The effect of post-annealing on the interface between the aluminum electrode and the active layer in polymer/fullerene solar cells

The post-annealing effects on the performance of poly (3-hexylthiophene) (P3HT)/(6,6)-phenyl C₆₁ butyric acid methyl ester (PCBM) solar cells with conventional bulk heterojunction (CBHJ) and layer-evolved bulk heterojunction (LBHJ) have been compared. It is found that contrary to the much better performance obtained from CBHJ cells, the post-annealing deteriorates the performance of LBHJ devices. Aqueous contact angle and X-ray photoelectron spectroscopy measurements show that P3HT is dominant at the top surface of CBHJ film, while PCBM is dominant at the top surface of LBHJ film. The micron-scale morphology evolution of the active layer/Al interface upon post-annealing reveals that the PCBM-rich surface is beneficial for the nucleation and growth of PCBM crystal, which does harm to the contact between the active layer and the electrode and results in the decrease of the fill factor. However, the original P3HT-rich surface prevents the formation of large surface-segregated PCBM clusters upon post-annealing, which is highly desirable for the efficient polymer/fullerene solar cells.     

Combined analysis of near-threshold production of ω and φ mesons in nucleon-nucleon collisions within an effective meson-nucleon model

Vector meson ( V = ,) production in near-threshold elementary nucleon-nucleon collisions ppppV, pnpnV and pndV is studied within an effective meson-nucleon theory. It is shown that a set of effective parameters can be established to describe fairly well the available experimental data of angular distributions and the energy dependence of the total cross-sections without explicit implementation of the Okubo-Zweig-Iizuka rule violation. Isospin effects are considered in detail and compared with experimental data whenever available.     

Renormalization group calculation of the critical temperature dependence on longitudinal magnetic field for a disordered superconductor model

We describe a calculation ofT _c (P, H) in a model of a disordered superconductor which is based on the de Gennes-Skal-Shklovskii (dGSS) picture of the large cluster in a percolation system. The calculation is done by carrying out successive decimations on the Landau-Ginzburg Hamiltonian describing the links in the model. We calculateT _c (P, H) in the presence of longitudinal magnetic field by evaluating the renormalized Landau-Ginzburg coupling when the renormalized Landau-Ginzburg length equals the percolation link length in the dGSS picture and obtain the approximate analytic form ofT _c (P, H).Work supported by China Natural Science Foundation     

Optimum ratio of electron-to-hole mobility in P3HT:PCBM organic solar cells

We investigate the influence of different electron-to-hole mobility ratios on the performance of a P3HT:PCBM bulk heterojunction organic solar cell by using numerical simulations. We show that in some particular mobility cases using a ratio between electron and hole mobility higher than one can improve power conversion efficiency.     

Photon production in nucleon-nucleon collisions

We calculate the differential cross section for nucleonnucleon bremsstrahlung in covariant way based on a realistic meson-exchange approximation for the NN-scattering amplitude. The results are discussed in comparison to semiclassical approximations and with respect to the role of internal radiation diagrams. The influence of the anomalous magnetic moment on the proton-neutron bremsstrahlung is found to contribute up to 50% for specific kinematical conditions. Recent measurements on the elementary differential cross sectionpnpn are found to be quite accurately reproduced. Furthermore, for use in proton-nucleus and nucleus-nucleus collisions, we present a parametrization of thepn cross section within a broad kinematical range.Work supported by BMFT, GSI Darmstadt and a NATO science grant     

Backbends in Directed Percolation

When directed percolation in a bond percolation process does not occur, any path to infinity on the open bonds will zigzag back and forth through the lattice. Backbends are the portions of the zigzags that go against the percolation direction. They are important in the physical problem of particle transport in random media in the presence of a field, as they act to limit particle flow through the medium. The critical probability for percolation along directed paths with backbends no longer than a given length n is defined as p _n. We prove that (p _n) is strictly decreasing and converges to the critical probability for undirected percolation p _c. We also investigate some variants of the basic model, such as by replacing the standard d-dimensional cubic lattice with a (d–1)-dimensional slab or with a Bethe lattice; and we discuss the mathematical consequences of alternative ways to formalize the physical concepts of percolation and backbend.     

