Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session R38: Photovoltaics: Thin Film and NanostructuredFocus Prize/Award
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Sponsoring Units: GERA Chair: Marton Voros, Argonne Natl. Lab Room: 385 |
Thursday, March 16, 2017 8:00AM - 8:12AM |
R38.00001: Development of New Solar Energy Conversion Materials Based on sp Hybridization Theory Weichang Hao The electron structure of the semiconductors can determine the absorption characters for solar spectrum, and it also determined the excitation, transform and recombination of the electro-hole pairs. According to the band theory of semiconductor, above physical processes always depend on the essential electronic properties such as the band gap, the position of the Fermi level, and the effective mass of the materials. Therefore, the variation of these structure properties may have great effect on the solar energy conversion process. For example, crystal, defects, surface states (include reconstruction and mismatch of the atoms), lattice distortion, and so on can modulate those electronic structure. During the recent years of researching, we gradually found that the materials with \textit{sp} hybridization may develop appropriate electronic structure which is benefit to obtain high-efficiency materials with enhanced light absorption and mobility of the electrons and holes. The main idea is that the sp hybridization orbital is spatially anisotropic and by choosing the applicable elements will form the dispersive band in the CBM and VBM. we can obtain lower effective mass and higher mobility of the electrons and holes, and it is hopeful to find some high-performance solar energy conversion materials via this strategy. . [Preview Abstract] |
Thursday, March 16, 2017 8:12AM - 8:24AM |
R38.00002: Analytical solution for Shockley-Queisser model: Fundamental relations for conversion efficiency Andrei Sergeev, Kimberly Sablon We present analytical solution for photovoltaic conversion efficiency in general Shockley-Queisser model, which assumes thermal and chemical equilibrium between photoelectrons and emitted photons. In this model photoelectrons and phonons are described by the same chemical potential, which provides the useful energy per electron. Our results show that at the electric current which delivers maximal conversion efficiency the emission energy per absorbed photon exactly equals kT. We compare the obtained results with thermodynamic limitations and discuss some paradoxes related to thermodynamics of photovoltaic conversion. [Preview Abstract] |
Thursday, March 16, 2017 8:24AM - 8:36AM |
R38.00003: Finite temperature properties of nanoparticle solids: ab initio simulations Arin Greenwood, Marton Voros, Federico Giberti, Giulia Galli Semiconducting nanoparticle (NP) solids are promising materials for optoelectronic devices such as solar cells. However, there is still much debate regarding the transport regime governing the charge carriers due to the disorder of NP films, and there is a lack of computational studies predicting electron mobilities and transport rates at the ab initio level. Using Ab Initio Molecular Dynamics [1] simulations and Density Functional Theory calculations, we built realistic finite-temperature models of bare and halide-capped [2] lead chalcogenide nanoparticle solids and used these models to extract relevant electronic structure and optical properties to gain insight about charge transport in these systems. Computed properties include band gaps, polarizabilities and dielectric constants, as a function of capping and NP solid morphologies. [1] www.qboxcode.org [2] M. Voros, N. Brawand and G. Galli, to be published in Chemistry of Materials [Preview Abstract] |
Thursday, March 16, 2017 8:36AM - 8:48AM |
R38.00004: Hydrogen treatment as a detergent of electronic trap states in lead chalcogenide nanoparticles Marton Voros, Nicholas Brawand, Giulia Galli Lead chalcogenide (PbX) nanoparticles are promising materials for solar energy conversion. However, the presence of trap states in their electronic gap limits their usability, and developing a universal strategy to remove trap states is a persistent challenge. Using calculations based on density functional theory, we show that hydrogen acts as an amphoteric impurity on PbX nanoparticle surfaces; hydrogen atoms may passivate defects arising from ligand imbalance or off-stoichiometric surface terminations, irrespective of whether they originate from cation or anion excess.[1] In addition, we show, using constrained density functional theory calculations, that hydrogen treatment of defective nanoparticles is also beneficial for charge transport in films. We also find that hydrogen adsorption on stoichiometric nanoparticles leads to electronic doping, preferentially n-type. Our findings suggest that post-synthesis hydrogen treatment of lead chalcogenide nanoparticle films is a viable approach to reduce electronic trap states or to dope well-passivated films. [1] M. Voros, N. Brawand, G. Galli, to be published in Chemistry of Materials. [Preview Abstract] |
