Expanding the absorption and photoresponse of 1D lead–halide perovskites via ultrafast charge transfer

Abstract

Low-dimensional metal halide perovskites are attracting extensive attentions due to their enhanced quantum confinement and stability compared to three-dimensional perovskites. However, low dimensional connectivity in the inorganic frameworks leads to strongly bounded excitons with limited absorption properties, which impedes their application in photovoltaic devices. Here, we show that by incorporating a strong electron accepting methylviologen (MV) cation, charge transfer (CT) at the organic/inorganic interface can effectively tune the optical properties in one-dimensional (1D) lead-halide perovskites. Both 1D MVPb2I6 and MVPb2Br6 display expanded absorption and photoresponse activity compared to CT inactive cations. The photoinduced CT process in MVPb2I6 was further characterized by transient absorption spectroscopy, which shows an ultrafast CT process within 1 ps, generating charge separated states. Our work unveils the interesting photophysics of these unconventional 1D perovskites with functional organic chromophores.

Nanocrystal‐Enabled Perovskite Heterojunctions in Photovoltaic Applications and Beyond

“…[70] Analogous charge transfer excitons have also been observed in several 1D hybrid organic/inorganic metal halide semiconductors and are attributed to hybrid states at the interface between the small molecule and metal halide framework. [73,74] We emphasize that the above discussion assumes a relatively abrupt heterojunction between two semiconductors. Creating and retaining such an abrupt perovskite/perovskite heterojunction is challenging due to the MHPs' low formation enthalpy, their solubility, and high ionic mobility.…”

“…[ 70 ] Analogous charge transfer excitons have also been observed in several 1D hybrid organic/inorganic metal halide semiconductors and are attributed to hybrid states at the interface between the small molecule and metal halide framework. [ 73,74 ]…”

Absorption Edge Fine Structure in the PyPbI3 Perovskite Revealed by Variable-Temperature UV–Vis Diffuse Reflectance Spectroscopy

“…As a result of their unique electronic, structural, and optical properties, one-dimensional (1D) organic–inorganic halide perovskites are being examined extensively as attractive materials from both a fundamental and application viewpoint. Crystals of these materials exhibit structures in which the inorganic chains of face-sharing lead iodide octahedra (wires) are surrounded by organic spacer molecules. − Two types of optical transitions are characteristic of 1D organic–inorganic iodides: (i) strong room-temperature excitonic (intrachain) transitions and (ii) charge-transfer transitions between the inorganic chains and the organic molecules. The latter transitions appear in a lower energy region relative to the intrachain excitonic regions.…”

“…The absorption/DR spectra of various 1D organic lead iodides displayed such resonance band maxima at 3.33−3.29 eV (372−377 nm), 4 3.14−3.03 eV (395−409 nm), 5 and ∼3.33 eV (372 nm). 6 The spectral manifestation and absorption intensity associated with charge-transfer transitions appear to depend first of all on the nature of the organic species. For instance, a methylviologen lead iodide single crystal and ethylviologen lead iodide thin film display a structureless tail reaching ∼2.0 eV (620 nm) in optical absorption spectra; 1−3 note that viologens are bipyridinium derivatives.…”

“…In comparison, the excitonic resonance was observed as an opposite resonance (low-energy minimum adjacent to a high-energy maximum; see Figure S3 for a further explanation) in the absorption spectra obtained from diffuse reflectance (DR) spectra subsequent to a Kubelka–Munk transformation. The absorption/DR spectra of various 1D organic lead iodides displayed such resonance band maxima at 3.33–3.29 eV (372–377 nm), 3.14–3.03 eV (395–409 nm), and ∼3.33 eV (372 nm) …”