High-resolution normal emission UV-photoelectron spectra and band structure of Cu

The energy distribution curves of photoelectrons emitted along the normal direction from Cu (111), (001) and (110) surfaces using unpolarized HeI (hv=21.2 eV) and HeII (hv=40.8 eV, 48.4 eV) radiation incident at 45° to the surface were measured. For the interpretation the band structure as calculated by Janak et al. and by the combined interpolation scheme was used. The high resolution spectra along the [111] and [001] directions show dominant features from direct transitions, indicating strong residualk _z conservation, and density of states features, too. The band gap emission along the [110] direction using HeI radiation can be explained with direct transitions into evanescent states with nearly free electron bands. From the width of the peaks electron escape depths were calculated.     

NN final-state interaction in two-nucleon knockout from <Superscript>16</Superscript><Emphasis Type="Italic">O</Emphasis>

The influence of the mutual interaction between the two outgoing nucleons (NN-FSI) in electro- and photoinduced two-nucleon knockout from ¹⁶O has been investigated perturbatively. It turns out that the effect of NN-FSI depends on the kinematics and on the type of reaction considered. The effect is generally larger in pp- than in pn-knockout and in electroinduced than in photoinduced reactions. In superparallel kinematics NN-FSI leads in the (e,epp) channel to a strong increase of the cross-section, that is mainly due to a strong enhancement of the -current contribution. In pn-emission, however, this effect is partially cancelled by a destructive interference with the seagull current. For photoreactions NN-FSI is considerably reduced in superparallel kinematics and can be practically negligible in specific kinematics.Received: 1 July 2003, Published online: 10 February 2004PACS: 13.75.Cs Nucleon-nucleon interactions (including antinucleons, deuterons, etc.) - 21.60.-n Nuclear structure models and methods - 25.30.Fj Inelastic electron scattering to continuum     

基于透射率曲线确定聚合物太阳能电池功能层的光学常数和厚度

本文介绍了一种确定聚合物太阳能电池功能层光学常数和厚度的方法. 该方法借助于特定的色散模型拟合透射率测试曲线以获得功能层光学常数和厚度值. 文中比较了Forouhi-Bloomer和Lorentz-Oscillator模型在体异质结薄膜的透射率拟合计算中的适用性, 计算了poly(3-hexylthiophene)(P3HT)/[6,6]-phenylC₆₁-butyric acid methyl ester (PCBM)和 poly[2-methoxy-5-5(2'-ethyl-hexyloxy)-1,4-phenylenevinylene](MEH-PPV)/PCBM体异质结薄膜的光学常数和厚度. 拟合得到的曲线与实验曲线符合良好, 厚度计算的结果与台阶仪测量结果保持一致, 误差小于4%. 进一步分析得到的热退火和加入高沸点溶剂添加剂后P3HT/PCBM薄膜的光学常数和光学禁带值与相应器件伏安特性相符. 该方法适用于所有体异质结的功能层, 可用于聚合物太阳能电池的膜系优化和在线检测.     

Representations of (1,0) and (2,0) Superconformal Algebras in Six Dimensions: Massless and Short Superfields

We construct unitary representations of (1,0) and (2,0) superconformal algebras in six dimensions by using superfields defined on harmonic superspaces with coset manifolds USp(2n)/[U(1)]ⁿ, n=1, 2. In the spirit of the AdS₇/CFT₆ correspondence, massless conformal fields correspond to supersingletons in AdS₇. By tensoring them we produce all short representations corresponding to 1/2 and 1/4 BPS anti-de Sitter bulk states of which massless bulk representations are particular cases.     