Thursday, March 16, 2017 8:48AM - 9:00AM |
R38.00005: Excitation energy dependence of the photovoltaic behavior of InAs/GaAsSb quantum dot solar cells Alison Roeth, Yang Cheng, Anthony Meleco, Vincent Whiteside, Mukul Debnath, Michael Santos, Ian Sellers Intermediate band solar cells (IBSC) have been suggested as a potential route to achieve energy conversion efficiencies higher than that of single gap solar cells by harnessing lower energy light usually lost to transmission. Quantum dots have been proposed as a candidate system for the IB due to their localized nature. Here, InAs quantum dots inserted into the GaAsSb intrinsic region of a solar cell are investigated as a candidate system for IBSCs. The photovoltaic properties of this system will be presented under various conditions of optical excitation: both below (directly in the QDs) and above (in the matrix) the GaAsSb band gap to probe the physical properties of this system. The dependence of open-circuit voltage and short-circuit current as a function of temperature and power will be presented. By varying temperature and power, the effects of carrier confinement, escape, and transport, as well as intrinsic defects and the formation of a well localized intermediate band can all be evaluated. [Preview Abstract] |
Thursday, March 16, 2017 9:00AM - 9:12AM |
R38.00006: Comparative study of polymer and liquid electrolytes in quantum dot sensitized solar cells Uma Poudyal, Wenyong Wang We present the study of CdS/CdSe quantum dot sensitized solar cells (QDSSCs) in which Zn$_{\mathrm{2}}$SnO$_{\mathrm{4\thinspace }}$nanowires on the conductive glass are used as photoanode. The CdS/CdSe quantum dots (QDs) are deposited in the Zn2SnO4 photoanode by the Successive Ionic Layer Adsorption and Reaction (SILAR) method. CdS is first deposited on the nanowires after which it is further coated with 5 cycles of CdSe QDs. Finally, ZnS is coated on the QDs as a passivation layer. The QD sensitized photoanode are then used to assemble a solar device with the polymer and liquid electrolytes. The Incident Photon to Current Efficiency (IPCE) spectra are obtained for the CdS/CdSe coated nanowires. Further, a stability test of these devices is performed, using the polymer and liquid electrolytes, which provides insight to determine the better working electrolyte in the CdS/CdSe QDSSCs. [Preview Abstract] |
Thursday, March 16, 2017 9:12AM - 9:24AM |
R38.00007: Nanoscopic characterizations of photo-generated carriers in P3HT/Si hybrid nanostructures Eunah Kim, Yunae Cho, Ahrum Sohn, Heewon Hwang, Y. U. Lee, Kyungkon Kim, Hyeong-Ho Park, Joondong Kim, J. W. Wu, Dong-Wook Kim The extremely short exciton diffusion lengths in organic semiconductors limit the photovoltaic performance of the organic solar cells. Therefore, organic/Si hybrid (OSH) nanostructured devices have been proposed. The Si nanostructures can provide pathways for efficient carrier transportation because of the high mobility of Si and the large junction area in such devices. In this work, we fabricated Si nanopillar (NP) arrays coated with poly(3-hexylthiophene-2,5-diyl) (P3HT) organic semiconductor layers. Optical reflection spectra and simulated optical generation rate distribution showed that Mie-like geometrical resonance significantly concentrated incident light in the NPs. We studied the surface photovoltage (SPV) characteristics of the OSH nanostructures using the Kevin probe force microscopy technique to investigate the spatial distributions of photo-generated carriers. Under red light, SPV value is much larger at the NP top surface than that of planar sample. Such SPV behavior directly revealed that the concentrated light produced numerous charge carriers in the NPs. This suggested that the optical resonance in OSH nanostructures benefits not only broad-band light trapping but also efficient carrier collection. [Preview Abstract] |
Thursday, March 16, 2017 9:24AM - 9:36AM |
R38.00008: Plasmonic Enhancement of Organic Photovoltaic Devices Huy Nguyen, Rachel Owen, Martin Fernandez, Brad Johnson, Janelle Leger With the increasing demand for clean and renewable energy, organic photovoltaics (OPVs) provide a sustainable alternative to silicon based solar cells. While OPVs have the potential of being thinner and more affordable than their precursors, improving conversion efficiency of these devices has been challenging. One method that has been proposed for increasing device performance is the use of plasmonic waveguides as an electrical back contact to OPVs. Photons not absorbed by the active layer can excite charge density oscillations known as surface plasmon polaritons (SPPs) and provide an additional mechanism for energy conversion. However, overcoming propagation losses that occur at the metal-dielectric interface is a crucial step before significant improvements in OPV performance can be realized. Recently we have demonstrated a waveguide structure with a core dielectric layer of high refractive index capable of supporting guided wave plasmon polaritons modes (GW-PPMs). Unlike traditional SPPs, GW-PPMs have electric fields concentrated in the bulk dielectric leading to the potential for increased propagation lengths. Here we present our preliminary steps to GW-PPM waveguide and OPV integration with the goal of enhanced conversion efficiency. [Preview Abstract] |
