Dopant-Free and Green-Solvent-Processable Hole-Transporting Materials for Highly Efficient Inverted Planar Perovskite Solar Cells

Two saddle-shaped hole-transporting materials (HTMs), alpha, beta-COTh-Ph-OMeTAD and beta, beta-COTh-Ph-OMeTAD are designed with a strategy of flexible core with tunable conformation (FCTC) and applied in inverted planar perovskite solar cells (PSCs) as dopant-free HTMs. As a result, the device based on alpha, beta-COTh-Ph-OMeTAD demonstrates a high power conversion efficiency (PCE) of 17.59% withJ(sc) = 21.32 mA cm(-2),V-oc = 1.02 V, and FF = 80.75%, and the one based on beta, beta-COTh-Ph-OMeTAD yields a higher PCE of 18.53% withJ(sc) = 22.68 mA cm(-2),V-oc = 1.04 V, and FF = 78.48%. Moreover, the green-solvent-processed PSCs are also fabricated by dissolving the HTMs in ethyl acetate. Without any encapsulation, the devices based on both HTMs retain 80% of their initial PCEs after storage for 150 days in a glove box, and 60% of their initial PCEs after storing for 300 h in ambient air with 40% relative humidity. All these results demonstrate that the materials alpha, beta-COTh-Ph-OMeTAD and beta, beta-COTh-Ph-OMeTAD based on FCTC strategy are promising HTMs for highly efficient and stable PSCs.