Zinc Phthalocyanine Conjugated Dimers as Efficient Dopant‐Free Hole Transporting Materials in Perovskite Solar Cells

Abstract

Four ZnPc‐dimers with 2,5‐thienyl (ZnPc−th−ZnPc 1 ), 2,7‐fluorenyl (ZnPc−flu−ZnPc 2 ), 3,6‐bisthienylldiketopyrrolopyrrole (ZnPc−DPP−ZnPc 3 ) and 1,4‐phenyl (ZnPc−p−ZnPc 4 ) bridges have been studied as dopant‐free hole transporting materials (HTMs) in perovskite solar cells (PSCs). The synthesis and characterization of ZnPc−th−ZnPc 1 and ZnPc−flu−ZnPc 2 dimers are reported for the first time. Steady state and time resolved photoluminescence demonstrate the good hole‐extraction capability of these materials. The best efficiencies obtained for dimers 1 , 2 , 3 and 4 are 15.5 %, 15.6 %, 16.8 % and 15.7 %, respectively, without the addition of dopants. Besides, these derivatives demonstrated better stability both in dark storage conditions with a relative humidity <20 % for 500 h and at 50 °C with a relative humidity >60 % for 160 h when compared to doped spiro−OMeTAD. The push‐pull nature of dimer ZnPc−DPP−ZnPc 3 has led to the highest efficiency among the ZnPc derivatives under study demonstrating that donor‐acceptor‐donor systems can be good alternatives to commonly used materials due their energy levels, low cost and the final morphology of the hole transporting layer.