Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session P38: Perovskite Solar Cell |
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Sponsoring Units: GERA Chair: Maria Chan, ANL Room: 385 |
Wednesday, March 15, 2017 2:30PM - 2:42PM |
P38.00001: Phonon properties and slow organic-to-inorganic sub-lattice thermalization in hybrid perovskites Maria Chan, Angela Chang, Yi Xia, Sridhar Sadasivam, Peijun Guo, Alper Kinaci, Hao-Wu Lin, Pierre Darancet, Richard Schaller Organic-inorganic hybrid perovskite halide compounds have been investigated extensively for photovoltaics (PVs) and related applications. The thermal transport properties of hybrid perovskites, including phonon-carrier and phonon-phonon interactions, are of significance for their PV and solar thermoelectric applications. The interlocking organic and inorganic sublattices can be thought of as an extreme form of nanostructuring. A result of this nanostructuring is the large gap in phonon frequencies between the organic and inorganic sublattices, which is expected to create bottlenecks in phonon equilibration. In this work, we use a combination of ultrafast spectroscopy including photoluminescence and transient absorption, as well as first principles density functional theory (DFT), ab initio molecular dynamics calculations, phonon lifetimes derived from DFT force constants, and non-equilibrium phonon dynamics accounting for phonon lifetimes, to determine the phonon and charge interaction processes. We find evidence that thermalization of carriers occur at an atypically slow ~50-100 ps time scale owing to the complex interplay between electronic and phonon excitations (A. Y. Chang et al, Advanced Energy Materials 2016, DOI: 10.1002/aenm.201600422). [Preview Abstract] |
Wednesday, March 15, 2017 2:42PM - 2:54PM |
P38.00002: Coexistence of Two Electronic Nano-Phases on a CH$_{3}$NH$_{3}$PbI$_{3-x}$Cl$_{x}$ Surface Observed in STM Measurements Andrew J Yost, Artem Pimachev, Chun-Chih Ho, Seth B. Darling, Leeyih Wang, Wei-Fang Su, Yuri Dahnovsky, TeYu Chien Scanning tunneling microscopy is utilized to investigate the local density of states of a CH$_{3}$NH$_{3}$PbI$_{3-x}$Clx perovskite in cross-sectional geometry. Two electronic phases, 10$-$20 nm in size, with different electronic properties inside the CH$_{3}$NH$_{3}$PbI$_{3-x}$Cl$_{x}$ perovskite layer are observed by the d$I$/d$V$ mapping and point spectra. In addition, the distinct electronic phases are found to have preferential orientations close to the normal direction of the film surface. Density functional theory calculations indicate that the observed electronic phases are associated with local deviation of I/Cl ratio, rather than different orientations of the electric dipole moments in the ferroelectric phases. By comparing the calculated results with experimental data we conclude that phase A (lower contrast in d$I$/d$V$ mapping at $-$2.0 V bias) contains a lower I/Cl ratio than that in phase B (higher contrast in d$I$/d$V)$.$^{1}$ [1] \textit{ACS Appl. Mater. Interfaces},~\textbf{2016},~8~(42), pp 29110--29116 [Preview Abstract] |
Wednesday, March 15, 2017 2:54PM - 3:06PM |
P38.00003: Effect of disorder on transport properties in a tight-binding model for organo-metal halide perovskites Sahel Ashhab, O. Voznyy, S. Hoogland, E. H. Sargent, M. E. Madjet The organo-metal halide perovskite materials have recently emerged as remarkable materials for photovoltaic applications. Their strengths include good electric transport properties in spite of the disorder inherent in them. Motivated by this observation, we analyze the effects of disorder on the energy eigenstates of a tight-binding model of these materials. In particular, we analyze the spatial extension of the energy eigenstates, which is quantified by the inverse participation ratio. This parameter exhibits a gradual change towards localization as the on-site energy disorder strength is increased. However, we argue that the disorder in the organo-metal halide perovskites corresponds to a point in the regime of highly delocalized states. Our results also suggest that the form of the electronic states is not favorable for halide mixing. [Preview Abstract] |
Wednesday, March 15, 2017 3:06PM - 3:18PM |
