Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session J21: Photovoltaic Materials and Phenomena |
Hide Abstracts |
Sponsoring Units: GERA Chair: Jeffrey Owrutsky, United States Naval Research Laboratory Room: 302 |
Tuesday, March 3, 2020 2:30PM - 2:42PM |
J21.00001: Role of defects in MAPbI3 to modulate optical absorption, and solar efficiency Pooja Basera, Saswata Bhattacharya Methylammonium lead halide (MAPbI3) perovskite has emerged as one of the frontier optoelectronic semiconductors. To avoid lead-toxicity, the role of Sn-substitution and Pb-vacancy (Pb-■) is addressed in regulating the stability and solar cell efficiency of MAPb1-X-YSnX■YI3 perovskite using hybrid density functional theory (DFT). We find, to reduce the Pb-content from pristine MAPbI3, Sn-substitution has favorable thermodynamic stability than Pb-■. High optical absorption coefficient (red shifted) and maximum solar cell efficiency are obtained in |
Tuesday, March 3, 2020 2:42PM - 2:54PM |
J21.00002: Engineering Photovoltaic Response of 2D Ruddlesden-Popper Perovskite using Plasmonics. Yashika Gupta, ANSHUMAN KUMAR Organic-Inorganic Lead based perovskite solar cells offer a promising alternative to present day Si-solar cell, reaching an efficiency of almost 25% in a span of less than ten years. However, perovskite based cells still face stability and toxicity issues due to their constituents elements like organic molecules (Methylammonium, Butylammonium etc.) and heavy metal ions (Lead) thus limiting it’s prospects towards commercialization. A lot of efforts have been made towards improving the stability of these lead base perovskites to improve their stability by introducing a heavy metal cation into conventional perovskite materials to generate a 2D structure, called Ruddlesden-Popper Perovskite with improved stability than the conventional 3D perovskites. But the issue of Lead toxicity remains. In this work, we propose use of plasmonics as an efficient method to improve the efficiency 2D Ruddlesden Popper perovskite solar cell. The use of plasmonic structures will result in improved light harvesting in the cell while keeping the perovskite layer thickness to minimum and hence reducing the toxic content of the cell giving it a fighting chance for practical applications. |
Tuesday, March 3, 2020 2:54PM - 3:06PM |
J21.00003: Scaling law for excitons in layered 2D perovskites systems: Dion-Jacobson (DJ) phases and Alternating Cation in the Interlayer space (ACI) phases Hao Zhang, Siraj Sidhik, Wenbin Li, Jacky Even, Jean-Christophe Blancon, Aditya Mohite Layered two-dimensional (2D) hybrid perovskites are emerging types of semiconductor quantum wells (QWs) with highly promising opto-electronic applications. These solution-processed materials offer tunability of opto-electronic properties, which can be achieved by varying quantum well thickness (n-value). For instance, our previous work has demonstrated the scaling behavior of excitons with different quantum well thickness in Ruddlesden-Popper (RP) Perovskites. Besides the well-studied RP perovskites, there’re other crystal structures such as Dion-Jacobson (DJ) and Alternating Cation in the Interlayer space (ACI) phases, whose intrinsic exciton and charge carrier properties still remain unrevealed. Here, using optical spectroscopy, we perform detailed studies of the optical and electronics properties on DJ and ACI systems, such as exciton fine structure, electron-phonon coupling and defect states, and demonstrate their scaling behavior with quantum well thickness. These results will bridge the gap between optical properties of 2D and 3D perovskite crystals, leading to better design of opto-electronics devices. The tendency of how different 2D perovskites phases merge into unique 3D perovskite will give us a deeper understanding of the fundamental physics of perovskite materials. |
Tuesday, March 3, 2020 3:06PM - 3:18PM |
