Advancing perovskite solar cell technologies toward their theoretical power conversion efficiency (PCE) requires delicate control over the carrier dynamics throughout the entire device. By controlling the formation of the perovskite layer and careful choices of other materials, we suppressed carrier recombination in the absorber, facilitated carrier injection into the carrier transport layers, and maintained good carrier extraction at the electrodes. When measured via reverse bias scan, cell PCE is typically boosted to 16.6% on average, with the highest efficiency of ~19.3% in a planar geometry without antireflective coating. The fabrication of our perovskite solar cells was conducted in air and from solution at low temperatures, which should simplify manufacturing of large-area perovskite devices that are inexpensive and perform at high levels.

http://science.sciencemag.org/content/sci/345/6196/542.full.pdf

Interface engineering of highly efficient perovskite solar cells

Metamaterials are artificially fabricated materials that allow for the control of light and acoustic waves in a manner that is not possible in nature. This Review covers the recent developments in the study of so-called metasurfaces, which offer the possibility of controlling light with ultrathin, planar optical components. Conventional optical components such as lenses, waveplates and holograms rely on light propagation over distances much larger than the wavelength to shape wavefronts. In this way substantial changes of the amplitude, phase or polarization of light waves are gradually accumulated along the optical path. This Review focuses on recent developments on flat, ultrathin optical components dubbed 'metasurfaces' that produce abrupt changes over the scale of the free-space wavelength in the phase, amplitude and/or polarization of a light beam. Metasurfaces are generally created by assembling arrays of miniature, anisotropic light scatterers (that is, resonators such as optical antennas). The spacing between antennas and their dimensions are much smaller than the wavelength. As a result the metasurfaces, on account of Huygens principle, are able to mould optical wavefronts into arbitrary shapes with subwavelength resolution by introducing spatial variations in the optical response of the light scatterers. Such gradient metasurfaces go beyond the well-established technology of frequency selective surfaces made of periodic structures and are extending to new spectral regions the functionalities of conventional microwave and millimetre-wave transmit-arrays and reflect-arrays. Metasurfaces can also be created by using ultrathin films of materials with large optical losses. By using the controllable abrupt phase shifts associated with reflection or transmission of light waves at the interface between lossy materials, such metasurfaces operate like optically thin cavities that strongly modify the light spectrum. Technology opportunities in various spectral regions and their potential advantages in replacing existing optical components are discussed.

Flat Optics With Designer Metasurfaces

-phenylenevinylene)s L4. Fluorene-Based Conjugated Polymers L4.1. Fluorene-Based Copolymers ContainingElectron-Rich MoietiesM4.2. Fluorene-Based Copolymers ContainingElectron-Deﬁcient MoietiesN4.3. Fluorene-Based Copolymers ContainingPhosphorescent ComplexesQ5. Carbazole-Based Conjugated Polymers R5.1. Poly(2,7-carbazole)-Based Polymers R5.2. Indolo[3,2-

https://ir.nctu.edu.tw:443/bitstream/11536/6508/1/000271856900020.pdf

Synthesis of Conjugated Polymers for Organic Solar Cell Applications

2.2. Materials 929 2.3. Factors Influencing Charge Mobility 931 2.3.1. Molecular Packing 931 2.3.2. Disorder 932 2.3.3. Temperature 933 2.3.4. Electric Field 934 2.3.5. Impurities 934 2.3.6. Pressure 934 2.3.7. Charge-Carrier Density 934 2.3.8. Size/molecular Weight 935 3. The Charge-Transport Parameters 935 3.1. Electronic Coupling 936 3.1.1. The Energy-Splitting-in-Dimer Method 936 3.1.2. The Orthogonality Issue 937 3.1.3. Impact of the Site Energy 937 3.1.4. Electronic Coupling in Oligoacene Derivatives 938

Charge transport in organic semiconductors.

A novel non-fullerene electron acceptor (ITIC) that overcomes some of the shortcomings of fullerene acceptors, for example, weak absorption in the visible spectral region and limited energy-level variability, is designed and synthesized. Fullerene-free polymer solar cells (PSCs) based on the ITIC acceptor are demonstrated to exhibit power conversion effi ciencies of up to 6.8%, a record for fullerene-free PSCs.

An electron acceptor challenging fullerenes for efficient polymer solar cells.

