Temperature-dependent luminescence spectra of Ruddlesden-Popper quasi-2D perovskites

The quasi-2D Ruddlesden-Popper (R-P) halide perovskite has been widely used in solar cells, light-emitting diodes, lasers and other optoelectronic devices due to its excellent photoelectric properties. However, the exciton-phonon interaction, which seriously affects the relaxation and transport characteristics of carriers, has not been fully revealed. Compared with the widely studied 3D perovskite structure, quasi 2D perovskite has a naturally formed quantum well structure with greater exciton binding energy and more obvious exciton effect. However, the exciton-phonon interaction of quasi 2D perovskite is still less studied. Therefore, a quasi-2D R-P perovskite film (PEA)2Csn-1PbnBr3n+1 has been prepared by solution method with a gain coefficient of ~1090.62 cm-1 and an amplified spontaneous emission of low threshold (~12.48 μJ/cm2). Based on this, we studied the luminescence properties of (PEA)2Csn-1PbnBr3n+1 film with temperature variation by using variable temperature fluorescence spectroscopy (77-300K) and transient absorption spectroscopy, in order to elaborate the influence of exciton-phonon interaction on its luminescence properties. It was found that in the low temperature domain (<120 K), The bandgap change caused by exciton-phonon interaction is relatively weak, and the lattice thermal expansion is dominant. With the increase of temperature, the exciton-phonon interaction has a great influence on the change of bandgap. On the other hand, the exciton-phonon interaction causes the line width of the luminescence spectrum to widen, but we observed the abnormal line width narrowing in the temperature range of 77 K-120 K, which is attributed to an energy transfer mechanism in the multi-quantum well caused by the localization effect, until after 120 K, the line widening caused by the exciton-phonon interaction is sufficient to reverse this trend. In this paper, the exciton-phonon interaction of quasi 2D perovskite is of guiding value for improving the optical properties and luminescence applications of quasi 2D perovskite.

准二维鲁德莱斯登-波珀卤化物钙钛矿（quasi-2D Ruddlesden-Popper (R-P) halide perovskite）凭借优异的光电性能，已被广泛应用于太阳能电池、发光二极管、激光器及其他光电器件中。然而，严重影响载流子弛豫与输运特性的激子-声子相互作用（exciton-phonon interaction）尚未被完全揭示。与被广泛研究的三维钙钛矿结构相比，准二维钙钛矿具有天然形成的量子阱结构（quantum well structure），其激子束缚能（exciton binding energy）更高，激子效应（exciton effect）也更为显著，但目前对准二维钙钛矿的激子-声子相互作用的研究仍相对较少。为此，本研究通过溶液法制备了(PEA)₂Csn₋₁PbnBr₃n₊₁型准二维R-P钙钛矿薄膜，其增益系数（gain coefficient）约为1090.62 cm⁻¹，放大自发辐射（amplified spontaneous emission）阈值低至约12.48 μJ/cm²。基于该样品，本研究采用变温荧光光谱法（variable temperature fluorescence spectroscopy，77~300 K）与瞬态吸收光谱法（transient absorption spectroscopy），研究了(PEA)₂Csn₋₁PbnBr₃n₊₁薄膜在温度变化下的发光特性，以阐明激子-声子相互作用对其发光特性的影响。研究发现，在低温区域（<120 K），激子-声子相互作用引发的带隙变化相对微弱，晶格热膨胀（lattice thermal expansion）占据主导地位；随着温度升高，激子-声子相互作用对带隙变化的影响显著增强。另一方面，激子-声子相互作用会导致发光光谱线宽展宽，但我们在77 K~120 K的温度范围内观察到了反常的线宽窄化现象，该现象可归因于局域效应（localization effect）引发的多量子阱（multi-quantum well）内能量转移机制（energy transfer mechanism）；直至120 K之后，激子-声子相互作用引发的线宽展宽效应才足以逆转这一趋势。本研究对准二维钙钛矿激子-声子相互作用的探讨，对改善准二维钙钛矿的光学性能及发光应用具有指导价值。