Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session L47: Photovoltaics -- Solar Energy Conversion IIFocus
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Sponsoring Units: GERA Chair: John Mintmire, Oklahoma State University-Stillwater Room: BCEC 213 |
Wednesday, March 6, 2019 11:15AM - 11:27AM |
L47.00001: Hybrid functional studies of electronic properties of Cu2MgSnS4 (CMTS) for photovoltaics Kin Fai Tse, Man Hoi Wong, Junyi Zhu Cu2ZnSnS4 (CZTS) is a promising photovoltaic absorber material, efficiency is however largely hindered by potential fluctuation and band tailing problem due to abundance of defect and their complexes. Our previous work has establish CMTS should have a stable chemical potential range and desirable optical properties similar to CZTS. In this work, we examine the electronic properties of CMTS using HSE06 functional, our results shows 1) a general increase in formation energy in most defects except MgSn in CMTS, mainly due to the change of ground state structure, 2) qualitative similarity of defect thermodynamics and electronic properties in CMTS to CZTS and 3) identified CuMg as the main contribution to p-type carrier. These findings suggest CMTS may suppress potential fluctuation due to formation of detrimental CuZn+ZnCu defect complex in CZTS, and alleviate the band tailing near CZTS and CdS interface, and further confirm the feasibility of CMTS as an alternative absorber material to CZTS, suggesting potential for tuning. Implications to alloy with CZTS will be discussed. |
Wednesday, March 6, 2019 11:27AM - 11:39AM |
L47.00002: First-principles structural studies of polythiophene isomeric systems John Mintmire Recent experimental work has been reported for the synthesis of poly-ortho-thiophenes, in particular helical poly(5-alkyl-2,3-thiophene)s. These polythiophenes differ from the poly(3-alkyl-2,5-thiophene)s studied over for the past several decades as electroactive polymers similar to the polypyrroles, and which have had application in bulk heterojunction photovoltaics. We have carried out first-principles, density functional simulations for the electronic structure and total energy of a range of polythiophene systems using Gaussian-function-based orbitals in a band structure approach using helical symmetry. We have examined the hydrogen, methyl, ethyl, and propyl substituted poly(5-alkyl-2,3-thiophene)s and poly(3-alkyl-2,5-thiophene)s, optimizing the geometry as a function of twist angle in the helical backbone. We have also looked into other possible polymer conformations such as the poly(5-alkyl-2,4-thiophene)s. |
Wednesday, March 6, 2019 11:39AM - 11:51AM |
L47.00003: A New Family of Plasmonic Photocatalysts without Noble Metals Dongyang Wan, Bixing Yan, Xiao Renshaw Wang, Thirumalai Venky Venkatesan Efficient photocatalysis is important for sustainable energy. Recently, an unconventional photocatalyst based on intrinsic plasmon, called intrinsic plasmonic photocatalyst (IPP), seems promising for higher efficiency in hydrogen evolution1. This catalyst seems to benefit from the advantages of visible light absorption, plasmon-assisted hot carrier generation over conventional photocatalysts. Here, we report the relative hydrogen evolution efficiency under visible light irradiation of a family of IPP based on alkaline earth niobates (MNbO3 , where M=Ca, Sr or Ba), with efficiency of CaNbO3 > SrNbO3 > BaNbO3. The contributions of electron-phonon coupling time and solar energy absorption to the hydrogen evolution efficiency are identfied as keys based on our comprehensive characterization of carrier density (1022 cm-3), plasmon absorption, carrier dynamics and surface area. This study demonstrates a generic approach to create a family of IPP and validates the solar energy absorption of intrinsic plasmon as an additional knob to enchance the photocatalytic efficiency. |
Wednesday, March 6, 2019 11:51AM - 12:03PM |
L47.00004: Influence of microstructure on resistance, photovoltaic response and piezoelectric voltage of Colemanite Chandrima Chatterjee, Bhaskar Roy Bardhan Colemanite belongs to the class of prismatic monoclinic crystals. It is a hydrous compound and the water molecules contribute to conduction mechanisms at high temperature. The material contains interstitial and substitutional point defects which form intraband energy levels. These energy levels trap electrons and at high temperature the electrons gain enough energy to move to the conduction band. This phenomenon shows up as peaks in the current-voltage characteristics of colemanite. When excited with near ultraviolet light, colemanite exhibits ohmic resistance. The presence of photovoltaic microstructures such as grain boundaries, ferroelectric domains and others is responsible for this kind of behavior. The results show that colemanite may be used to generate higher photocurrent than conventional semiconductors. This opens up new possibilities of replacing semiconductors in photovoltaic device with colemanite. The piezoelectric response from different positions of colemanite varies in order of magnitude. These variations are due to the presence of point defects. The results may be used in the nondestructive testing of the uniformity of surfaces of piezoelectric crystals in general. |
Wednesday, March 6, 2019 12:03PM - 12:15PM |
