Congreve Lab, Prof. Dan Congreve
Daniel Congreve leads the Congreve Lab in the Department of Electrical Engineering at Stanford University. The Congreve Lab seeks to better understand the physics of nanoscale materials and use that knowledge to build more efficient devices such as LEDs, photovoltaics, and many others. The Congreve Lab pursues interdisciplinary research with members from Electrical Engineering, Physics, Chemistry, and Material Science backgrounds.
Broadly, the goal of research in the Congreve Lab is to use 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.In addition to research, the members of the Congreve Lab pursue several mentorship opportunities (REU, SURF, etc.) and DEI efforts. Follow us on Twitter to get updates on our pursuits.
Photon Energy Conversion
As for the specific area of research, Photon Energy Conversion is one of the main focuses of the lab. 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 and micelles 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.
Micro/nano-scale printing
Aside from volumetric 3D printing, another unique opportunity that triplet fusion upconversion can provide is facilitating micro/nano scale 3D printing. Since triplet fusion upconversion is a two-photon absorption process exhibiting a threshold behavior to generate upconverted light, one can take advantage of this to precisely control the polymerization in z-direction by operating the printing power in the quadratic regime. Compared to other cutting-edge 3D printing technologies, 3D printing via triplet fusion upconversion shows distinct potential to achieve high-resolution, low-power, high-speed, and scalable micro/nano scale volumetric 3D printing.
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
Another research avenue we focus on is optoelectronic devices. Converting between light and 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 violet and UV emission remains challenging. To tackle the challenges associated with bluer emission, we are exploring novel device structures and exploring wide-bandgap semiconductors.
Operational stability of PeLEDs
PeLEDs suffer from low operational stability across all wavelength regimes. 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.
