Abstract
The suitable band structure is vital for perovskite solar cells, which greatly affect the high photoelectric conversion efficiency. Cation substitution is an effective approach to tune the electric structure, carrier concentration, and optical absorption of hybrid lead iodine perovskites. In this work, the electronic structures and optical properties of cation (Bi, Sn, and TI) doped tetragonal formamidinium lead iodine CH(NH2)2PbI3 (FAPbI3) are studied by first-principles calculations. For comparison, the cation-doped tetragonal methylammonium lead iodine CH3NH3PbI3 (MAPbI3) are also considered. The calculated formation energies reveal that the Sn atom is easier to dope in the tetragonal MAPbI3/FAPbI3 structure due to the small formation energy of about 0.3 eV. Besides, the band gap of Sn-doped MAPbI3/FAPbI3 is 1.30/1.40 eV, which is considerably smaller than the un-doped tetragonal MAPbI3/FAPbI3. More importantly, compare with the un-doped tetragonal MAPbI3/FAPbI3, the Sn-doped MAPbI3 and FAPbI3 have the larger optical absorption coefficient and theoretical maximum efficiency, especially for Sn-doped FAPbI3. The lower formation energy, suitable band gap and outstanding optical absorption of the Sn-doped FAPbI3 make it promising candidates for high-efficient perovskite cells.
Highlights
Over the last several years, hybrid organic-inorganic perovskite solar cells have become one of the most attractive photovoltaic technologies, with easy solution fabrication and high conversion efficiencies[1,2,3,4,5,6,7,8]
Compared with un-doped methylammonium lead iodine CH3NH3PbI3 (MAPbI3) perovskite, Sn-doped MAPbI3 perovskite have a small band gap, which can further enhance the photovoltaic performance of perovskite solar cells in the near-infrared spectrum[30, 31]
Considered the ion radius and the number of outside electrons, three types of atoms (Bi, Sn, and TI) were chosen as the typical cation-doped in the MAPbI3 and formamidinium lead iodine CH(NH2)2PbI3 (FAPbI3)
Summary
Before the optimization of the cation-doped perovskite structure, the lattice constants of tetragonal MAPbI3 and FAPbI3 supercells are fully relaxed. For the TI-doped MAPbI3/FAPbI3 structure, the Fermi level is lower than the valence band maximum, as shown in the Fig. 2(c) and (f). Compared with the PDOS of Pb atom, more sattes of TI in the TI-doped MAPbI3/FAPbI3 distributed in the high energy region, which further confirms that the TI is an acceptor defect in the doped MAPbI3/FAPbI3 systems. The optical absorption spectrum of TI-doped MAPbI3/FAPbI3 is lower than that of un-doped structures in most of the visible light region. The relatively small formation energy of Sn-doped MAPbI3/ FAPbI3 indicates that it is easy to dope Sn in the tetragonal MAPbI3/FAPbI3 structure. The lower formation energy, suitable band gap and outstanding optical absorption of the Sn-doped FAPbI3, enable it has great potential applications for the high-efficient perovskite cells
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