P38.00004: CH$_{\mathrm{3}}$NH$_{\mathrm{3}}$PbI$_{\mathrm{3}}$ and CsPbI$_{\mathrm{3}}$ Supramolecular Clusters in 1D: Do They Evolve with the Same Principle of Cooperative Binding? Arpita Varadwaj, Pradeep R. Varadwaj, Koichi Yamashita Development of novel semiconductor-based photo-catalytic and --voltaic systems is a major area of research in nanoscience and technologies, and engineering. The process can be either direct or indirect in converting the light energy into electricity. Some of the photovoltaics include the organic, dye-sensitized, and halide perovskite solar cells, among others. Methylammonium lead iodide (CH$_{\mathrm{3}}$NH$_{\mathrm{3}}$PbI$_{\mathrm{3}})$ inorganic-organic hybrid perovskite is one among the many highly valued semiconductors reported till date, comparable with the inorganic cesium lead iodide (CsPbI$_{\mathrm{3}})$ perovskite. These are competitive candidates in the solar energy race. Nevertheless, this study was concentrated on the fundamental understanding of the rational designs of the CH$_{\mathrm{3}}$NH$_{\mathrm{3}}$PbI$_{\mathrm{3}}$ and CsPbI$_{\mathrm{3}}$ supramolecular materials using first-principles calculations, emerged though the self-assembly of the respective building blocks. It therefore addresses the question whether the (CH$_{\mathrm{3}}$NH$_{\mathrm{3}}$PbI$_{\mathrm{3}})_{\mathrm{n}}$ and (CsPbI$_{\mathrm{3}})_{\mathrm{n}}$ (n$=$1--10) supramolecular clusters are the consequences of additivity, or non-additive cooperative binding? For addressing this question, the supramolecular properties such as the polarizability, the intermolecular charge transfer, and the binding energy, etc., all w.r.t the cluster size n, are exploited. [Preview Abstract] |
Wednesday, March 15, 2017 3:18PM - 3:30PM |
P38.00005: Comparative Study of Phonon Modes and Carrier Mobility in CH$_{3}$NH$_{3}$PbX$_{3}$ (X $=$ Cl, Br, I) Perovskites using Terahertz Time-Domain Spectroscopy Daming Zhao, Hongwei Hu, Teddy Salim, Liang Cheng, Chan La-o-vorakiat, Yeng Ming Lam, Rudolph Marcus, Maria-Elisabeth Michel-Beyerle, Elbert Chia Since organometallic halide perovskites are not only light absorbers but also hole-transporting materials in photovoltaic applications, high carrier mobility is therefore desired. In polar semiconductors (e.g. CH$_{3}$NH$_{3}$PbX$_{3})$, the charge carrier mobility is limited by electron-optical phonon scattering, whose upper limit depends sensitively on the lowest-frequency phonon modes. Using THz time-domain spectroscopy, we examine the temperature evolution of these phonon modes, and then calculate their carrier mobilities. This method allows us to estimate the carrier mobilities without the need to create photogenerated free carriers, and can be applied to other dipole semiconductor systems. [Preview Abstract] |
Wednesday, March 15, 2017 3:30PM - 3:42PM |
P38.00006: Efficient organic-inorganic hybrid perovskites and doped metal oxide heterojunction solar cells. Xiaojuan Fan Organic-Inorganic hybrid perovskite CH3NH3PbI3 has recently attracted much attention for its high efficient solar energy conversion. This semiconducting pigment with a direct bandgap of 1.55 eV has made it an interesting optical and electronic material over the whole visible solar emission spectrum. The role of hole conducting has been found in this semiconductor that allows perovskite solar cell (PSC) to be formed by CH3NH3PbI3/TiO2 heterojunctions that use TiO2 as scaffold, and carbon as a back contact. We will report a double layer metal doped TiO2/Al2O3 mesoporous scaffold covered by the p-type semiconducting pigment to form a high efficient PSC through solution method. TiO2 and Al2O3 are both large band gap semiconductors that affect conducting and recombination rate in solar cells. One improvement work is doping other metal elements in TiO2 to raise the mobility while extend the recombination time. It has suggested that optimal amounts of doped metals such as Cu, Co, Mn can suppress the reduction of Ti4$+$ resulting better transportation. TiO2 thin films doped with metals are subjected to the EPR analysis and the results will be correlated with measurements of electronic-optical properties. [Preview Abstract] |
Wednesday, March 15, 2017 3:42PM - 3:54PM |
