Enhancing Intermolecular Interaction of Spiro-OMeTAD for Stable Perovskite Solar Cells with Efficiencies over 24%

The organic nature of 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD) has been noted as a stability-limiting factor in perovskite solar cells (PSCs). The requirement for a hygroscopic dopant (lithium bis(trifluoromethanesulfonyl)imide) and low doping efficiency further contribute to the role of spiro-OMeTAD in the easy degradation of PSCs. To resolve this issue, we report a simple strategy enabling the efficiency of spiro-OMeTAD-based PSCs to reach over 24% while greatly enhancing their operational stability. Three different tris(4-methoxyphenyl)amine coupled materials (TCMs) with different core units were synthesized and added in the spiro-OMeTAD hole-transporting layers (HTLs) resulting in enhanced intermolecular interactions. When each TCM was added to spiro-OMeTAD (5 mol % to spiro-OMeTAD), the highest PCE of over 24% was maintained over 90% during 1200 h of operation without encapsulation. This strategy enabled an intermolecular interaction route within the HTL that facilitates efficient hole transport and decreases the amount of dopant needed, which are key parameters for operational stability enhancement.