Abstract
Lead halide perovskites are strong candidates for high-performance low-cost photovoltaics, light emission, and detection applications. A hot-phonon bottleneck effect significantly extends the cooling time of hot charge carriers, which thermalize through carrier–optic phonon scattering, followed by optic phonon decay to acoustic phonons and finally thermal conduction. To understand these processes, we adjust the lattice dynamics independently of electronics by changing isotopes. We show that doubling the mass of hydrogen in methylammonium lead iodide by replacing protons with deuterons causes a large 20 to 50% softening of the longitudinal acoustic phonons near zone boundaries, reduces thermal conductivity by ~50%, and slows carrier relaxation kinetics. Phonon softening is attributed to anticrossing with the slowed libration modes of the deuterated molecules and the reduced thermal conductivity to lowered phonon velocities. Our results reveal how tuning the organic molecule dynamics enables control of phonons important to thermal conductivity and the hot-phonon bottleneck.
| Original language | English |
|---|---|
| Article number | eaaz1842 |
| Journal | Science Advances |
| Volume | 6 |
| Issue number | 31 |
| DOIs | |
| State | Published - Jul 2020 |
Funding
We thank Y. Ma for setting up the initial transient absorption spectroscopic apparatus and providing maintenance to the laser system. Funding: The neutron scattering work by M.E.M. and R.P.H., the calorimetry measurements by A.F.M., and the transient absorption measurements by C.H. were supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division under contract no. DE-AC05-00OR22725. This research used resources at the HFIR and SNS, DOE Office of Science User Facilities operated by the Oak Ridge National Laboratory. M.Ah. acknowledge the support from the U.S. Department of Homeland Security under grant no. 16DNARI00018-04-0. Deuterated materials were synthesized at the Center for Nanophase Materials Sciences (CNMS), which is a DOE Office of Science User Facility. Thermal diffusivity measurements by H.W. were supported by DOE EERE Vehicle Technology Office under the Materials Technology program. Phonon calculations led by Y.C. and M.As. were supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division under contract no. DEAC02-05-CH11231 within the Materials Project program (KC23MP).