Research

Nanoscale Materials to Solve Next Generation Challenges

The challenges facing us today are immense, and nanomaterials have shown great promise to aid in their solutions. Yet individual material systems often have significant drawbacks that prevent successful adaptation. We seek to unite material systems to build nanoscale systems where we control the flow of light, energy, and spin. By combining and understanding these material systems, we aim to uncover unique strengths and physics that are unachievable by individual systems alone, finding solutions to the challenging problems facing us.

Photon Energy Conversion

The ability to convert the energy of photons can open up exciting avenues in a wide variety of applications for both downconversion (converting one high energy photon to two low energy photons) and upconversion (converting two low energy photons to one high energy photon). We study the fundamentals of these processes, and how those fundamentals can impact their applications in several fields, including:

Photovoltaics: Solar cells are fundamentally limited by the sunlight that falls upon them. Photons with energy greater than the bandgap lose that excess energy to heat, while photons with energy less than the bandgap are not absorbed. Downconversion allows for harvesting of that excess energy by generating two electron-hole pairs for every incident photon, while upconversion allows for the harvesting of photons below the bandgap energy. Taken together, these can lead to substantial gains in the harvestable solar spectrum. We are working to implement these technologies into high-performance solar cells towards a new generation of photovoltaic performance.

Volumetric 3D Printing: Within the context of stereolithography, it is difficult to deliver blue light past the surface of a 3D printing resin, making volumetric 3D printing extremely challenging. Triplet fusion upconversion nanocapsules allows us to print by focusing low energy light to generate blue light only where the light is most intense. This blue light is absorbed by a photoinitiator and ultimately allows us to print anywhere within a vat - not simply at the surface. Our tunable, proof of principle upconversion-facilitated 3D printing platform will allow us to access a diverse set of materials and form factors.

Night vision: The ability to passively upconvert near infrared photons to visible wavelengths would allow for compact, simple night vision units without the need for bulky electronics or batteries. We are studying thin-film upconversion systems to deliver materials that perform at high efficiencies and low input power.

Biological sensing and activation: Upconversion allows for the local generation of high energy visible light from a penetrating infrared beam, crucial for biological applications ranging from sensing to optogenetics to drug synthesis. Key to this process is the ability to introduce upconversion systems in a biocompatible method that maintains high upconversion performance. We are working to develop and apply these systems at the nanoscale.

Optoelectronic Devices

Converting between light an electricity efficiently is a fundamental need in a wide variety of processes, including energy generation, lighting, displays, communications, and sensing. We study nanomaterials to build the next generation of stable and efficient optoelectronic devices.

Perovskite LEDs: In the last decade, metal halide perovskites have shown great promise for next-generation light emission due to their excellent optoelectronic properties including optical band gap tunability, sharp color purity, and facile solution processability. Within the last few years, green and red perovskite LEDs (PeLEDs) have achieved external quantum efficiencies on par with organic LEDs, however blue emission and operational stability across the visible spectrum remain key challenges. To tackle the challenges associated with bluer emission, we are exploring novel device structures and exploring  wide-bandgap semiconductors. To solve the operational stability issues, we are examining the role of the nanoscale materials and novel device architectures to identify and eliminate modes of degradation. From a materials perspective, we focus on precise synthesis and surface engineering of inorganic nanocrystals for next-generation solid-state optoelectronic applications. We seek to improve the optical properties and long-term stability of the nanocrystals through different strategies such as surface ligand tuning and composition control.

Perovskite lasers: Lead halide perovskite materials show great potential as gain media due to their attractive optoelectronic properties. These perovskite materials are competitive with inorganic and organic semiconductor laser gain media, with some key advantages such as their ability to be solution processed. Through cavity design and engineering and material innovations, we are working towards developing enhanced perovskite lasers with the ultimate goal of making strides towards electrical pumping of these exciting materials.