Swadesh Kumar Gupta

Small weight percentages, 0.05≤ wt% ≤0.4, of reduced graphene oxide (rGO) nanoflakes are dispersed in the 2‐(4’‐octylphenyl)‐6‐dodecyloxynaphthalene (8‐PNP‐O12) liquid crystalline semiconducting material, and current–voltage (I–V) characteristics along with the charge transport mechanism in the smectic B (SmB) and smectic A (SmA) phases are investigated. It is a well‐known fact that the mobility of charge carriers significantly depends on the molecular ordering of a mesophase; therefore, the correlation of charge transport with molecular geometry has been scrutinized by carrying out the polarized optical microscopy and small/wide‐angle X‐ray scattering and I–V measurements. Due to the improved π–π interactions between rGO nanoflakes and 8‐PNP‐O12, the composite matrix liberates a massive amount of charge carriers, leading to a tremendous increase in the conduction current from nA to μA. The 8‐PNP‐O12/rGO matrix is suitable for nonlinear organic electronics due to its superior charge transport properties.

Cesium-lead halide perovskite nanoparticles are a promising class of luminescent materials for color and efficient displays. However, material stability is the key issue to solve before we can use these materials in modern displays. Encapsulation is one of the most efficient methods that can markedly improve the stability of perovskite nanoparticles against moisture, heat, oxygen, and light. Thus, we urgently need a low-cost, reliable, and device-compatible encapsulation method for the integration of nanomaterials into display devices. Here, we propose a facile encapsulation method to stabilize perovskite nanoparticles in thin polymer porous films. Using porous polymer films, we achieved good photoluminescence stability in the harsh environment of high temperature, high humidity and strong UV illumination. The good UV stability benefitted from the unique optical properties of the porous film. Besides, we observed photoluminescence enhancement of CsPbBr₃ nanoparticle films in a high humidity environment. The stable CsPbBr₃ nanoparticle thin porous film provides high brightness (236 nits) and great color enhancement for LCDs and is characterized by simple fabrication with easy scalability, thus it is very suitable for modern LCDs.

Quantum dot light emitting diodes (QLEDs) emerges as a potential display technology due to its ultra‐saturated colors, small turn on voltage (V _on ) and high efficiency (ŋ). However, the internal quantum efficiency (IQE) of QLED devices nearly reach its ideal level, and leave light outcoupling as the only possible way to improve the external quantum efficiency (EQE). This might need a different shape of the core shell, device structure and re‐optimization of the device. In this paper, we synthesized CdSe with CdS/ZnS based red, blue and green quantum rods (QRs) and fabricated electroluminescent QRs light emitting diodes (QRLEDs), this is the first study to report for the blue QRLEDs. The solution processed zinc oxide (ZnO) nano‐particles (NP) are used as an electron transport layer. The maximum luminance and EQE values of the devices are 1288, 420 and 13 cd/m ² and 5.7% and 0.18% and 0.093 %, for the red, green and blue LEDs, respectively. This kind of new QRLEDs shows a great potential for the use of next generation high color gamut display.

A new hybrid post‐synthetic and in‐film encapsulation method of colloidal perovskite nanoparticles is disclosed. The stabilization of the encapsulated perovskites against oxygen and humidity is tested and discussed. The convenience and scalability of this method opens avenue for perovskites to display application.

Semiconductor quantum rods (QRs) show a polarized emission, which opens up the possibility of the enhancement of both brightness and color for liquid crystal displays (LCD) in the form of quantum rod enhancement films (QREFs) for LCD backlights. However, the QR alignment over a large area, suitable for displays, is a challenge. Inkjet printing of QREFs, introduced here, allows fabrication of well-aligned, uniform QREFs on photoaligned substrates using optimized QR inks. We observed that the ink composition and printing conditions affect the QR alignment quality significantly. A relative humidity of 50% with an exposure energy of 1 J cm⁻² for the photoalignment process provided optimal conditions for QREFs. We have successfully shown a good QR alignment for 2.5-inch films and were able to align QRs in multiple layers. Thus, fabricated QREFs show a polarization ratio of 7.2 : 1 for the emitted light. These QREFs were combined with a blue LED and deployed as a backlight unit for an LCD which shows a brightness of ∼250 nits with an optical efficiency of ∼8%, reaching an NTSC of 109% in a CIE1976 color space. Thus, these printed QREFs, over a large area, provide an unprecedented increase of 77% in the optical efficiency of the LCDs and simultaneously offer better color performance.

The effect of Ultra Violet (UV) irradiation on the high temperature chiral nematic (N^*) mesophase has been investigated. The controlled UV exposure produced bending in rod shape molecules. The bending of molecules affects their long molecular axis; therefore, the relaxation mode associated with the rotation of molecules along the long molecular axis shifts toward the higher frequency. The UV irradiation also increases the cholesteric plane spacing of N^*LC molecules. The a.c. conductivity of N^*LC has been increased enormously after UV irradiation. The efficiency of opto-dielectric effect has also been evaluated with the variation of bias voltage in the present investigation.