Lead halide perovskites possess the electrical and optical properties of conventional semiconductors, but unlike most semiconductors they can be prepared by simple inexpensive methods including deposition from solution. They have attracted intense worldwide research activities for use in next generation solar cells, light emitting diodes, scintillators for detection of X-rays, and many other applications. Their biggest liability is the toxicity that comes from the presence of lead. In this research project we set out to study and develop lead-free halide double perovskites and evaluate their properties.

Over the course of the project, we found that double perovskites containing chloride are relatively straightforward to synthesize, but those containing iodide are unstable and could not be made by any known synthesis route. Given the larger band gaps of the chloride compounds this discovery shifted the focus of the research toward a search for new phosphors, materials that play a key role in lighting technologies. Four new phosphors were developed to convert near UV light into visible light, all of them without relying on rare-earth ions. Cs₂NaBiCl₆:Mn²⁺ and Cs₄Cd_1−xMn_xBi₂Cl₁₂ both emit red light, Cs₂NaInCl₆:Sb³⁺ emits blue light, and Cs₂AgIn_1−xBi_xCl₆ has a broad emission spectrum that contains most colors of visible light. Unlike most commercial phosphors these materials can be prepared from low temperature solution routes. Proof of concept white lights driven by high efficiency near-UV LEDs were constructed using the newly developed phosphors. Electric lighting is one of the largest consumers of energy, with residential and industrial lighting accounting for ~15% of the total United States electricity consumption in 2019. It is hoped that this research might spur new activity in the development of phosphors for this critically important technology. 

The effects of structural distortions on the optical properties of lead halide perovskites were also examined and it was found that the band gap can be systematically increased by using a smaller charge compensating cation in the 12-coordinate cavity of the perovskite structure. The compositional space of the double perovskite family was expanded to include hybrid organic-inorganic layered perovskites.  

The funds provided by this grant supported in part the training of five undergraduate and four graduate students, three of whom have successfully completed their PhD and the fourth is on pace to finish in late 2022. A semester long series of teaching laboratories were developed and implemented in the second semester general chemistry courses taken by chemistry majors and honors students. These labs introduce concepts such as crystallography, X-ray diffraction, semiconductors, and materials synthesis to first year university students. Over the course of the grant approximately 800 students matriculated through this laboratory experience. This will not only inspire students to pursue more traditional research opportunities while at Ohio State University it will help to create a more informed populace that can critically assess the value and new directions in energy related research.

Last Modified: 01/17/2022
Modified by: Patrick M Woodward