Thursday, March 16, 2017 9:36AM - 9:48AM |
R38.00009: Effect of Cobalt Doping on ZnO/CuO Heterojunction Solar Cell Amrit Kaphle, Ram Tiwari, Parameswar Hari In this study, we report optical and electrical characterization of nanostructured ZnO/CuO heterojunctions with cobalt doping. CuO p-layer was deposited by DC sputtering and ZnO nanorods (n-layer) were fabricated on fluorine doped tin oxide (FTO) substrate by a chemical bath deposition technique. We investigated the structural, optical, and electrical properties of the ZnO/CuO heterojunction. Optical properties were investigated using UV-VIS spectroscopy. Absorption measurements show a decrease in electronic band gap with increase in cobalt concentration. Current- Voltage (I-V) measurements show that as the cobalt percentage increased from 0-20{\%}, the power conversion efficiency of the CuO/ZnO solar cell increased from 1.70{\%} to 2.93{\%}. This increase in conversion efficiency also resulted in changes in fill factor (62.09{\%} - 69.93{\%}), current density (3.62 mA/cm$^{\mathrm{2}}$ -- 5.07 mA/cm$^{\mathrm{2}})$, and open circuit voltage (0.56 V - 0.61 V). Our external quantum efficiency (EQE) measurements show an increase in EQE from 5.11{\%} to 9.34{\%} in the visible range with doping. We will discuss the implications of these results based on cobalt incorporation in ZnO nanostructure. [Preview Abstract] |
Thursday, March 16, 2017 9:48AM - 10:24AM |
R38.00010: Functional imaging of photovoltaic materials Invited Speaker: Marina Leite For the past two decades, extensive efforts have been made to increase the short-circuit current (Jsc) of non-epitaxial solar cells to achieve higher efficiency devices. Yet, improvements in the overall device performance are still limited by the open-circuit voltage (Voc). We address this critical limiting factor of all promising materials for photovoltaics by realizing a novel nanoscale imaging platform with unprecedented spatial resolution (\textless 100 nm), based on a variant of Kelvin-probe force microscopy. We mapped the local Voc of a variety of inorganic materials, and measured local changes \textgreater 150 mV in CIGS, not resolved by conventional electrical measurements. To identify the origin of the instability frequently observed in perovskite solar cells, we leveraged our recently developed method to scan one frame in 16 seconds to spatially and temporally resolve their photo-voltage. Surprisingly, we observed local and reversible changes in the Voc of the devices upon post-illumination treatments. Our innovative functional imaging is non destructive and can be applied to other optoelectronic devices, such as LEDs and photodetectors. [Preview Abstract] |
Thursday, March 16, 2017 10:24AM - 10:36AM |
R38.00011: First principle investigation of the stability of silver alloyed acanthite Cu$_{\mathrm{2}}$S. Sajib Barman, Muhammad Huda As a potential solar absorber material, Cu$_{\mathrm{2}}$S has proved its importance in the field of renewable energy. However, almost all the known minerals of Cu$_{\mathrm{2}}$S suffer from spontaneous Cu vacancy formation in the structure. The Cu vacancy formation causes the structure to possess very high p-type doping that leads the material to behave as a degenerate semiconductor. This instability toward Cu vacancy formation is a vital obstacle for this material in this regard, which needs to be addressed properly. A relatively new predicted phase of Cu$_{\mathrm{2}}$S which has an acanthite-like structure is found more preferable than the well-known low chalcocite Cu$_{\mathrm{2}}$S. However, the Cu-vacancy formation tendency does not reduce. Alloying silver with this structure shows that Cu vacancy formation tendency can be reduced without altering its electronic property significantly. Here, we present a systematic approach within the density functional theory framework to study the stability of silver alloyed acanthite Cu$_{\mathrm{2}}$S. [Preview Abstract] |
Thursday, March 16, 2017 10:36AM - 10:48AM |
