Recombination mechanisms in MA- and Cs&FA-based perovskites: composition versus photoluminescence analysis

Abstract Compositional tuning has been one of the approaches to increasing the stability of perovskites. The formation of defects in the crystalline lattice impacts not only stability but also the charge carrier recombination channels established in the film. In this work, the photoluminescence of MAPbI $$_{3-x}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow> <mml:mn>3</mml:mn> <mml:mo>-</mml:mo> <mml:mi>x</mml:mi> </mml:mrow> <mml:mrow/> </mml:mmultiscripts> </mml:math> Br $$_x$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mi>x</mml:mi> <mml:mrow/> </mml:mmultiscripts> </mml:math> and Cs $$_{0.17}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow> <mml:mn>0.17</mml:mn> </mml:mrow> <mml:mrow/> </mml:mmultiscripts> </mml:math> FA $$_{0.83}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow> <mml:mn>0.83</mml:mn> </mml:mrow> <mml:mrow/> </mml:mmultiscripts> </mml:math> PbI $$_{3-y}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow> <mml:mn>3</mml:mn> <mml:mo>-</mml:mo> <mml:mi>y</mml:mi> </mml:mrow> <mml:mrow/> </mml:mmultiscripts> </mml:math> Br $$_y$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mi>y</mml:mi> <mml:mrow/> </mml:mmultiscripts> </mml:math> thin films, measured at 70 K, was comparatively investigated to evaluate the influence of monovalent cations and halide anions on the formation of defects and resulting recombination mechanisms. To study the radiative transitions, measurements as a function of excitation power were done, and the spectral deconvolution performed followed by the estimation of $$\beta $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>β</mml:mi> </mml:math> and m parameter values. The $$\beta $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>β</mml:mi> </mml:math> parameter values clearly show a much higher density of defects on MA-based perovskites compared to Cs&amp;FA-based ones, while the m parameter values suggest an increase in this density with raise of the Br content. In the case of the broad and asymmetric emission spectra in MA-based perovskites, it was observed the coexistence of radiative recombination channels involving: (i) deep defects; (ii) charge carriers or excitons that are free or bound to shallow defects. For Cs&amp;FA-based perovskites, the luminescence is narrower and only includes the recombination of charge carriers or excitons bound to shallow defects. Additionally, it was found that in Cs&amp;FA-based perovskites, some radiative channels remain unchanged with varying I/Br ratio. Increasing the Br content, systematically widens the band gap. The results obtained impact the influence of composition on the discussion of perovskite stability and the variation in charge carrier recombination channels, demonstrating the relevance of photoluminescence in the discussion of both issues.\query{Please suggest whether the term ‘Cs&amp;FA-based’ can be changed to ‘Cs and FA-based’}