We demonstrate an extremely sensitive ammonia gas sensor based on vertical organic diode to exhibit a 1 ppb detection limit. Using phenyl-C61-butyric acid methyl ester (PCBM) as the sensing layer, the nano-porous structure enlarges the surface to volume ratio and hence realizes the ppb-regime sensitivity. The proposed vertical nano-junction (VNJ) organic diode is then investigated by changing the semiconducting materials (i.e. sensing material). In addition to a pure n-type or p-type sensing material, the blend of n/p organic semiconductor (PCBM/P3HT) is used to react with gas. Changing the n/p blending ratio from 0 to 100% delivers a tunable gas response to ammonia and nitric oxide, hence demonstrating a sensing map concept with good selectivity.
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