Speaker：Dr. Ti Wang, Purdue University, USA
Invited by：Prof. Xiong Wei
Time：15:00-16:30, September 3, 2018
Venue: A101
Abstract:
Slow cooling of hot polarons resulting from phonon bottleneck has been observed in perovskites, pointing toward the potential for harvesting hot carriers to overcome the Shockley-Queisser limit. Open questions remain on whether the high optical phonon density from the bottleneck impedes the transport of these hotpolarons. We present a direct visualization of hot polaron transport utilizing transient absorption microscopy. Remarkably, hot polaron diffusion does not suffer from but rather is enhanced by the presence of phonon bottleneck, opposite from what is observed in GaAs.
Compared to free carriers in perovskites, an electron and a hole bound together to form an exciton in organic semiconductors due to the large binding energy. A fast transport has been observed within the first few picoseconds which is often attributed to the large spatial coherent size of the exciton. However, critical details such as how far excitons could move via coherent coupling and how an exciton can overcome its strong binding and dissociate into free carriers at an interface remain unclear. Time-resolved two photon photoemission spectroscopy is used to study the exciton transport range and electronic coherent sizes of the manifold of interfacial CT states, and capture the temporal dynamics of these CT states.
Biography：
Dr. Ti Wang received his Ph.D degree in 2013 at Wuhan University. After the Ph.D study, he joined University of Kansas and Purdue University for his postdoctoral research. During the postdoctoral research, his works focused on ultrafast pump-probe spectroscopy to study the ultrafast carrier dynamics, transport and separation in photovoltaic semiconductors. He published more than 30 SCI research articles, such as Journal of the American Chemical Society、ACS Nano、Advanced Functional Materials、ACS Energy Letters、The Journal of Physical Chemistry Letters、Physical Review Applied、Physical Review B（Rapid communication. Meanwhile, he also has done a lot of oral presentations on international conferences.
