Phthalocyanine in perovskite solar cells: a review

Presently, due to the rapid development of perovskite solar cells (PSCs), their commercialization is not only attractive but perhaps the only choice to replace both thin film photovoltaics (PV) and conventional silicon PV. However, although the power conversion efficiency (PCE) of PSCs is has reached above 25%, which is suitable for their commercialization, their poor long-term stability with scalability remains a challenge due to the sensitivity of perovskites under ambient conditions. Therefore, the top and bottom layers sandwiching the perovskite layer are critical. In this case, the charge transport layers (CTLs) not only enable charge extraction but also play the role of encrusting, passivating, and supporting the perovskite layer. Therefore, the perovskite interface has a dominant influence on the performances of PSCs. In this case, phthalocyanines (Pcs) have a large pi-conjugated framework, outstanding thermal stability, excellent physical/chemical stability, low cost, and can be endowed with a tunable energy band, good carrier mobility, solubility in common solvents, and facile synthesis through their appropriate design, making them a robust charge selective layer, passivation layer or both in PSCs. In this review, we summarize the studies on the application of Pc compounds in PSCs, including dopant-free macrocycle molecules, from the perspectives of molecular engineering, doped hole transporting material (HTM), and employment of Pcs as additives in the perovskite layer or HTMs. This review provides helpful insight for further enhancing the efficiency of PSC devices, while improving their long-term operational life by utilizing Pc materials.