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Dye-sensitized solar cells (DSCs) have proven to be one of the best photovoltaic approaches for harnessing indoor/artificial light. Herein, we report two new molecularly engineered, cost-effective, metal-free, carbazole-based D–π–A sensitizers (YK 8 and YK 9) by judiciously varying their π-spacers, which are suitable for indoor photovoltaic applications. Using YK 8, we achieved an efficiency of 28.7% under standard 1000 lux Osram 14 W T2 cool day light fluorescent tube illumination with a power output of 68.88 μW cm−2 and 30.24% with a power output of 108.85 μW cm−2 under a higher illumination intensity of 1500 lux without co-sensitizers using iodide/triiodide electrolyte. With a small footprint/active area of 1.24 cm2, we could power a temperature sensor completely autonomously at a low light intensity of 500 lux, displaying the potential of these indoor photovoltaic devices to serve as energy sources for low-power sensors and actuators on the Internet of Things (IoT) network, reducing the dependence on batteries and leading to a smaller carbon footprint. The role of the π-spacer and its influence on recombination and device performance were explored via extensive interfacial studies.

We demonstrate that the polarity influence on the pyrene fluorescence band ratios (I3/I1) termed as the Ham effect can be effectively utilized to study the electrostatic interaction of CdTe nanoparticles (ζ = −46 mV) with the oppositely charged organic molecule, pyrenemethylamine hydrochloride (PMAH). As compared to water, the less polar nature of the QD's surface resulted in an increase in I3/I1 peak ratio of PMAH (from 0.34 to 0.54) when brought into close proximity. The lowering of the asymmetric stretching frequency of the carboxylate group of thioglycolic acid (1570 cm−1 to ∼1550 cm−1) and the drop in zeta potential of the nanoparticle from −46 mV to −8 mV indicate the interaction of PMAH with the nanoparticles. Control experiments with capping ligands, QDs with different surface charges (−46, −39, −35, −31, −20 and +21 mV) and negatively charged pyrene molecules invariably support the role of nanoparticles and their surface charge. The combined effects of charge neutralization and hydrophobicity increase lead to the organization of QDs into 2D sheet like superstructures, preserving their initial individuality.

Anisotropic nanocrystals of gold and silver are promising candidates for sensing and therapeutic applications because of their high extinction coefficient, increased NIR response and localization of hot spots at their tips. Herein, we report a viable room temperature synthetic strategy to prepare multi-branched gold nanocrystals of varying morphologies without the aid of additional nanoseeds or shape directing agents. By systematically modulating the bifunctional ligand to the Au3+ ion molar ratio ([L-DOPA]/[HAuCl4] = 0.15–1), the plasmon absorption was tuned from visible (530 nm) to NIR (930 nm). The corresponding microscopic studies showed a gradual transformation of the nanomaterial's morphology from multiply twinned spheres to branched stars and flowers. The detailed spectroscopic and microscopic studies have revealed that evolution of these branched nanocrystals proceeds through aggregation and subsequent overgrowth of initially produced spherical particles.