L47.00005: Inexpensive Solar Tracking for Developing Regions Beth Parks A solar tracking system for photovoltaic cells was built and tested in sub-Saharan Africa. The cell was suspended from a mount, and weights were hung on the two ends. One of the weights was a water bucket with a controllable leak. The water bucket was hung from the east end of the cell, and the weights were adjusted so it was heavier in the morning. Over the course of the day, as it lost water, the cell rotated to track the sun. The system was tested for 20 days, and collected 32% more energy than would have been collected by a horizontal solar cell in the same location. The cost of the frame is less than the savings in purchasing a smaller PV cell, so it has the potential to make solar energy more affordable to households and small businesses in the developing world. |
Wednesday, March 6, 2019 12:15PM - 12:27PM |
L47.00006: Simulation-Optimized ZnSxSe1-x Contacts on Si for Photovoltaic Carrier-Selective Contacts Rebecca Glaudell, Harry Atwater ZnSxSe1-x films are promising materials for front carrier-selective contacts in silicon photovoltaics given their wide bandgaps and low resistivities compared to amorphous silicon, with the potential to capture more photo-generated current than a traditional heterojunction with intrinsic thin layer (HIT) solar cell. X-ray photoelectron and ellipsometric spectra of ZnSxSe1-x (x ranging from 0 to 1) films grown on Si by molecular beam epitaxy were used to measure band offsets of ZnSxSe1-x with respect to Si for purposes of accurate optoelectronic simulations of photovoltaic devices incorporating ZnSxSe1-x carrier-selective contacts. Further experimentally determined parameters including complex refractive index and resistivity were also included in the simulation of a HIT-style cell to determine the ZnSxSe1-x top contact mole fraction x, doping level, and thickness for optimal device performance. |
Wednesday, March 6, 2019 12:27PM - 12:39PM |
L47.00007: Modeling of PV/TPV devices using analytical solution of generalized Shockley – Queisser model Andrei Sergeev, Harry Hier, Christopher Mike Waits The generalized Shockley-Queisser (gSQ) model takes into account the frequency dependent absorption (emission), photon trapping and recycling, photocarriers multiplication, and nonradiative recombination processes. Exact analytical solution of gSQ model allows one to present the conversion efficiency and other photovoltaic (PV) and thermophotovoltaic (TPV) characteristics in convenient form via the Lambert W function, which is well approximated by logarithmic functions [1]. Analytical equations for useful energy, emission losses, thermal losses and optimal photocarrier collection time provide effective, convenient, and flexible tool for modeling of modern devices with effective photon trapping and recycling. We discuss analysis of experimental characteristics and optimization of PV/TPV devices based on gSQ solution. [1] Sergeev and Sablon, Exact Solution, Endoreversible Thermodynamics, and Kinetics of the Generalized Shockley-Queisser Model, Phys. Rev. Appl. 2018. |
Wednesday, March 6, 2019 12:39PM - 12:51PM |
L47.00008: Density Functional Theory calculations of optical properties of Hybrid Halide Perovskite Bio-Solar Cells Subhabrata Das, Bernardo Barbiellini, Ponisseril SOMASUNDARAN, Venkatesan Renugopalakrishnan The photovoltaic performance of hybrid halide perovskite is related to the atomic and electronic structure at the interface between the carrier generating perovskite layer and the electron transport layer (ETL). Based on ab-initio density functional theory (DFT) calculations, we studied the interfacing of the ETL layer, bacteriorhodopsin (bR) protein with Methylammonium lead triiodide CH3NH3PbI3 based organic-inorganic hybrid perovskite to fabricate Perovskite Biosolar Cells, which demonstrated a high ambient stability and an optical bandgap extending into the visible range. The dielectric spectrum of the Perovskite thin films is evaluated and validated with spectroscopic ellipsometry data. We further model the dielectric function according to the established Drude model with coupled harmonic oscillators. Our results agree well with reported data of the optical absorption coefficient and consistent with Kramers−Kronig transformations thus demonstrating band alignment between the protein and the perovskite. Hence, we comment on the structural, electronic, and transport properties at the bR/perovskite/ETL interface. |
Wednesday, March 6, 2019 12:51PM - 1:03PM |
L47.00009: The Influence of Imperfect Band-edges on the Maximum Efficiency of a Solar Cell Joeson Wong, Stefan Omelchenko, Harry Atwater The theoretical maximum efficiency of a solar cell is given by the Shockley-Queisser Limit, which assumes a step-function absorbance near the band-edge. However, real materials always have an imperfect band-edge, which is usually characterized by an Urbach tail. In this work, we utilize optoelectronic reciprocity relations to develop a modified detailed balance limit of solar cells with imperfect band-edges. We find that for band-edges that are not sharper than the thermal energy, an effective renormalized band-gap is given by the quasi-Fermi level splitting within the solar cell. This renormalized bandgap creates a Stokes shift between the onset of absorption and the photoluminescence peak position, which drastically lowers the maximum achievable efficiency. The band-edge density of states therefore has important implications for the performance of photovoltaic devices. |
Wednesday, March 6, 2019 1:03PM - 1:15PM |
