Quasi‐Planar Core based Spiro‐Type Hole‐Transporting Material for Dopant‐Free Perovskite Solar Cells

Abstract Hole‐transporting material (HTMs) are crucial for obtaining the stability and high efficiency of perovskite solar cells (PSCs). However, the current state‐of‐the‐art n‐i‐p PSCs relied on the use of 2,2′,7,7′‐tetrakis(N,N‐di‐ p ‐methoxyphenylamine)‐9,9′‐spirobifluorene (spiro‐OMeTAD) exhibit inferior intrinsic and ambient stability due to the p ‐dopant and hydrophilic Li‐TFSI additive. In this study, a new spiro‐type HTM with a critical quasi‐planar core ( Z‐W‐03 ) is developed to improve both the thermal and ambient stability of PSCs. The results suggest that the planar carbazole structure effectively passivates the trap states compared to the triphenylamine with a propeller‐like conformation in spiro‐OMeTAD. This passivation effect leads to the shallower trap states when the quasi‐planar HTMs interact with the Pb‐dimer. Consequently, the device using Z‐W‐03 achieves a higher V oc of 1.178 V compared to the spiro‐OMeTAD's 1.155 V, resulting in an enhanced efficiency of 24.02 %. In addition, the double‐column π – π stacking of Z‐W‐03 results in high hole mobility (~10 −4 cm 2 V −1 s −1 ) even without p ‐dopant. Moreover, when the surface interface is modified, the undoped Z‐W‐03 device can achieve an efficiency of nearly 23 %. Compared to the PSCs using spiro‐OMeTAD, those with Z‐W‐03 exhibit enhanced stability under N 2 and ambient conditions. This superior performance is attributed to the quasi‐planar core structure and the presence of multiple CH/π and π – π intermolecular stacking in Z‐W‐03 . The multiple CH/π and π–π intermolecular contacts of HTMs can improve the hole hopping transport. Therefore, it is imperative to focus on further molecular structure design and optimization of spiro‐type HTMs incorporating quasi‐planar cores and carbazole moieties for the commercialization of PSCs.