P38.00007: Electro-hydrodynamic spray synthesis and low temperature spectroscopic characterization of Perovskite thin films Som Sarang, Hidetaka Ishihara, Vincent Tung, Sayantani Ghosh Utilizing a Marangoni flow inspired electrospraying technique, we synthesize hybrid perovskite (PVSK) thin films with broad absorption spectrum and high crystallinity. The precursor solvents are electrosprayed onto an indium tin oxide (ITO) substrate, resulting in a gradient force developing between the droplet surface and the bulk due to the varying vapor pressure in the bi-solvent system. This gradient force helps the droplets propagate and merge with surrounding ones, forming a uniform thin film with excellent morphological and topological characteristics, as evident from the average power conversion efficiency (PCE) of 16{\%}. In parallel, we use low temperature static and dynamic photoluminescence spectroscopy to probe the grain boundaries and defects in the synthesized PVSK thin films. At 120 K, the emergence of the low temperature orthorhombic phase is accompanied by reduction in lifetimes by an order of magnitude, a result attributed to charge transfer between the orthorhombic and tetragonal domains, as well as due to a crossover from free charge carrier to excitonic recombination. Our fabrication technique and optical studies help in advancement of PVSK based technology by providing unique insights into the fundamental physics of these novel materials. [Preview Abstract] |
Wednesday, March 15, 2017 3:54PM - 4:06PM |
P38.00008: Light-modulated scanning tunneling microscopy studied on photoinduced carrier generations at PbI$_{2}$/perovskite interface of perovskite solar cells Ya-Ping Chiu, Min-Chuan Shih, Shao-Sian Li, Cheng-Hua Hsieh, Ying-Chiao Wang, Hung-Duen Yang, Chia-Seng Chang, Chun-Wei Chen Perovskite solar devices based on CH$_{3}$NH$_{3}$PbX$_{3}$ (X = Cl, Br, I) have recently shown tremendous efficiency enhancements up to 20\% in photovoltaic applications. The presence of PbI2 in perovskite films has been found to affect the charge carrier transport behaviors and device performance of perovskite solar cells. In this work, we employed the unique ability of light-modulated scanning tunneling microscopy (LM-STM) technique to dircetly reveal the correlation of the nanoscaled compositional distributions and photo-induced interfacial electronic structures at the PbI2/perovskite interface of perovskite grains under light illumination. The result reveals the important role of the optimum PbI$_{2}$ passivation layers (a thickness less than 20 nm) on the charge separation and recombination at perovskite crystal grains. The unique LM-STM technique demonstartes great potential for application in the future exploring photovoltaic systems. [Preview Abstract] |
Wednesday, March 15, 2017 4:06PM - 4:18PM |
P38.00009: Role of Ionic Functional Groups on Ion Transport at Perovskite Interfaces yao liu, Lawrence Renna, Hilary Thompson, Zachariah Page, Todd Emrick, Michael Barnes, Monojit Bag, D. Venkataraman, Thomas Russell Hybrid organic/inorganic perovskite solar cells have invigorated the photovoltaic community with their remarkable properties. However, many perovskite solar cells show an undesirable current-voltage ($I-V)$ hysteresis in their forward and reverse voltage scans, to the detriment of device characterization and performance. This hysteresis is likely due to slow ion migration in the bulk of the perovskite active layer. We show the interfacial chemistry between the perovskite and charge transport layer plays a critical role in the ion transport and subsequent $I-V$ hysteresis in perovskite based devices. Three phenylene vinylene polymers containing cationic, zwitterionic, and anionic pendent groups were utilized to fabricate charge transport layers with diverse interfacial ionic functionalities. The interfacial-adsorbing boundary induced by the polymer zwitterion at the interface traps mobile ions, responsible for the $I-V$ hysteresis in these perovskite-based devices. Further, we exploit the ion adsorbing nature of the interface to fabricate perovskite-based memristors. Here, we examine a new chemical mechanism fundamental to $I-V$ hysteresis in perovskite-based devices and introduces a novel paradigm of interfacial ion adsorption to induce memristive behavior. [Preview Abstract] |