We show that adding ethylenediamine (EDA) to perovskite precursor solution improves the photovoltaic device performance and material stability of high-bromide-content, methylammonium-free, formamidinium cesium lead halide perovskites FA1-xCsxPb(I1-yBry)3 which are currently of interest for perovskite-on-Si tandem solar cells. Using spectroscopy and hyperspectral microscopy, we show that the additive improves film homogeneity and suppresses the phase instability that is ubiquitous in high-Br perovskite formulations, producing films that remain stable for over 100 days in ambient conditions. With the addition of 1 mol% EDA we demonstrate 1.69 eV-gap perovskite single-junction p-i-n devices with a VOC of 1.22 V, and a champion maximum power point tracked power conversion efficiency of 18.8%, comparable to the best reported methylammonium-free perovskites. Using nuclear magnetic resonance (NMR) spectroscopy and X-ray diffraction techniques, we show that EDA reacts with FA in solution, rapidly and quantitatively forming imidazolinium cations. It is the presence of imidazolinium during crystallization which drives the improved perovskite thin-film properties.

/pdf/ethylenediamine-addition-improves-performance-and-suppresses-2d34ixda.pdf

Ethylenediamine Addition Improves Performance and Suppresses Phase Instabilities in Mixed-Halide Perovskites

A new fused-ring compound 1,2,3,4,5,6,7,8-octamethyl-1,5-dihydro-s-indacene (H2L1) has been synthesized from p-xylene. Three transition-metal derivatives [Mn(η5-HL1)(CO)3], [Rh(η5-HL1)(η-C5Me5)]+[SbF6]− and [Cr(η6-H2L1)(CO)3] have been characterised: spectroscopic and crystallographic data for these compounds show the ligand system is strongly electron donating. Although H2L1 is readily deprotonated to the monoanion by potassium metal or potassium hydride, surprisingly we have been unable to form (L1)2. The crystal structure of [K]+[HL1]−·18-crown-6 reveals the potassium ion to be sandwiched between the crown ether (1,4,7,10,13,16-hexaoxacyclooctadecane) and the (HL1)− anion.

Synthesis and structures of organometallic derivatives of 1,2,3,4,5,6,7,8-octamethyl-1,5-dihydro-s-indacene

Scanning tunneling microscopy is used to study the structure of monolayers of tris{2,5-bis(3,5-bis-trifluoromethyl-phenyl)-thieno}[3,4-b,h,n]-1,4,5,8,9,12-hexaaza-triphenylene adsorbed on a clean Ag(110) single-crystal surface. The molecules adsorb flat on the surface, forming two-dimensional islands within which intermolecular interactions constrain the molecules to form rows of molecular pairs. The balance between intermolecular and molecule–substrate interactions leads to two specific orientations of these rows at +11° and −11° from the [001] direction of the Ag(110) surface. A comparison between observed and calculated local densities of states shows an antiparallel azimuthal orientation of the molecules within the closely associated pairs. The structure of the full monolayer shows that the intermolecular interaction overcomes the interaction with the substrate, resulting in a reorientation of the rows along various directions.

Quasi-epitaxy of a Tris(thieno)hexaazatriphenylene Derivative Adsorbed on Ag(110): Structural and Electronic Properties Probed by Scanning Tunneling Microscopy

This work was supported by the Office of Naval Research (N00014- 14-1-0126) and the Air
Force Office of Scientific Research (BIONIC Program,
FA9550-09-1-0162). The author would like to thank Guy
Olivier Ngongang and Kui Zhao for their generous assistance and input regarding photovoltaic and transistor
measurements, and absorbance data modelling.

Stephen Barlow

Papers

Ethylenediamine Addition Improves Performance and Suppresses Phase Instabilities in Mixed-Halide Perovskites

Synthesis and structures of organometallic derivatives of 1,2,3,4,5,6,7,8-octamethyl-1,5-dihydro-s-indacene

Quasi-epitaxy of a Tris(thieno)hexaazatriphenylene Derivative Adsorbed on Ag(110): Structural and Electronic Properties Probed by Scanning Tunneling Microscopy

Ultra-low p-doping of poly(3-hexylthiophene) and its impact on polymer aggregation and photovoltaic performance

Synthesis, crystal structures, and redox behavior of some pentamethylcyclopentadienyl arene ruthenium salts