A facile molecularly engineered copper (II) phthalocyanine as hole transport material for planar perovskite solar cells with enhanced performance and stability

Perovskite solar cells (PSCs) demonstrate huge potential in photovoltaic conversion, yet their practical applications face one major obstacle: their instability. As to conventional hole transport materials (HTMs) such as spiro-OMeTAD, their future commercialization maybe hampered for the cost and instability. Here, we report a new HTM of copper (II) phthalocyanine with octamethyl-substituted function groups (CuMe2Pc). Unlike the normal edge on orientation of pristine copper (II) phthalocyanine (CuPc), we found that CuMe2Pc could form face-on molecular alignment when deposited on perovskite via vacuum thermal evaporation, resulting in higher hole mobility, more condense thin film structure and more hydrophobic surface. These properties are more favorable for hole transport and moisture resistance applications in PSCs. PSCs with planar structure were fabricated and tested, utilizing different phthalocyanines and spiro-OMeTAD as HTMs. PSCs with CuMe2Pc showed 25% higher power conversion efficiency (PCE) compared with those with CuPc. Furthermore, beneficial from the hydrophobic nature of CuMe2Pc, the devices with CuMe2Pc as HTM show improved stability and retained over 95% of their initial efficiencies even after storage in the humidity about 50% for 2000 h without encapsulation. This study demonstrates that CuMe2Pc is a potential HTM for fabricating low-cost and efficient PSCs with long-term stability.