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

Two saddle‐shaped hole‐transporting materials (HTMs), α, β‐COTh‐Ph‐OMeTAD and β, β‐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 α, β‐COTh‐Ph‐OMeTAD demonstrates a high power conversion efficiency (PCE) of 17.59% with J sc = 21.32 mA cm −2 , V oc = 1.02 V, and FF = 80.75%, and the one based on β, β‐COTh‐Ph‐OMeTAD yields a higher PCE of 18.53% with J 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 α, β‐COTh‐Ph‐OMeTAD and β, β‐COTh‐Ph‐OMeTAD based on FCTC strategy are promising HTMs for highly efficient and stable PSCs.