J21.00004: Increasing open-circuit voltage in CdTe solar cells through passivation of the previously inaccessible front interface Deborah McGott, Yegor Samoilenko, Brian Fluegel, Colin Wolden, Matthew Reese Cadmium telluride (CdTe) is the leading commercialized thin-film photovoltaic (PV) technology with over 25-GW-scale annual production and record device efficiency of 22.1%. However, a major obstacle to achieving higher efficiencies in CdTe is a stubbornly low open-circuit voltage (VOC) of ~800-900 mV despite having a near ideal bandgap of 1.45 eV. Surface passivation, particularly of the front interface, is thought to be critical to reduce electron-hole recombination and increase VOC. The front interface, however, is buried under microns of material during standard growth of superstrate CdTe and made inaccessible. Here, we use a novel thermo-mechanical liftoff technique to expose the buried front interface, then passivate the surface to improve minority carrier lifetime measured using time-resolved photoluminescence (TRPL). We then complete the device by depositing a transparent front contact to correlate VOC changes in the front interface and minority carrier lifetime. |
Tuesday, March 3, 2020 3:18PM - 3:30PM |
J21.00005: Valley Photovoltaics: Experimental Evidence for a Practical Route towards the Realization of the Hot Carrier Solar Cell Kyle R Dorman, Hamidreza Esmaielpour, David K Ferry, Tetsuya D Mishima, Michael B Santos, Vincent R. Whiteside, Ian R Sellers Hot carrier solar cells offer the potential to increase the efficiency of single gap solar cells beyond 60%. Here a new and viable route is proposed where photoexcited electrons are scattered to and collected from the L and X valleys. We demonstrate proof-of-principle results for an InGaAs/AlInAs heterojunction solar cell that shows an operating voltage (~1.4 eV) in excess of the InGaAs absorber bandgap (0.75 eV) under 1-sun AM 1.5G. Hot carriers are confirmed in simultaneous monochromatic current–voltage and photoluminescence measurements. Hot carrier operation in this simple commercially mature system is driven by the transfer, storage, and extraction of hot carriers in the satellite valleys of InGaAs. Combining intervalley scattering and the Gunn Effect allows the majority of photoexcited electrons to be harnessed with voltages defined by the upper valley separation, and thus an optimized system would exceed the Shockley-Queisser limit for a single bandgap solar cell. A mismatch in the valley degeneracy across the n+-AlInAs/n-InGaAs interface currently limits the performance, but a clear route to the realization of such a device in traditional III-V technologies is presented. |
Tuesday, March 3, 2020 3:30PM - 3:42PM |
J21.00006: PMEG and PMPG (plasmonic multi-electron and multi-photon generation) for PV Linden Hayes, Lingpeng Luo, Cong Chen, Krzysztof Kempa, Jinwei Gao, Frank Shih-Yu Tsung, Michael Naughton We have recently shown that by embedding nanoparticles possessing properly-tuned plasmonic resonances in the small gap semiconductor absorber of a solar cell that it is possible to achieve significant plasmonic multi-electron generation (PMEG)[1] . Synthesis efforts are underway to construct a perovskite-nanoparticle system in order to experimentally verify the viability of PMEG to increase the efficiency of the solar cell. |
Tuesday, March 3, 2020 3:42PM - 3:54PM |
J21.00007: Suppressing deep-trap formation in Cu2ZnSnS4-based solar cells Robert Wexler, Sai Gautam Gopalakrishnan, Emily Carter Cu2ZnSnS4 (CZTS) is a cheap, nontoxic, easy-to-synthesize, and stable solar cell absorber material. Despite these advantages over Si, GaAs, CdTe, CuInxGa1-xSe2, and hybrid perovskites, CZTS-based solar cells are plagued by low efficiencies (12.6%) compared to the Shockley-Queisser limit (33.7%). This 21.1% efficiency deficit was suggested recently to be due to the formation of defect clusters involving the SnZn antisite, which induces deep-trap states and therefore promotes carrier recombination. In this talk, we present density functional theory calculations of defect thermodynamics to show that these deep-trap defect clusters can be suppressed in CZTS via Ge- and Se-codoping. Additionally, we will describe an electrostatic mechanism for the suppression of deep defects by Ge that can be readily applied to other kesterite-type absorber materials and therefore used to design next-generation CZTS-inspired solar cells. |
Tuesday, March 3, 2020 3:54PM - 4:06PM |
