Quasi three-dimensional lead iodide perovskite using pyridine-2,5-diamine and 4,4′-bipyridine with tunable electronic structure, carrier transport, optical absorption properties

The introduction of functional diamino organic cations between inorganic Pb–I octahedrons to form a new quasi three-dimensional (3D) diamino perovskite is a strategy for expanding the family of perovskite materials, obtain excellent photovoltaic materials, and solve the problems of low thermal and chemical stability of traditional perovskites. In this work, the electronic structure, carrier transport and optical absorption properties of two new perovskites with pyridine-2,5-diamine (PDA) and 4,4′-bipyridine (BPD) as the organic cations are investigated using first-principles calculations. It is found that diamino pyridine and bipyridine have a strong effect on the perovskite band structure. The results show that, unlike for the traditional perovskite where the organic cations do not contribute to the conduction band minimum (CBM) and valence band maximum (VBM), the C–C ppπ∗ anti-bonding orbital and the 2p orbital of N in the pyridine ring of PDA and BDP contribute to the CBMs of the two perovskites. Interestingly, the NH of two pyridine rings in 4,4′-bipyridine (BPD) is similar to diamine, and the bound state provided by the C–C ppσ∗ orbital appears in the band gap of (BPD)PbI4, strongly affecting its optical properties. The results show that diamino pyridine and bipyridine effectively adjust the band structure of the organic-inorganic perovskite, and also affect the carrier transport and optical absorption characteristics. In particular, bipyridine perovskite displays better and more balanced electron and hole transport characteristics and greater optical absorption, which is helpful for the design and fabrication of more efficient and stable organic-inorganic perovskite photovoltaic devices.