Revealing a new doping mechanism of spiro-OMeTAD with tBP participation through the introduction of radicals into HTM

Although lots of efforts have been devoted on new less hygroscopic dopants to address problems in hole transport materials (HTM), the long-time post-oxidation and the volatilization of 4-tert-butylpyridine (tBP) are still issues. A new doping mechanism for spiro-OMeTAD by disulfiram (TETD) is revealed in this work. Owing to its disulfide bond, TETD can be activated easily to produce reactive sulfur for the rapid oxidation of spiro-OMeTAD in the absence of oxygen with formation of [spiro-OMeTAD•]+[SC(S)N(C2H5)2]-. Thus, in this situation, the Li+ ion has the opportunity to coordinate tBP and fix each other in HTM film. DFT calculations suggest that the resulting favorable energy (with a ΔE of -1.29 eV) must come from the mutual interactions among Li+, TFSI−, and tBP, which is different from the well-known doping process that tBP would not participate in the doping reaction. As a result, the introduction of a new radical into the HTM greatly reduce device performance fluctuations due to the environmental dependence and inhibit tBP volatilizing for enhanced long-term stability. Rapid oxidation of spiro-OMeTAD in the absence of oxygen through additional addition of radicals into HTM. DFT calculations suggest that the resulting favorable energy must come from the mutual interactions among Li+, TFSI−, and tBP, which is different from the well-known doping process that tBP would not participate the doping reaction. [Display omitted]