K. Pradeesh

In situ intercalation strategies for device-quality hybrid inorganic-organic self-assembled quantum wells

Thin films of self-organized quantum wells of inorganic-organic hybrid perovskites of (C6H9C2H4NH3)2PbI4 are formed from a simple intercalation strategy to yield well-ordered uniform films over centimeter-size scales. These films compare favorably with traditional solution-chemistry-synthesized thin films. The hybrid films show strong room-temperature exciton-related absorption and photoluminescence, which shift with fabrication protocol. We demonstrate the potential of this method for electronic and photonic device applications.

Strong exciton-photon coupling in inorganic-organic multiple quantum wells embedded low-Q microcavity

Optoelectronic-compatible heterostructures are fabricated from layered inorganic-organic multiple quantum wells (IO-MQW) of Cyclohexenyl ethyl ammonium lead iodide, (C(6)H(9)C(2)H(4)NH(3))(2)PbI(4) (CHPI). These hybrids possess strongly-resonant optical features, are thermally stable and compatible with hybrid photonics assembly. Room-temperature strong-coupling is observed when these hybrids are straightforwardly embedded in metal-air (M-A) and metal-metal (M-M) low-Q microcavities, due to the large oscillator strength of these IO-MQWs. The strength of the Rabi splitting is 130 meV for M-A and 160 meV for M-M cavities. These values are significantly higher than for J-aggregates in all-metal microcavities of similar length. These experimental results are in good agreement with transfer matrix simulations based on resonant excitons. Incorporating exciton-switching hybrids allows active control of the strong-coupling parameters by temperature, suggesting new device applications.

Exciton switching and Peierls transitions in hybrid inorganic-organic self-assembled quantum wells

Hybrid organic-inorganic perovskite semiconductors provide significant opportunities as multifunctional materials for many electronic and optoelectronic applications. These include organic-inorganic light emitting diodes, organicinorganic field-effect transistors, and nonlinear optical switches based on strong exciton-photon coupling in microcavity photonic architectures. 1‐4 The basic structure of these lead II halide-based two-dimensional 2D pervoskites takes the general form R-NH32PbI4 where R is organic consisting of layers of corner-sharing lead iodide octahedra with bilayers of organic cations stacked between the inorganic layers. 5‐7 These form ‘natural’ multiple quantum well structures, where wells of the 2D inorganic semiconducting layer are clad by barriers of the wider bandgap organic layers. Typical layer thicknesses of well and barrier are 6 and 10 A, respectively. The low dimensionality of carriers confined within the inorganic layers by quantum confinement combined with the large dielectric mismatch giving dielectric confinement between the layers, enables formation of stable excitons with large binding energy even at room temperatures. 8,9 These hybrids are thermally stable up

Structural and optical studies of local disorder sensitivity in natural organic–inorganic self-assembled semiconductors

The structural and optical spectra of two related lead iodide (PbI) based self-assembled hybrid organic‐inorganic semiconductors are compared. During the synthesis, depending on the bridging of organic moiety intercalated between the PbI two-dimensional planes, different crystal structures are produced. These entirely different networks show different structural and optical features, including excitonic bandgaps. In particular, the modified organic environment of the excitons is sensitive to the local disorder both in single crystal and thin film forms. Such information is vital for incorporating these semiconductors into photonic device architectures. (Some figures in this article are in colour only in the electronic version)

Temperature-induced exciton switching in long alkyl chain based inorganic-organic hybrids

Photoluminescence and transmission is systematically explored in thin films of long–alkyl-chain-based inorganic-organic (IO) hybrids (CnH2n+1NH3)2PbI4 (n = 12, 16, 18) (CnPI) and NH3C12H22NH3PbI4 (DDPI). Such IO-hybrids, which form natural multiple quantum well structures stacked up along c-axis, possess strong room-temperature exciton transitions. These hybrids exhibit reversible phase transition of two different crystal phase transitions at easily accessible device temperatures. Flipping the structural phase is clearly reflected in switching of the excitons with corresponding photoluminescence and transmission changes showing clear thermal hysteresis. The phase-dependent switching of excitons is predominantly due to reversible crumpling of the inorganic PbI sheet networks. Systematic temperature dependent studies establish a correlation between the structure and optical exciton features. Such thermo-optic exciton switching suggests possible new photonic devices.

Naturally Self-Assembled Nanosystems and Their Templated Structures for Photonic Applications

Self-assembly has the advantage of fabricating structures of complex functionalities, from molecular levels to as big as macroscopic levels. Natural self-assembly involves self-aggregation of one or more materials (organic and/or inorganic) into desired structures while templated self-assembly involves interstitial space filling of diverse nature entities into self-assembled ordered/disordered templates (both from molecular to macro levels). These artificial and engineered new-generation materials offer many advantages over their individual counterparts. This paper reviews and explores the advantages of such naturally self-assembled hybrid molecular level systems and template-assisted macro-/microstructures targeting simple and low-cost device-oriented fabrication techniques, structural flexibility, and a wide range of photonic applications.

Strong exciton-photon coupling in layered perovskites embedded low-Q microcavity

Here we fabricated highly-layered perovskite Inorganic-Organic Hybrid Quantum Well (IO-HQW) structure and conveniently placed them into dielectric/metallic heterostructures. Upon angle tuning, the broad photonic mode of the microcavity is clearly split into two modes at the strong exciton resonance OI-HQW absorption. The large Rabi splitting (∼130meV) obtained is in good agreement with the theoretical models and paves way to new optoelectronic device applications.

Switcheable strong-coupling microcavities of inorganic-organic perovskite natural quantum wells

Room-temperature strong-coupling has been observed with large Rabi splitting of upto 202meV when layered inorganic-organic multiple quantum wells (IO-MQWs), are embedded in low-Q microcavities. Incorporating exciton-switching hybrid further allows active control of the strong-coupling parameters.