Speaker: Deep Jariwala, Electrical and Systems Engineering, University of Pennsylvania

Abstract: High efficiency inorganic photovoltaic materials (e.g., Si, GaAs and GaInP) can achieve maximum above-bandgap absorption as well as carrier-selective charge collection at the cell operating point. But thin film photovoltaic absorbers have lacked the ability to maximize absorption and efficient carrier collection, concurrently often due to due to surface and interface recombination effects. In contrast, Van der Waals semiconductors have naturally passivated surfaces with electronically active edges that allows retention of high electronic quality down-to the atomically thin limit. This presents interesting opportunities for remote power and applications that require high-specific power in place of cost or efficiency. This webinar will focus on a review of advances in photovoltaics based on 2D semiconductors to date for the first part In the second part, I will show some of our own results in this space which have been dedicated to systematically address the three major engineering challenges for efficient photovoltaics: 1. Light absorption 2. Carrier collection 3. Band alignments. I will present our experimental demonstration of near-unity light confinement in ultrathin (less than 15 nm) Van der Waals semiconductors (MoS2, WS2 and WSe2) leading to nearly perfect absorption.1 I will further present the fabrication and performance of our, broadband absorbing, heterostructure photovoltaic devices using sub-15 nm TMDCs as the active layers, with record high quantum efficiencies.2 I will then present ongoing work on addressing the key remaining challenges for application of 2D materials and their heterostructures in high efficiency photovoltaics3 which entails engineering of interfaces and open-circuit voltage4 as well as on going work on novel materials and light trapping5 in monolayers. I will conclude by giving a broad perspective of future work on 2D materials from fundamental science to applications. References: 1. Jariwala, D.; Davoyan, A. R.; Tagliabue, G.; Sherrott, M. C.; Wong, J.; Atwater, H. A. Nano Letters 2016, 16, (9), 5482-5487. 2. Wong, J.; Jariwala, D.; Tagliabue, G.; Tat, K.; Davoyan, A. R.; Sherrott, M. C.; Atwater, H. A. ACS Nano 2017, 11, 7230–7240. 3. Jariwala, D.; Davoyan, A. R.; Wong, J.; Atwater, H. A. ACS Photonics 2017, 4, 2692-2970. 4. Wu, F.; Li, Q.; Wang, P.; Xia, H.; Wang, Z.; Wang, Y.; Luo, M.; Chen, L.; Chen, F.; Miao, J.; Chen, X.; Lu, W.; Shan, C.; Pan, A.; Wu, X.; Ren, W.; Jariwala, D.; Hu, W. Nature Communications 2019, 10, (1), 4663. 5. Brar, V. W.; Sherrott, M. C.; Jariwala, D. Chemical Society Reviews 2018, 47, (17), 6824-6844.