Ruddlesden-Popper 2D perovskites of type (CHCHNH)(CHNH)PbI (n = 1-4) for optoelectronic applications.

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)(MA)PbI; 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 PbI 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)(MA)PbI RP perovskite as active absorbing layer and without any charge transport layers, shown sharp photocurrent response from 17 nA/cm for n = 1 to 70 nA/cm for n = 4, under zero bias and low power illumination conditions (470 nm LED, 1.5 mW/cm). Furthermore, for lowest bandgap RP perovskite n = 4, (CH)MAPbI the photodetector showed maximum photocurrent density of ~ 508 nA/cm 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.