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

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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–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(COOC8H17)8 film on CuPc(OC8H17)8 sub‐layer show superior OTFT performance with hole and electron mobility of 0.11 and 0.02 cm2 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 cm2 V−1 s−1 due mainly to the more intense face‐to‐face π–π 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.