J21.00008: A low-temperature-low-intensity study of flexible CIGS solar cells Hadi Afshari, Brandon Durant, Collin Brown, Khalid Hossain, Dmitry Poplavskyy, Ian R Sellers Commercially available lightweight and flexible CIGS solar cells are investigated for their performance under low intensity low temperature (LILT) conditions governing outer planets Mars, Jupiter, and Saturn. Current density-voltage under varying temperatures and illumination intensities, including concentrated solar, as well as electroluminescence measurements is performed to investigate the effects of conditions in deep space. A barrier to minority carrier extraction is observed and attributed to the acceptor rich defect layer near the CIGS absorber/ CdS buffer interface. The effect of this barrier on power generation is presented and shown to decrease after light soaking, due to a transition between the so-called relaxed to metastable states. The power conversion efficiencies are shown to be higher for LILT conditions compared to terrestrial application. |
Tuesday, March 3, 2020 4:06PM - 4:18PM |
J21.00009: Interfacial Properties of Solar Energy Materials from DFT: P3HT/ZnO and CdS/Graphene Leah Bendavid, Liat H. Kugelmass, Austin Atsango, Reid W. Smith We present two projects that demonstrate how computational quantum chemistry is used to better understand materials for solar energy applications. In the first project, we use density functional theory (DFT) to examine the P3HT/ZnO solar cell and the mechanism by which interfacial modification with PCBA and doping with Sr enhances photovoltaic efficiency. We find that the enhancement in photovoltaic efficiency is not due to changes in equilibrium structures or adhesion strengths. Rather, the impacts of Sr-doping and PCBA are linked to changes to the energy level alignments. In the second project, we focus on CdS/graphene photocatalytic interfaces. Using DFT calculations, we study the interfacial properties of CdS(0001)/graphene and a CdS/graphene bilayer, and examine whether doping with B/N can strengthen interfacial adhesion. The CdS/graphene bilayer is found to exhibit high interplanar distances and low adhesion energies, characteristic of dispersion-dominated interfacial adhesion. Doping graphene does not significantly modify the strength of adhesion, but it does enable modulation of the band edge and Fermi level alignments. The CdS(0001)/graphene interface is found to be similarly adhered via dispersion interactions, but here, doping with B strengthens interfacial adhesion. |
Tuesday, March 3, 2020 4:18PM - 4:30PM |
J21.00010: Polymer solar cell incorporating PEDOT:PSS films and MEH-PPV nanopillars Archana Kumari Poly[2-methoxy-5-(2-ethylhexyloxy)-1.4-phenylenevinylene] (MEH-PPV) is an attractive polymer for organic solar cells which were fabricated with spin coating technique using capillary force through the pores in to the channels of the alumina templates on the Glass/ITO substrates. The nanopillars were studied using UV-Vis absorption spectroscopy and found an enhanced absorption as compared to same thickness of MEH-PPV films. Organic solar cells will be fabricated with structures as Glass/ITO/ TiO2/PEDOT:PSS/ MEH-PPV nanopillars/Al, where MEH-PPV acts as an electron donor and TiO2 semiconductor material is used as an acceptor in polymer solar cell. PEDOT:PSS can improve performance by enhancement of hole collection, exciton diffusion and photocarrier transport. Surface morphology of the nanopillars in solar cell will be studied using Scanning Electron Microscopy, and various other characterization techniques such as UV-Vis spectroscopy, PL spectroscopy, energy dispersive X-ray spectroscopy and atomic force microscopy will be used. The performance of the solar cells will be determined by I-V characterization. Optimization of the dimensions of the nanopillars and thickness of the film will be done to obtain maximum efficiency of the devices. |
Tuesday, March 3, 2020 4:30PM - 4:42PM |
J21.00011: Hot carrier dynamics in Quantum Well Solar Cells (Thermal Photon Gain) Brandon Durant, Keith Barnham, Vincent R. Whiteside, Ian R Sellers Quantum well solar cells (QWSCs) have been shown to inhibit hot carrier thermalization relative to bulk materials and have therefore stimulated significant interest as a potential absorber region in third generation hot carrier solar cells. Investigations of high quality InGaAs/GaAsP QWs in GaAs p-i-n solar cells have recently alluded to the possibility of hot carrier extraction in device structures through the measurement of a diode ideality factor of n < 1. In order to prove the carriers extracted in these systems are in fact “hot,” simultaneous current density-voltage (JV) and photoluminescence (PL) measurements are performed to directly compare the carrier dynamics and photovoltaic performance in such devices. Several transitions complicate the PL spectra of QWs making determination of the carrier temperature via fitting of the high energy tail using simple Planck’s law methods insufficient. Therefore, full spectral fitting is performed in order to extract the carrier temperature while considering the occupation of higher energy states in the QWs, which is then related to ideality factor determined in electrical measurements. |
