Enhancement in operational current of PTB7 based ammonia gas sensor utilizing F4-TCNQ as P-type dopant

We demonstrate a (poly[(4,8-bis(2-ethylhexyloxy)-benzo-(1,2-b:4,5-b)dithiophene)− 2,6-diyl-alt-(4-(2-ethylhexyl)− 3-fluorothieno[3,4-b]thiophene-)− 2-carboxylate-2,6-diyl)]) (PTB7) based ammonia gas sensor with high operational current up to 10−4 A. Using (2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) (F4-TCNQ) as a p-type dopant for PTB7, the operation current under driving voltage of 5 V was effectively increased to 1.5×10−4 A, while that of a standard device was only 3×10−6 A. According to the study of space-charge-limited current and ultraviolet photoemission spectroscopy (UPS), the enhanced operational current can be attributed both to the higher mobility and lower carrier injection barrier of the F4-TCNQ doped PTB7. Detailed comparative analysis between the F4-TCNQ doped sensor and the non-doped sensor was also studied. The increased operational current and the current drop during sensing of the F4-TCNQ doped sensors are both beneficial to the realization of low-cost circuitry sensing system, which demonstrates the potential of the strategy of utilizing p-type doping in organic gas sensors for the developing of affordable point-to-care (POC) devices.