R38.00012: II-I$_2$-IV-VI$_4$ (II = Sr,Ba; I = Cu,Ag; IV = Ge,Sn; VI = S,Se): Earth-Abundant Chalcogenides for Thin Film Photovoltaics Tong Zhu, William P. Huhn, Donghyeop Shin, David B. Mitzi, Volker Blum, Bayrammurad Saparov Chalcogenides such as CdTe, CIGSSe, and CZTSSe are successful for thin film photovoltaics (PV) but contain elements that are rare, toxic, or prone to the formation of detrimental antisite disorder. Recently, the BaCu$_2$SnS$_{4-x}$Se$_x$ system has been shown to offer a prospective path to circumvent these problems.[1] While early prototypes show efficiencies of a few percent, many avenues remain to optimize the materials, including the underlying chemical composition. In this work, we explore 16 compounds II-I$_2$-IV-VI$_4$ to help identify new candidate materials for PV, with predictions based on both known experimental and computationally derived structures that belong to five different space groups. We employ hybrid density functional theory (HSE06) to explore the band gap tunability by substituting different elements, and other characteristics such as the effective mass and the absorption coefficient. Compounds containing Cu (rather than Ag) are found to have direct or nearly direct band gaps. Depending on the compound, replacing S with Se leads to a decrease of the predicted band gaps by 0.2-0.8 eV and to somewhat decreasing hole effective masses. [1] Shin {\it et al.}, Chem. Mater. 28, 4771 (2016). [Preview Abstract] |
Thursday, March 16, 2017 10:48AM - 11:00AM |
R38.00013: Properties of Electrodeposited Metal Sulfide Films for photovoltaic applications Pawanjit Kaur, Maggie Paulose, Oomman Varghese Binary, ternary and quaternary metal sulfide films are of considerable interest as components in solar cells. Some of these materials are earth abundant and have the potential to yield low cost devices. Among these materials, Cu2ZnSnS4 (CZTS) and its variant Cu2ZnSnSxSe1-x (CZTSSe) have shown promising properties as light absorbers. Efficiencies exceeding 12{\%} were reported in devices employing CZTSSe as light absorber. Nevertheless, fabrication of these materials without secondary phases such as ZnS is a major problem. In order to minimize the challenges associated with such quaternary materials, we reduced the number of elements and fabricated ternary metal sulfides using electrodeposition, which is a scalable technique. We will discuss the promising properties of these materials as light absorbers in solar cells. [Preview Abstract] |
Thursday, March 16, 2017 11:00AM - 11:12AM |
R38.00014: The Effect of PEDOT:PSS Back Contact on CdTe/polymer Solar Cells Prof Weining Wang, Brooke Myers, Tyler Lucas, Brandon Barnes, Naba Paudel, Yanfa Yan In our previous studies, we reported the potential of conducting polymer being used as the back contact of CdTe/CdS solar cells, with the efficiency of the CdTe solar cell with the poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) back contact approaching those with traditional Cu/Au back contact. In this work, we report our studies on the effect of conductivity and work function of the polymer on the characteristics of CdTe/polymer solar cells. A series of conducting polymer with different conductivity and work function were used as back contact for CdTe solar cells. We have found that the solar cells with higher polymer conductivity yields higher fill factor and higher short-circuit current, and the solar cells with higher polymer work function yields higher open-circuit voltage. We also studied the effect of polymer work function on the barrier height of the CdTe/polymer junction. Those results help us gain a better understanding on the energy level alignment at CdTe/polymer junction, and provide insight on developing more efficient CdTe/polymer solar cells. [Preview Abstract] |
Thursday, March 16, 2017 11:12AM - 11:24AM |
R38.00015: Transmissive concentrator multijunction solar cells with 47{\%} in-band efficiency for a hybrid photovoltaic-solar thermal system Qi Xu, Yaping Ji, Dimitri Krut, Jim Ermer, matthew escarra Transmissive concentrator multijunction (TCMJ) solar cells with over 47{\%} in-band power conversion efficiency (PCE) have been demonstrated. The illuminated I-V test under concentrated 500-sun solar spectra have shown that the PCE of the TCMJ solar cells for in-band light (photon energy above the cell's lowest bandgap) can reach up to 47.6{\%} (29.5{\%} for the full solar spectrum). Temperature coefficients of several parameters (open circuit voltage, short circuit current, fill factor) have been derived under 1 sun and 500 suns, showing linear variations versus temperature change. Optical measurements indicate that the cells show 76.5{\%} solar-weighted optical transmission for the out-of-band light (photon energy below the cell's lowest bandgap). This TCMJ solar cell exhibits promising spectrum splitting capability, which has potential for use in hybrid photovoltaic-solar thermal energy conversion systems. [Preview Abstract] |
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