Wednesday, March 15, 2017 4:18PM - 4:30PM |
P38.00010: Optimization of Hybrid Perovskite Thin Films as Luminescent Solar Concentrators Benaz Mendewala, Katerina Nikolaidau, Som Sarang, Christine Hoffman, Vincent Tung, Boaz Ilan, Sayantani Ghosh Thin film hybrid perovskites have emerged as exciting new materials for photovoltaic applications owing to their broad absorption, large Stokes shift and high quantum yield. These traits also make them excellent candidates for luminescent solar concentrators (LSCs). Following synthesis and optical and electronic characterization of 16 perovskite thin film composites with varying lead halide precursors and film thickness, we report high optical efficiencies in the range of 21- 35{\%}, making these devices competitive with other top-performing LSCs. We input experimental results including surface morphology, self-absorption and quantum yield into three-dimensional Monte Carlo simulations. Comparing and contrasting the simulated outcomes with device performance leads to the conclusion that quantum yield is the most critical parameter for optimizing LSC efficiency. Additionally, we demonstrate that while perovskite based solar cells degrade rapidly, our devices remain functional for up to two months under ambient conditions. [Preview Abstract] |
Wednesday, March 15, 2017 4:30PM - 4:42PM |
P38.00011: Electronic Structure and Stability of the CH$_{\mathbf{3}}$\textbf{NH}$_{\mathbf{3}}$\textbf{PbBr}$_{\mathbf{3}}$\textbf{ (001) Surface} Tula R. Paudel, Xin Huang, Peter Dowben, Shuai Dong, Evgeny Tsymbal The energetics and the electronic structure of methylammonium lead bromine (CH$_{3}$NH$_{3}$PbBr$_{3})$ perovskite (001) surfaces are studied based on density functional theory. By examining the surface grand potential, we predict that the CH$_{3}$NH$_{3}$Br-terminated (001) surface is energetically more favorable than the PbBr$_{2}$-terminated (001) surface, under thermodynamic equilibrium conditions of bulk CH$_{3}$NH$_{3}$PbBr$_{3}$. The electronic structure of each of these two different surface terminations retains some of the characteristics of the bulk, while new surface states are found near band edges which may affect the photovoltaic performance in the solar cells based on CH$_{3}$NH$_{3}$PbBr$_{3}$. The calculated electron affinity of CH$_{3}$NH$_{3}$PbBr$_{3}$ reveals a sizable difference for the two surface terminations, indicating a possibility of tuning the band offset between the halide perovskite and adjacent electrode with proper interface engineering. [Preview Abstract] |
Wednesday, March 15, 2017 4:42PM - 4:54PM |
P38.00012: Long-Term Stability of Photovoltaic Hybrid Perovskites achieved by Graphene Passivation via a Water- and Polymer-Free Graphene Transfer Method W.-S. Tseng, M.-H. Jao, C.-C. Hsu, C.-I. Wu, N.-C. Yeh Organic-inorganic hybrid perovskites such as CH$_{3}$NH$_{3}$PbX$_{3}$ (X $=$ I, Br) have been intensively studied in recent years because of their rapidly improving photovoltaic power conversion efficiency. However, severe instability of these materials in ambient environment has been a primary challenge for practical applications. To address this issue, we employ high-quality PECVD-grown graphene to passivate the hybrid perovskites. In contrast to existing processes for transferring graphene from the growth substrates to other surfaces that involve either polymer or water, which are incompatible with photovoltaic applications of these water-sensitive hybrid perovskites, we report here a new water- and polymer-free graphene transferring method. Studies of the Raman, x-ray and ultraviolet photoemission spectroscopy (XPS and UPS) demonstrated excellent quality of monolayer PECVD-grown graphene samples after their transfer onto different substrates with the water- and polymer-free processing method. In particular, graphene was successfully transferred onto the surface of CH$_{3}$NH$_{3}$PbI$_{3}$ thin films with sample quality intact. Moreover, XPS and UPS studies indicated that even after 3 months, the fully graphene-covered perovskite films remained spectroscopically invariant, which was in sharp contrast to the drastic changes, after merely one week, in both the XPS and UPS of a control CH$_{3}$NH$_{3}$PbI$_{3}$ sample without graphene protection. [Preview Abstract] |