Tuesday, March 3, 2020 4:42PM - 4:54PM |
J21.00012: Giant Photovoltaic Effect in Magnetic Materials Oles Matsyshyn, Inti Sodemann We investigate a rectification process present in materials that break both inversion and time reversal symmetries. At second order in electric fields, this effect is inverseley proportional to the relaxation rate, and, therefore, the rectified current would be infinity in a "naive" ideal clean and zero temperature limit. Employing Floquet theory, we show, however, that there is a non-perturbative correction in the electric field strength that regularises this divergence, but, which ultimately leads to a giant photo-current generation. Therefore, this effect offers a promising alternative paradigm for solar cell technologies. |
Tuesday, March 3, 2020 4:54PM - 5:06PM |
J21.00013: Thermodynamics of Photovoltaic Conversion with Nonreciprocal Processes Andrei Sergeev, Kimberly Sablon Nonreciprocal photon and electron processes can violate Kirchhoff’s law, detailed balance, and chemical equilibrium in the system of electrons and phonons. As the fundamental Shockley – Queisser limit of photovoltaic conversion is directly based on detailed balance, nonreciprocal processes can improve the efficiency beyond the Shockley – Queisser limitation. We derived thermodynamic limits of efficiency of photovoltaic converters with nonreciprocal processes and consider various realization of nonreciprocal converters. We demonstrate that even dissipative nonreciprocal processes can increase the conversion efficiency beyond the Shockley – Queisser limit. The thermodynamic theory is applied to solar energy conversion, laser power beaming, and thermophotovoltaic conversion. |
Tuesday, March 3, 2020 5:06PM - 5:18PM |
J21.00014: Direct Observation of shift and ballistic photovoltaic currents Aaron Burger, Radhe Agarwal, Alexey Aprelev, Edward Schruba, Alejandro Gutierrez-Perez, Vladimir M. Fridkin, Jonathan E Spanier The quantum phenomenon of shift photovoltaic current was predicted decades ago, but this effect was never observed directly because shift and ballistic currents coexist. The atomic-scale relaxation time of shift, along with the absence of a photo-Hall behavior, has made decisive measurement of shift elusive. Here, we report a facile, direct-current, steady-state method for unambiguous determination of shift by means of the simultaneous measurements of linear and circular bulk photovoltaic currents under magnetic field, in a sillenite piezoelectric crystal. Comparison with theoretical predictions permits estimation of the signature length scale for shift. Remarkably, shift and ballistic photovoltaic currents under monochromatic illumination simultaneously flow in opposite directions. Disentangling the shift and ballistic contributions opens the way for quantitative, fundamental insight into and practical understanding of these radically different photovoltaic current mechanisms and their relationship. |
Tuesday, March 3, 2020 5:18PM - 5:30PM |
J21.00015: Bulk photovoltaic effect induced by elliptically-polarized light Lingyuan Gao, Andrew Marshall Rappe Shift current has been considered as one of the major orgins for bulk photovoltaic effets. In this study, using time-dependent perturbation theory, we investigate the light polarization effect on shift current. We give a general formula for shift current indcued by elliptically-polarized (EP) light, which represents the most general form of a polarized light. By using a two-band model widely applied in 2D materials, we calculate the EP shift current quantitatively, and compare it with the linearly-polarized shift current and circularly-polarized injection current. |
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