A-Site Mixing to Adjust the Photovoltaic Performance of a Double-Cation Perovskite: It Is Not Always the Simple Way

Abstract

Considerable progress has been made in improving the performance of optoelectronic devices based on hybrid organic−inorganic perovskites of the form ABX 3 . However, the influences of A-site doping on the structure and dynamics of the inorganic perovskite crystal lattice and, in turn, on the optoelectronic performance of the resulting devices remain poorly understood at an atomic level. This work addresses this issue by combining the results of several experimental characterization methods for threedimensional MA 1−x DMA x PbBr 3 perovskite single crystals (MA, methylammonium; DMA, dimethylammonium). The results reveal a two-stage change in lattice with an increase in DMA content, which has completely opposite effects on the optoelectronic performance of the double-cation perovskite. At low DMA concentrations, fast reorientation of incorporated DMA cations strengthens the interaction between MA cations and the lattice without significant lattice distortion, which could suppress lattice fluctuation and thus improve the photovoltaic performance. At high DMA concentrations, the lattice get a severe distortion, leading to poorer photovoltaic performance.

High‐throughput compositional mapping of triple‐cation tin–lead perovskites for high‐efficiency solar cells

“…A‐site alloying hardly changes the energy levels of the valence band maximum (VBM) and conduction band minimum (CBM) because cations weakly interact with the octahedron matrix, thus contributing little to the orbit hybridization at the band edges. Even so, in Pb‐based perovskites, increasing the Cs content slightly raises the bandgap due to octahedral tilting, which influences the extent of the metal–halide orbital overlap 44 . In contrast, the undistorted cubic phase of Sn–Pb perovskites after Cs addition revealed that Cs causes only lattice contraction and no octahedral tilting, resulting in a minor electronic contribution at the band edges 45 .…”

“…Even so, in Pbbased perovskites, increasing the Cs content slightly raises the bandgap due to octahedral tilting, which influences the extent of the metal-halide orbital overlap. 44 In contrast, the undistorted cubic phase of Sn-Pb perovskites after Cs addition revealed that Cs causes only lattice contraction and no octahedral tilting, resulting in a minor electronic contribution at the band edges. 45 As a result, a small amount of Cs mixing (<12%) in A-sites has a negligible effect on the bandgaps of Sn-Pb mixed perovskites.…”

Crystal Growth and Photoelectric Properties of Dimethylammonium Doped CsPbBr3

“…With respect to A-site doping, previous studies have demonstrated the successful replacement of Cs, FA or MA in APbX 3 perovskite crystals with some proportion of relatively larger cations, such as ethylammonium, [22,23] guanidinium, [24,25] dimethylammonium (DMA), [26,27] and methylene-diammonium. [28] The larger cations doping has been shown to improve both the optoelectronic properties and the stability significantly.…”

“…[30] The MA 1−x DMA x PbBr 3 (0 ≤ x ≤ 0.7) series of perovskite single crystals were prepared by Yao et al The results showed that low concentration of DMA doping significantly improved the photovoltaic performance. [27] This enhancement is mainly attributed to the change of the inorganic lattice structure caused by A-site doping, such as lattice parameters, relaxation of lattice strain, octahedral tilt oscillations and local changes in the rotational dynamics of octahedra in the lattice. [28,31,32] Despite the progress made in the above-mentioned areas, little is known about the effect of DMA doping on the structural properties of CsPbBr 3 perovskite, which limits the further development of hybrid perovskite materials with a wide range of functions.…”