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.