Ruddlesden–Popper (RP) phase metal halide organo perovskites are being extensively studied due to their quasi-two dimensional (2D) nature which makes them an excellent material for several optoelectronic device applications such as solar cells, photo-detectors, light emitting diodes (LEDs), lasers etc. While most of reports show use of linear carbon chain based organic moiety, such as n-Butylamine, as organic spacer in RP perovskite crystal structure, here we report a new series of quasi 2D perovskites with a ring type cyclic carbon group as organic spacer forming RP perovskite of type (CH)2(MA)n−1PbnI3n+1; CH = 2-(1-Cyclohexenyl)ethylamine; MA = Methylamine). This work highlights the synthesis, structural, thermal, optical and optoelectronic characterizations for the new RP perovskite series n = 1–4. The demonstrated RP perovskite of type for n = 1–4 have shown formation of highly crystalline thin films with alternate stacking of organic and inorganic layers, where the order of PbI6 octahedron layering are controlled by n-value, and shown uniform direct bandgap tunable from 2.51 eV (n = 1) to 1.92 eV (n = 4). The PL lifetime measurements supported the fact that lifetime of charge carriers increase with n-value of RP perovskites [154 ps (n = 1) to 336 ps (n = 4)]. Thermogravimetric analysis (TGA) showed highly stable nature of reported RP perovskites with linear increase in phase transition temperatures from 257 °C (n = 1) to 270 °C (n = 4). Scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX) are used to investigate the surface morphology and elemental compositions of thin films. In addition, the photodetectors fabricated for the series using (CH)2(MA)n−1PbnI3n+1 RP perovskite as active absorbing layer and without any charge transport layers, shown sharp photocurrent response from 17 nA/cm2 for n = 1 to 70 nA/cm2 for n = 4, under zero bias and low power illumination conditions (470 nm LED, 1.5 mW/cm2). Furthermore, for lowest bandgap RP perovskite n = 4, (CH)2MA3Pb4I13 the photodetector showed maximum photocurrent density of ~ 508 nA/cm2 at 3 V under similar illumination condition, thus giving fairly large responsivity (46.65 mA/W). Our investigations show that 2-(1-Cyclohexenyl)ethylamine based RP perovskites can be potential solution processed semiconducting materials for optoelectronic applications such as photo-detectors, solar cells, LEDs, photobatteries etc.
Hybrid metal halide perovskites, typically known for their photovoltaic applications, have recently gained traction as a potential energy-storage material because of their promising gravimetric capacities as lithium-ion battery electrode materials....
Organometal halide perovskites are being extensively studied as they can serve as an excellent active medium in various optoelectronic devices such as solar cells, light-emitting diodes (LEDs), lasers, etc. We report the fabrication of highly controlled single-phase mixed halide two-dimensional (2D) perovskites by successive doping of inorganic dopant, potassium iodide (KI), in 2D perovskite 2-(1cyclohexenyl) ethylammonium lead bromide, (C 6 H 9 C 2 H 4 NH 3 ) 2 PbBr 4 (CHPB). Our computational investigations further confirm the thermodynamic stability of mixed anion lattices. A stoichiometric increase of KI in CHPB beyond critical passivation levels results in a uniform bandgap tunability of thin films from the UV (∼3.21 eV) to green (∼2.50 eV) region of spectra. Distinctly linear, tunable, and single-phase strong room-temperature exciton absorbance (∼401−508 nm) and emission peaks (∼416−518 nm) in the blue-green spectral region are observed with the increase of KI concentration levels in thin-film samples. Doped two-dimensional (2D) perovskite films exhibit a minimum stokes shift parameter of 40 meV, which is very small compared to the conventional route of mixing two perovskite precursor solutions. X-ray diffraction studies show that the layered structure of doped 2D perovskite thin films remains intact despite high KI concentration levels. Charge transport studies of doped 2D perovskite thin films demonstrate a decline in the lifetime of photogenerated charge carriers with an increase of iodide concentration. Combining several experimental and computational techniques, we find that increased carrier effective masses and consequent formation of strongly bound excitons cause the decrease in carrier lifetime. In short, our present study reveals a promising low-cost solution-processable approach to fabricate single-phase mixed halide 2D perovskites to achieve unprecedented exciton tunability in low-dimensional optoelectronic materials.
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