L47.00010: Heterocyclic halides as passivating layer improves photovoltaic properties and intrinsic stability in perovskite solar cells Manuel Salado, Alexander D. Jodlowski, Cristina Roldan-Carmona, Gustavo de Miguel, Samrana Kazim, Mohammad Khaja Nazeeruddin, shahzada Ahmad Perovskites solar cells have irrupted in the photovoltaic field with no precedent. Rising from ~4% to 23.2% the power conversion efficiencies (PCE), however long term stability together with the lack of a fully understanding of intrinsic processes are still issues which need to be undertaken. To improve the intriguing challenges, compositional engineering of perovskites as well as molecular engineering of hole transport materials (HTMs) were adopted. Furthermore, an optimized interface between the different layers of the perovskite device is paramount to improve the problems aforementioned. In this regard, an optimized surface passivation layer is seen as an ideal approach to protect the surface from extrinsic factors, without altering the electro-optical properties. |
Wednesday, March 6, 2019 1:15PM - 1:27PM |
L47.00011: An ab-initio study of water interactions in the hybrid perovskite MAPbI3 Arvin Kakekhani, Andrew Rappe Hybrid (organic-inorganic) perovskites have recently received great attention as candidates for commercially viable and efficient conversion of solar energy. Nevertheless, the performance and stability of these materials gets affected by water and moisture in the environment. Here, using density functional theory (DFT) simulations, and taking MAPbI3 as our case study, we investigate the nature of water interactions in hybrid perovskite MAPbI3. Changing water concentration over 2 orders of magnitude, we study the process of water infiltration and the surface and bulk chemistry that follows and leads to first reversible, and then irreversible changes to the material’s structure. We discuss, based on electronic-structure analyses, how water changes the optical properties of the material in different concentrations. Such understanding of the nature of water--hybrid-perovskite interactions, can then be used to design better and more stable solar cells. |
Wednesday, March 6, 2019 1:27PM - 1:39PM |
L47.00012: Synthesis and optoelectronic properties of Perovskite nanowire Atikur Rahman, Gokul M. A. We have developed a simple solution based synthesis method of CsPbI3 nanowire. This method produces high yield nanowire with controllable length and diameter. We studied in details the effect of various growth conditions, such as temperature and time on the morphology of these nanowires. Single nanowire devices were made to investigate their individual property. To understand different mechanisms that play a major role in determining the performance and stability of these nanowire devices, we studied optoelectronic and noise characteristics under various conditions. These nanowires are structurally stable under ambient condition and show stable photoresponse. We will discuss in details the possible growth mechanism and the observed optoelectronic properties of these nanowires. |
Wednesday, March 6, 2019 1:39PM - 1:51PM |
L47.00013: A density functional theory study (GGA+U) of the electronic and optical properties of Sn doped acanthite Cu2S Sajib Barman, Muhammad Nurul Huda Cu2S is earth abundant, non-toxic and an important semiconductor with many applications. Previously it sought wide attention to scientific community as a promising photovoltaic material since Cu2S based thin film solar cells demonstrated nearly 10% conversion efficiency. Despite excessive Cu vacancy formation tendency, studies on Cu2S based thin film solar cells didn’t lose its importance in decades. Our recently published theoretical study (J. Phys.: Condens. Matter 30 165701) on the acanthite phase of Cu2S showed that Cu vacancy formation tendency can be reduced with Ag alloying. Hence, alloying with other materials needs to be studied systematically, as well. Here, we report a systematic first principle study on Sn doped acanthite Cu2S. We have showed that Sn doping in this structure is even thermodynamically more favorable. Even though excessive Sn doping makes the material metallic, the Cu vacancy formation tendency decreases with high doping concentration. With suitable low doping the material undergoes electronic intraband transition which extends the optical absorption to the infrared region. In addition, detail electronic structures and optical properties will be presented for pure and Sn doped cases. |
Wednesday, March 6, 2019 1:51PM - 2:03PM |
L47.00014: Screening of Metallic Single-Replacements for Lead-free Perovskites with Intrinsic Photovoltaic Functionalities Clark Zhang, Xuan Luo Methylammonium lead triiodide perovskites, CH3NH3PbI3 (MAPbI3), are solution-processable materials with photovoltaic properties capable of surpassing those of silicon solar cells. However, concerns over lead toxicity and lack of exploration into transition metal perovskites drove this ab initio Density Functional Theory screening for environmentally friendly perovskite materials by incorporating transition and post-transition metals at the B-site of MAPbI3. This revealed fourteen replacements to be suitable: their band structures are highly dispersive while band gaps of such materials fall within ideal ranges for single-junction and tandem cells. Transition metal monoreplacements are shown to be viable perovskites after reducing the size of the halide, corroborating that tunability of the band gap is observed in halide replacement at the X-site. Strong peaks in the imaginary output of the dielectric function below 3.5 eV indicate high sunlight absorption efficiency for select materials. Excellent carrier mobility is expected of studied materials as their effective mass is low. This work helps gain further insight into the viability of plentiful transition metals for lower toxicity and higher absorption divalent perovskites. |
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