Synthesis, Defect Structure and Photo-physics of Ternary Pnictide Nanocrystals

Non-Technical Summary

Photonic and optoelectronic applications consume nearly 30% of all energy produced. The two environmentally friendly photonic technologies expected to have the largest impact are solid-state light sources (light emitting diodes (LEDs)) for energy efficient lighting, and photovoltaics (PVs) for generating solar electricity. Materials currently dominating the photonics market are not sustainable and run into issues with stability, use of toxic materials such as cadmium, tellurium or lead, or rare and expensive elements such as indium or gallium.

An economically viable solution relies on discovery of scalable and low-cost earth-abundant materials with low toxicity (RoHS compliant) and requiring minimal energy input for both development and integration into applications. With this project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research at NSF, Prof.

Ayaskanta Sahu and New York University and his research group will investigate methods to produce ternary pnictides nanocrystals comprising of earth-abundant, low-cost, non-toxic elements (e.g. zinc tin phosphide) amenable to large-scale, sustainable production. This integrated research and education program aims to drive fundamental advances in the discovery and development of this new generation of unexplored photonic nanostructures, accelerating technological innovations involving these materials and expanding the frontiers of nanoscience.

The primary goal is to provide detailed insight into various solution-growth mechanisms and synthetic procedures for complex material systems, thus advancing the field of nanocrystal synthesis and providing a pathway for rational design and incorporation of multicomponent nano-crystalline systems in functional photonic devices. This project involving materials science, engineering, chemistry and physics, offers a diverse platform to engage, train and educate the next generation of engineers and scientists starting from K-12 students to undergraduates and graduate students, and instill a culture of active collaboration.

The project also provides a complementary education and outreach NEXUS program that strives to increase research participation and promote an interdisciplinary environment for women, black and Latino students, and other underrepresented minorities (URMs), and involves developing an instruction-oriented active hands-on learning kit by URM students for demonstration in K-12 Summer Science Camps and workshops at New York City schools and partner institutions in the United States.

Technical Summary

This project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research at NSF, aims to synthesize sustainable ternary II-IV-V2 (II = Zn, Mg, Sr; IV = Si, Sn, Ge; V = N, P) colloidal quantum dots (CQDs), understand the complex phase behavior, defect structure and effect of cation disorder on the photo-physics of individual CQDs and assemblies of these CQDs, and control the optoelectronic properties of II-IV-V2 films to such an extent that fabrication of light-emitting and light harvesting photonic devices that will achieve high efficiencies is enabled. Compared to the III-Vs, which are the workhorses of photonic applications, II-IV-V2 CQDs, with tunable band gaps owing to quantum confinement, are estimated to exhibit reduced charge separation effects which is expected to lead to improved optoelectronic properties, and are compatible with existing technologies.

In addition, these materials allow for both ease of p-type doping (huge issue with III-Vs) as well as band gap tunability via cation disorder and compositional control in contrast to binary III-Vs which suffer from miscibility issues. This project aims to establish a systematic process of ternary pnictide CQD synthesis and thin-film deposition of assemblies of CQDs, accompanied by complementary physical, spectroscopic and analytic characterization (both in-situ and ex-situ) techniques to elucidate the structure (order/disorder phases and defects), optical (quantum confinement) and electronic properties and provide feedback and guidance on the effects of synthesis conditions and crystallite size on film performance.

Thus, this close-knit coupled synergistic feedback loop of synthesis-structure-property-performance provides a detailed understanding of the defect structure and optoelectronic properties of II-IV-V2 CQDs. The project has three interrelated objectives and tasks: (1) Synthesis of ternary II-IV-V2 (ZnSnP2) CQDs, (2) Modulation of disorder and intrinsic defect concentration in ternary pnictide CQDs, and (3) Structural, optical and electrical characterization of pnictide CQDs.

Efforts are directed to integrate all these tasks simultaneously and synergistically to enable crucial breakthroughs in the materials science and engineering of II-IV-V2 based semiconductor nanostructures.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.