Two-dimensional phthalocyanine-based molecular additives realize efficient hole transport and enhanced ion immobilization for durable perovskite solar cells

Perovskite solar cells (PSCs) have demonstrated high promises in low-cost manufacture and outstanding power conversion efficiencies (PCEs), however, long-term operational stability has become the major obstacle challenging the scalable application of this technology. Although the state-of-the-art hole transport layer (HTL) based on Spiro-OMeTAD becomes the indispensable component in high-efficiency PSCs, the dopants in the HTLs cause severe stability issues of ion migration and phase segregation, all of which induce the degradation of HTLs in the aspects of film conductivity and microstructures. Here we rationally design a two-dimensional phthalocyanine-based molecular additive (TB-C8-Ni) for the HTLs in order to enhance the carrier transportation and immobilize the ions. The incorporation of [8-(4-tert-butylphenoxy)octyl]oxy alkyl units as the side groups in TB-C8-Ni is essential to increase the solubility and improve the HTL uniformity. The superior planar structure of TB-C8-Ni favors the hole transportation and suppresses the migration of lithium ion under the environmental stress, which achieves reliable HTLs and devices. Consequently, the devices based on TB-C8-Ni exhibit boosted open-circuit voltage and fill factor, delivering an increased efficiency from 20.93% to 22.34%. More importantly, the additive TB-C8-Ni in the HTLs reinforces the moisture stability of devices, enabling to maintain 90% of initial efficiency after 2300 h in air.