Wednesday, March 15, 2017 4:54PM - 5:06PM |
P38.00013: ZnO nanostructures as electron extraction layers for hybrid perovskite thin films Katerina Nikolaidou, Som Sarang, Vincent Tung, Jennifer Lu, Sayantani Ghosh Optimum interaction between light harvesting media and electron transport layers is critical for the efficient operation of photovoltaic devices. In this work, ZnO layers of different morphologies are implemented as electron extraction and transport layers for hybrid perovskite CH$_{\mathrm{3}}$NH$_{\mathrm{3}}$PbI$_{\mathrm{3}}$ thin films. These include nanowires, nanoparticles, and single crystalline film. Charge transfer at the ZnO/perovskite interface is investigated and compared through ultra-fast characterization techniques, including temperature and power dependent spectroscopy, and time-resolved photoluminescence. The nanowires cause an enhancement in perovskite emission, which may be attributed to increased scattering and grain boundary formation. However, the ZnO layers with decreasing surface roughness exhibit better electron extraction, as inferred from photoluminescence quenching, reduction in the number of bound excitons, and reduced exciton lifetime in CH$_{\mathrm{3}}$NH$_{\mathrm{3}}$PbI$_{\mathrm{3}}$ samples. This systematic study is expected to provide an understanding of the fundamental processes occurring at the ZnO-CH$_{\mathrm{3}}$NH$_{\mathrm{3}}$PbI$_{\mathrm{3}}$ interface and ultimately, provide guidelines for the ideal configuration of ZnO-based hybrid Perovskite devices. [Preview Abstract] |
Wednesday, March 15, 2017 5:06PM - 5:18PM |
P38.00014: Carrier mobility enhancement of nano-crystalline semiconductor films: Incorporation of redox -relay species into the grain boundary interface L. A. DeSilva, T.M.W.J. Bandara, B.H. Hettiarachchi, G.R.A. Kumara, A.G.U. Perera, R.M.G. Rajapaksa, K. Tennakone Dye-sensitized and perovskite solar cells and other nanostructured heterojunction electronic devices require securing intimate electronic contact between nanostructured surfaces. Generally, the strategy is solution phase coating of a hole -collector over a nano-crystalline high-band gap n-type oxide semiconductor film painted with a thin layer of the light harvesting material. The nano-crystallites of the hole -- collector fills the pores of the painted oxide surface. Most ills of these devices are associated with imperfect contact and high resistance of the hole conducting layer constituted of nano-crystallites. Denaturing of the delicate light harvesting material forbid sintering at elevated temperatures to reduce the grain boundary resistance. It is found that the interfacial and grain boundary resistance can be significantly reduced via incorporation of redox species into the interfaces to form ultra-thin layers. Suitable redox moieties, preferably bonded to the surface, act as electron transfer relays greatly reducing the film resistance offerring a promising method of enhancing the effective hole mobility of nano-crystalline hole-collectors and developing hole conductor paints for application in nanostructured devices. [Preview Abstract] |
Wednesday, March 15, 2017 5:18PM - 5:30PM |
P38.00015: Low-temperature thermal conductivity of the metal-organic perovskite [C(NH$_2$)$_3$][Cu(HCOO)$_3$] Dharmendra Shukla, Narayan Prasai, Joshua L. Cohn, Mercedes M. A. Mazza, Amy M. Scott We report measurements of thermal conductivity on single crystals of the metal-organic hybrid perovskite [C(NH$_2$)$_3$][Cu(HCOO)$_3$] in the temperature range 5K to 300K. In addition to its potential in photovoltaic applications, this compound draws interest for its low-dimensional antiferromagnetism associated with Cu-formate chains (along the crystallographic $c$-axis of the orthorhombic structure).$^a$ We will present thermal conductivity measurements along the three main symmetry directions ([100], [010], and [001]) and discuss its anisotropy. \vskip .1in \noindent $^a$ Hu {\it et al.}, Chem. Eur. J. {\bf 15}, 12050 (2009). [Preview Abstract] |
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