Performance improvement of MEH-PPV:PCBM solar cells using bathocuproine and bathophenanthroline as the buffer layers

In this work, bathocuproine (BCP) and bathophenanthroline (Bphen), commonly used in small-molecule organic solar cells (OSCs), are adopted as the buffer layers to improve the performance of the polymer solar cells (PSCs) based on poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV): [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) bulk heterojunction. By inserting BCP or Bphen between the active layer and the top cathode, all the performance parameters are dramatically improved. The power conversion efficiency is increased by about 70% and 120% with 5-nm BCP and 12-nm Bphen layers, respectively, when compared with that of the devices without any buffer layer. The performance enhancement is attributed to BCP or Bphen (i) increasing the optical field, and hence the absorption in the active layer, (ii) effectively blocking the excitons generated in MEH-PPV from quenching at organic/aluminum (Al) interface due to the large band-gap of BCP or Bphen, which results in a significant reduction in series resistance (Rs), and (iii) preventing damage to the active layer during the metal deposition. Compared with the traditional device using LiF as the buffer layer, the BCP-based devices show a comparable efficiency, while the Bphen-based devices show a much larger efficiency. This is due to the higher electron mobility in Bphen than that in BCP, which facilitates the electron transport and extraction through the buffer layer to the cathode.     

Thed-p model of ‘highT c’ superconductivity is the Anderson lattice

We show that thed-p model of HighT _c superconductivity can be mapped ontoa spin half Anderson latticewith vanishing conduction electron band width. Using the non-orthogonal basis of Zhang and Rice [1], we show that the orthogonalised combinations are very short range and make up a conduction band for the resulting Anderson Lattice. The only motion is restricted to that with achange of orbital character.     

Cluster Structure of Collapsing Polymers

In order to better understand the geometry of the polymer collapse transition, we study the distribution of geometric clusters made up of the nearest neighbor interactions of an interacting self-avoiding walk. We argue for this new correlated percolation problem that in two dimensions, and possibly also in three dimensions, a percolation transition takes place at a temperature lower than the collapse transition. Hence this novel transition should be governed by exponents unrelated to the -point exponents. This also implies that there is a temperature range in which the polymer has collapsed, but has no long-range cluster structure. We use Monte Carlo to study the distribution of clusters on the simple cubic and Manhattan lattices. On the Manhattan lattice, where the data are most convincing, we find that the percolation transition occurs at _p =1.461(3), while the collapse transition is known to occur exactly at =1.414.... We propose a finite-size scaling form for the cluster distribution and estimate several of the critical exponents. Regardless of the value of _p , this percolation problem sheds new light on polymer collapse.     

Some problems of quantum mechanics possessing a non-negative phase-space distribution function

In order to clarify physical consequences due to the presence of a set of auxiliary functions _k (q,t) in quantum mechanics with a non-negative phase-space distribution function, the simplest quantum-mechanical problems are solved. It is shown that _k (q,t) influence upon the results of a problem. Therefore it is supposed that _k (q, t) reflect some physical reality (subquantum situation), interacting with a mechanical system. In particular the subquantum situation determines the minimum coordinate and momentum uncertainties ((q)² and (p)²) as well as the coordinate distribution of a fixed system and the momentum distribution of a free system. These results provide the opportunity to formulate the notion of a stationary homogeneous isotropic subquantum situation. Supposing thatq andp are small an attempt is made to develop an approximate method of solutions (quasi-orthodox approximation). Energy spectrum of an electron in a hydrogen atom is found in the second order of this approximation.On leave of absence from Peoples' Friendship University, Chair of Theoretical Physics, 3, Ordjonikidze Street, B-302, Moscow, U.S.S.R.     

