Title: Understanding Charge Transport in Lead-Halide Perovskite

Speaker: Dr. Satyaprasad P Senanayak, Cavendish Laboratory, University of Cambridge, UK

Venue: IOP Lecture Hall

Date: 2017-Jan-23 16:00:00

Abstract: Lead halide perovskite materials have caught lot of attention because of its usage in developing novel photovoltaics with effeciencies exceeding 22%. This level of optoelectronic performance has been possible due to clean band-gap, low disorder and various interesting properties. Despite the development of high efficiency optoelectronic devices, clear understanding of the charge transport and scattering mechanism has not yet been understood. Field effect transistors are an effective way to understand the charge transport mechanism. In the talk, I will describe the development of first room temperature operating field effect transistor with lead iodide perovskite through a combination of material and device engineering. Fundamental understanding of the various scattering mechanisms involved in the charge transport physics is then development through a combination of electrical and spectroscopic investigation [1]. The next part of the talk is on understanding the charge transport of polymer semiconductors. With suitable chemical design, interface and device engineering it was possible to approach disorder free transport in these inherently amorphous materials. Furthermore, a range of strategies would be discussed which allow flexible polymer logic circuits with with switching speed of 10 MHz, operating at 1 V and have a power consumption as low as 10 nW. These characteristics make the flexible polymer devices to have performance comparable or better than a-Si devices[2-3]. References: 1. Satyaprasad P Senanayak, Richard Friend, Henning Sirringhaus et.al.; Science, AAAS (Accepted). 2. Satyaprasad P Senanayak and Narayan K.S; Adv. Funct. Materials, 24, 22, 3331,2015. 3. Satyaprasad P Senanayak and Narayan K.S; Phys. Rev. B, B 91, 115302, 2016.

Title: Spintronics with 2D materials heterostructures

Speaker: Prof. Saroj Prasad Dash, Chalmers University of Technology, Gothenburg, Sweden

Venue: IOP Lecture Hall

Date: 2017-Jan-24 16:00:00

Abstract: Exploiting the spin degrees of freedom of electrons in solid state devices is considered as one of the alternative state variables for information storage and processing beyond the charge based technology. We have shown that the main stream semiconductor, silicon, has great potential with creation and detection of spin polarization up to room temperature [1,2,3]. However, one of the primary challenges in this field is the transport and manipulation of spin polarization. In this regard, two-dimensional (2D) atomic crystals provide a large class of materials proposed to be important for spintronics. Recently, we demonstrated a long distance spin transport over 16 µm and spin lifetimes up to 1.2 ns in large area CVD graphene at room temperature [4]. In order to achieve an efficient spin injection into graphene, we used h-BN tunnel barriers with large tunnel spin polarization up to 65 % at room temperature [5]. Recently, we demonstrated all–electrical spin field effect transistor (spin-FET) by employing graphene/MoS2 heterostructures at room temperature [6]. We further electrically detected novel spin current in topological insulators due to spin-momentum locking phenomenon at room temperature [7]. These findings open a platform for exploring novel spin functionalities in 2D materials heterostructures and understanding the basic phenomenon control their behavior. [1] SP Dash, S Sharma, RS Patel, MP de Jong, R Jansen; Nature 462 (7272), 491 (2009). [2] R Jansen, BC Min, SP Dash; Nature materials 9 (2), 133 (2010). [3] SP Dash et al., Physical Review B 84 (5), 054410 (2011). [4] MV Kamalakar, G. Chris, A Dankert, SP Dash; Nature Communication, 6, 6766 (2015). [5] MV Kamalakar, A Dankert, P. Kelly, SP Dash; Scientific Reports, 6, 21168 (2016). [6] A Dankert, SP Dash; arXiv:1610.06326 (2016). Under review in Nature Nano. [7] A Dankert, J. Geur, MV Kamalakar, S Charpentier, SP Dash; Nano Letters 15 (12) 7976 (2015).