Effects of the Dopant Site on the Absorption Properties of CsPb_1–xM_xI₂Br (M = Ge, Sn, Sr, and Cu): A First-Principles Investigation

Abstract

In order to find low-toxic light-absorbing materials for perovskite solar cells, the electronic structures and optical absorption spectra of doped perovskites CsPb 1−x M x I 2 Br (M = Ge, Sn, Sr, and Cu) have been investigated with the first-principles method. Ge-and Sn-doped perovskites display monotonously decreased band gaps with increasing x, opposite to Sr-and Cu-doped ones. Different from group IV Ge and Sn elements, Sr and Cu dopants show distinct electronic characteristics, that is, weak interaction with halogens because of the d orbitals splitting in octahedral complexes and unique density of states and band-decomposed charge densities. Meanwhile, Ge, Sn, and Cu dopants prefer substituting Pb sites in the CsI-terminated surfaces based on thermodynamic consideration, and the dopants accumulating on surfaces will deteriorate the optical absorption of perovskites based on the comparison of the absorption spectra of various doped structures. Therefore, this study provides a theoretical insight into the declined absorption spectra with the increasing concentration of dopants in experimental observations.

97.3% Pb-Reduced CsPb1–xGexBr3 Perovskite with Enhanced Phase Stability and Photovoltaic Performance through Surface Cu Doping

“…Thus the blue-shift photoluminescence spectrum for CsPb 1– x Cu x Br 3 quantum dot has been observed in experiment . In addition, the interaction between electron-poor Cu atoms and Br atoms can split the d orbitals of Cu that occupy the Fermi level, so that a large amount of impurity states are found in the band gap of CsPb 1– x Cu x Br 3 (see Figure S3) and easily become nonradiative recombination centers.…”

“…The alkali earth cation doping significantly reduced the Pb component but enlarged the band gap and exciton binding energy in the resultant perovskite and deteriorated the efficiency due to the strong effect of s orbitals. , Trivalent cation substitution − was also an approach to reduce the toxicity and improve the PSC performance, but these dopants greatly distorted the band structures and induced trap states to deteriorate photovoltaic properties. Although the transition-metal cation dopants improved the stability and trap states of CsPbBr 3 , the eliminated toxic Pb was <5%. − It is thought that it is a challenge for single-cation doping to dramatically reduce the toxic Pb component.…”

“…Note that two cations simultaneously substituting the toxic Pb could completely eliminate the toxic Pb and enhance the thermal stability, such as in the double-perovskite Cs 2 AgInCl 6 . , Motivated by this, employing a two-cation doping method might be a promising way. In general, the d orbitals of the Cu dopant could enhance the optical absorption, and the Ge dopant could reduce the band gap accompanied by reduced exciton binding energy, which is important for the optoelectronic performance. , Hence, employing Ge and Cu cations simultaneously to substitute the Pb component (viz codoping) might be favorable to realize the environment-friendly high-performance perovskites. It should be noted that nevertheless, the charge states of Ge and Cu cations are different from those of cations in double perovskites, so that the roles, such as the doping position, stability, and so on, of these cations are disparate.…”

Unveiling the roles of halogen ions in the surface passivation of CsPbI3 perovskite solar cells

“…Because lead is a heavy metal, there is a strong relativistic effect between lead and halogen atoms. 29 Thus, the spin orbit coupling (SOC) effect was considered in all DFT calculations in this work.…”

The properties, photovoltaic performance and stability of visible to near-IR all inorganic perovskites

“…[1][2][3] In order for the perovskite to function efficiently as a light harvester in the solar cell, it must be stable under environmental conditions (especially moisture) [4][5][6] and have high photostability for long term use. [7][8][9] The general formula of basic halide perovskites is ABX 3 where A is generally an organic cation (methylammonium -MA + , formamidinium -FA + ) but can be also an inorganic cation (Cs + ); B is a divalent metal cation (Pb 2+ , Sn 2+ ,Ge 2+ , Sr 2+ , and Cu 2+ ) [10][11][12][13] and X is a halide anion (Cl À , Br À , I À ).…”