Two-Step Solution-Processed Two-Component Bilayer Phthalocyaninato Copper-Based Heterojunctions with Interesting Ambipolar Organic Transiting and Ethanol-Sensing Properties

The two-component phthalocyaninato copper-based heterojunctions fabricated from n-type CuPc(COOC8H17)(8) and p-type CuPc(OC8H17)(8) by a facile two-step solution-processing quasi-Langmuir-Shafer method with both n/p- and p/n-bilayer structures are revealed to exhibit typical ambipolar air-stable organic thin-film transistor (OTFT) performance. The p/n-bilayer devices constructed by depositing CuPc(COOC8H17)(8) film on CuPc(OC8H17)(8) sub-layer show superior OTFT performance with hole and electron mobility of 0.11 and 0.02 cm(2) V-1 s(-1), respectively, over the ones with n/p-bilayer heterojunction structure with the hole and electron mobility of 0.03 and 0.016 cm(2) V-1 s(-1) due mainly to the more intense face-to-face - interaction in the CuPc(OC8H17)(8) sub-layer than that in CuPc(COOC8H17)(8) sub-layer, revealing the effect of different stacking sequence on tuning the OTFT performance of phthalocyanine-based bilayer heterojunctions. Furthermore, the chemiresistive devices fabricated from the p/n-bilayer heterojunction, with both Au and Indium tin oxide (ITO) interdigitated electrodes (IDEs), also display much better sensing properties to ethanol than those with n/p-bilayer heterojunction in terms of sensitivity and reversibility. Significantly, time-dependent current plot of the p/n-bilayer heterojunction with ITO IDEs reveals a detection limit as low as 100 ppm, nearly complete reversibility, and high selectivity to ethanol even at room temperature, rendering this novel two-component heterojunction device a great application potential in practical detecting ethanol.