ( $\sim $ 71%) and PCPDTBT/CdS ( $\sim $ 76%) NCs. Additionally, excellent response-recovery behavior (e.g., $\sim $ 5 and $\sim $ 90 s, respectively), good ambient stability, and excellent selectivity are observed.