The mixing effect of organic cations on the structural, electronic and optical properties of FA_xMA_1−xPbI₃perovskites

Abstract

Organic-inorganic hybrid perovskites as new emerging functional materials stand out from numerous photovoltaic materials thanks to the unprecedentedly rapid improvement of their power conversion efficiency within a short period. To explore potentially more efficient photovoltaic candidates, the structural and electronic properties of FAMAPbI based on prototype MAPbI are investigated for superior performance. Specifically, structural relaxation is performed at the PBE+D2 level and the electronic and optical properties are investigated at the HSE + SOC level. Optical simulations show that significantly improved performance can be successfully achieved by means of the injection of FA cations. Moreover, the calculations of defect formation energies imply that MA-poor ambient conditions are energetically favorable to synthesize a variety of FA-doped pervoskite compounds FAMAPbI of different ratios. It is interesting to find that compared with the prototype MAPbI, the optical performance of the perovskite series FAMAPbI is effectively improved with an increase in FA content; meanwhile the relative stability of the perovskite series is also efficiently enhanced. Our study not only sheds new light on further understanding perovskite absorbers but also provides the basic rationale for designing new functional materials used for photovoltaics.

Formamidinium dopant effects on double perovskite Cs2AgBiBr6

“…This is in good agreement with the results of previous studies in which almost no organic cations are involved in the band edge states [39, 40]. Chen et al introduced FA dopants into perovskite MAPbI 3 , and found that organic cations generally did not contribute to the energy band edge [36].…”

“…The negative dopant formation energy indicates that the introducing FA impurities may be an exothermic process and can occur spontaneously, which is similar to that of Rb‐doped double perovskite Cs 2 AgBiBr 6 [28]. Chen et al found that, when the FA dopant concentration is 75% in FA x MA 1‐x PbI 3 , the dopant formation energy is the lowest among the mixing FA x MA 1‐x PbI 3 perovskites [36]. Volonakis et al have demonstrated the relationship between the dopant formation energy and the ionic radius of the A‐site cation, and found that doping organic cations such as MA and FA in the double perovskite A 2 InBiBr 6 can obtain relative stable structure [20].…”

Enhanced Stability and Optical Absorption in the Perovskite‐Based Compounds MA1−xCsxPbI3−yBry

“…Moreover, it is clearly shown that with the increase of Br content in Figure (a)–(d)or Figure (a)–(d), the main occupied states in the VBM are gradually changed from the σ‐antibonding states consisting of I‐5p and Pb‐6s to those of Br‐4p and Pb‐6s, whereas there is almost no obvious variation in the CBM dominated by Pb‐6p orbital. Additionally, there is still no significant impact of the doping of Cs on the electronic orbitals of band‐gap edges, although the band gap can be effectively tuned by means of A‐site ion doping within inorganic framework [BX 6 ] 4− , which is in good agreement with the previous studies . Specifically, it has been proposed that A‐site cations are mainly used to maintain the bulk in the charge neutrality .…”

Ethylammonium Lead Iodide Formation in MAPbI3 Precursor Solutions by DMF Decomposition and Organic Cation Exchange Reaction

“…Although various strategies have been proposed, such as doping at A, B, and X sites of the ABX 3 perovskite structure [11][12][13], grain boundary passivation [7,14,15], or replacing hydrophilic hole transport layer [16], none has resolved the stability issue successfully. Therefore, uncovering the scientific mechanism of the decomposition is imperative to address this issue.…”