Understanding processing and device function of metal halide perovskite thin film solar cells
Abstract
This ONR Young Investigator Program proposal describes a comprehensive study on an emerging class of thin film photovoltaic materials - hybrid organic-inorganic metal halide perovskites - which are rapidly gaining efficiency, but which currently lack crucial knowledge of processing, semiconductor and device physics that hold back the ability to realize their full potential. Thus, we propose to answer fundamental yet key unresolved questions facing metal halide perovskite film formation, electronic and optical properties, and device physics. Because our proposed measurements of optical and electrical properties, as well as solar cells, require samples that are flat, pinhole free, and thickness-tunable, we have outlined a series of experiments to realize these goals. Along with the impressive gains in perovskite solar cell efficiency have come a myriad of processing approaches with varying degrees of success. We propose here to unify these various approaches within the framework of sol-gel processing, a powerful science that emerged decades ago from the processing of oxides such as silica. Our preliminary data show that the solution processing of metal halide perovskites shows all of the hallmarks of sol-gel processing, and allows us to utilize sol-gel engineering to achieve ultrasmooth films of metal halide perovskites with roughness <2 nm. This has also allowed us to identify intrinsic problems with the use of “good” solvents for these materials, in that the reaction and crystallization processes are too coupled. To decouple them, we propose a novel approach to film formation from dispersion of metal halide perovskite nanoparticles in nonsolvents, an approach that promises substantial benefits to upscaled depositions at large areas as well as the ability to access the to-date unknown perovskite/perovskite heterojunction. Through a combination of Hall, photoluminescence, and internal photoemission measurements, we intend to comprehensively understand heterojunction and interface behavior of perovskite thin films with both device relevant materials (e.g. organic semiconductors and transition metal oxides) as well as, unprecedentedly, other metal halide perovskites. This will provide the knowledge required to design and predict behavior at interfaces and heterojunctions with other materials, information that is currently missing. In terms of perovskite/perovskite heterojunctions, such interfaces have never been prepared or characterized, and promise significant gains in device performance and functionality. In the end, a clear demonstration of the influence of the substrate, in particular its work function and carrier concentration, on the majority carrier type and carrier concentration of the overlying perovskite film, will be an essential step toward fully understanding the carrier generation mechanisms in the solar cell. Finally, we propose measurements on solar cells to ascertain the exact device physics at play, in particular whether or not the photocurrent is primarily collected via drift in an electric field, as would be the case for a p-i-n solar cell, or via diffusion, as would be the case for a p-n heterojunction. Answering this question will inform the further development of perovskite thin film solar cells to maintain momentum for the rapid efficiency increases observed in the last few years. The PI has the proper set of expertise and the track record to complete the proposed work and make an impact in this burgeoning solar cell field. Overall, this ONR Young Investigator Program work plan is meant to allow the PI to remain at the forefront of thin film solar cell technology and push the limits of what is possible within this Naval-relevant topic.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jan 04, 2017
- Source ID
- N000141712005
Entities
People
- Barry P Rand
Organizations
- Office of Naval Research
- Trustees of Princeton University
- United States Navy