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(COOC 8 H 17 ) 8 and p ‐type CuPc(OC 8 H 17 ) 8 by a facile two‐step solution‐processing quasi‐Langmuir–Shäfer 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(COOC 8 H 17 ) 8 film on CuPc(OC 8 H 17 ) 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 π–π interaction in the CuPc(OC 8 H 17 ) 8 sub‐layer than that in CuPc(COOC 8 H 17 ) 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.