Temperature-Dependent Band Gap in Two-Dimensional Perovskites: Thermal Expansion Interaction and Electron–Phonon Interaction

Abstract

Two-dimensional organic–inorganic perovskites have attracted considerable interest recently. Here, we present a systematic study of the temperature-dependent photoluminescence on phase pure (n-BA)2(MA) n−1Pb n I3n+1 (n = 1–5) and (iso-BA)2(MA) n−1Pb n I3n+1 (n = 1–3) microplates obtained by mechanical exfoliation. The photoluminescence peak position gradually changes from a red-shift for n = 1 to a blue-shift for n = 5 with an increase in temperature in the (n-BA)2(MA) n−1Pb n I3n+1 (n = 1–5) series, while only a monotonous blue-shift has been observed for the (iso-BA)2(MA) n−1Pb n I3n+1 (n = 1–3) series, which can be attributed to the competition between the thermal expansion interaction and electron–phonon interaction. In the (n-BA)2(MA) n−1Pb n I3n+1 (n = 1–5) series, the thermal expansion interaction and electron–phonon interaction are both gradually enhanced and the former progressively dominates the latter from n = 1 to n = 5, resulting in the band gap versus temperature changing from a red-shift to a blue-shift. In contrast, both of these factors show a weaker layer thickness dependence, leading to the monotonous blue-shift in the (iso-BA)2(MA) n−1Pb n I3n+1 (n = 1–3) series.

Filterless Polarization‐Sensitive 2D Perovskite Narrowband Photodetectors

“…Only one emission peak can be observed in room‐temperature photoluminescence (PL) spectrum locating around 522 nm (Figure f), which can be ascribed to the free exciton emission according to previous reports . No defect‐related emission peak is observed from low‐temperature PL spectra, suggesting the excellent quality of our as‐synthesized crystals (Figure S1, Supporting Information) . The room‐temperature reflection spectrum exhibits two peaks locating around 514 and 559 nm, respectively.…”

Local Energy Landscape Drives Long-Range Exciton Diffusion in Two-Dimensional Halide Perovskite Semiconductors

“…The position of the main PL resonance, which we refer to herein as the high-energy (HE) peak, does not shift significantly from ∼1.9 eV upon decreasing temperature from 300 to 80 K. This lack of shift is consistent with the strong influence of phonons on the exciton properties 11 , 32 , 33 that counterbalances the usual PL red shift in 3D perovskites attributed to the thermal contraction of the crystal within this temperature range 34 , 35 rather than other effects such as self-trapped excitons. 32 The red-shift behavior is recovered over the range of 120 to 10 K where the contribution of optical phonons should be negligible. Indeed, the lowest optical phonon mode energy in similar systems has been reported to be ∼10 meV, 35 − 37 corresponding to threshold temperatures of around ∼120 K. Further evidence for the influence of phonons on the exciton properties is seen in the decrease in the PL resonance width of the HE peak from ∼99 meV at 300 K to 22 meV at 100 K ( Figure S19 ).…”

Dual‐Stimuli‐Responsive Photoluminescence of Enantiomeric Two‐Dimensional Lead Halide Perovskites

“…With increasing temperature, the former leads to widened bandgaps due to the expansion of crystal structure while the latter results in an opposite effect because of the enhanced coupling between electrons and lattice vibration. [17,45,46] The evolution of bandgap (E g ) can be expressed by Equation ( 2) using the one oscillator model and assuming a linear TE:…”

“…[21][22][23] On the other hand, a few newest studies have also disclosed that 2D HOIPs can be significantly sensitive to thermal stimulus because of cooperative thermal expansion (TE) and electron-phonon (EP) interactions. [17,24] As expected 2D hybrid organic-inorganic perovskites (HOIPs) are highly responsive to external stimuli and therefore have application potential as sensing materials. Though their optical properties upon singular thermal or pressure stimulation have been recently investigated, their dual-stimuli-responsive behaviors have not yet been explored.…”

“…[15] The incorporation of both organic and inorganic components in these 2D HOIPs give rise to additional structural and quantum degrees of freedom which could enable them to respond to external stimulus in a remarkably different way compared with traditional semiconducting materials. [16,17] In this regard, these 2D HOIPs could serve as "smart" materials to sensitize environmental changes such as pressure, temperature, light, electric, and magnetic forces, [18][19][20] therefore, have application potentials in corresponding optoelectronic devices. Considering the high quality emission of these 2D HOIPs, it is natural to explore their optical properties in response to external stimuli and understand the underlying mechanism.…”