在电子传输层中添加PVK提高钙钛矿太阳能电池的性能

为了探究PVK对倒置平面异质结钙钛矿太阳能电池电子传输层的影响,向电子传输层PCBM中添加了一种富电子的聚乙烯基咔唑(PVK).采用原子力显微镜、PL光谱对薄膜进行了表征.实验结果表明:少量PVK的添加提高了覆盖在钙钛矿薄膜上PCBM层的平整度.当PVK的添加质量分数为4%时得到最佳器件效率,相比于纯PCBM作为电子传输层的器件,器件效率由(5.11±0.14)% 提升到(9.08±0.46)%.当PVK的添加质量分数大于4%时,粗糙度又趋于变大.PL光谱显示,少量PVK的加入使钙钛矿/电子传输层薄膜的PL强度降低,并使PL峰蓝移.研究表明:向PCBM中掺杂适量PVK能够改善钙钛矿/电子传输层/Al的界面接触,减少漏电流,并能够减少钙钛矿表面陷阱和晶界缺陷,减少电荷复合,从而提高了器件性能.     

Percolation and scaling on a quasilattice

We report results of a study of percolation on a two-dimensional Penrose quasilattice. After an extensive numerical analysis, we find that two-dimensional universality is obeyed. The scaling exponents and have the values expected,=2.04 and=0.39, consistent with the universality class for percolation on a 2D periodic lattice. But the percolation thresholdp _c=0.483, differs from other 2D lattices with the same average coordination number ¯z=4.We dedicate this paper to the memeory of Marc Kac. One of us (J.L.B.) had the good fortune to known him on many levels: as friend, fellow scientist, and co-worker for human rights. His insight, wisdom, and compassion will remain with us as a lasting legacy of his life.     

Asymptotic Completeness for Compton Scattering

Scattering in a model of a massive quantum-mechanical particle, an electron, interacting with massless, relativistic bosons, photons, is studied. The interaction term in the Hamiltonian of our model describes emission and absorption of photons by the electron; but electron-positron pair production is suppressed. An ultraviolet cutoff and an (arbitrarily small, but fixed) infrared cutoff are imposed on the interaction term. In a range of energies where the propagation speed of the dressed electron is strictly smaller than the speed of light, unitarity of the scattering matrix is proven, provided the coupling constant is small enough; (asymptotic completeness of Compton scattering). The proof combines a construction of dressed one–electron states with propagation estimates for the electron and the photons.Dedicated to Freeman Dyson on the occasion of his 80th birthdayWork partially supported by U.S. National Science Foundation grant DMS 01-00160.Acknowledgement. We thank V. Bach for his hospitality at the University of Mainz, where part of this work was done, and we are indebted to Gian Michele Graf for pointing out a serious gap in an earlier version of this paper. We also thank one of the referees for pointing out many typos and some small errors.     

平面异质结有机-无机杂化钙钛矿太阳电池研究进展

高效低成本太阳电池的研发是太阳能光伏技术大规模推广应用的关键. 近年来兴起的有机- 无机杂化钙钛矿(以下简称钙钛矿)太阳电池因具有光电能量转换效率高、制备工艺简单等优点, 引起了学术界和产业界的广泛关注, 具有广阔的发展前景. 其中平面异质结钙钛矿太阳电池因具有结构简单, 可低温制备等诸多优点, 成为目前研究的一个重要方向. 平面异质结钙钛矿太阳电池分为n-i-p型和p-i-n型两种结构. 其中钙钛矿分别与电子传输层和空穴传输层形成两个界面, 在这两个界面上实现电子和空穴的快速分离. 电子传输层和空穴传输层分别为电子和空穴提供了独立的输运通道. 平面异质结结构有利于钙钛矿太阳电池中电子和空穴的分离、传输和收集. 此外, 该结构不需要高温烧结的多孔结构氧化物骨架, 扩大了电子和空穴传输材料的选择范围. 可以根据钙钛矿材料的能带分布及载流子传输特性, 来选择能级和载流子传输速率更为匹配的传输材料. 本文对钙钛矿的材料特性, 平面异质结结构的由来及发展进行了简要的概述. 其中重点介绍了平面异质结钙钛矿太阳电池的结构特征、工作机理、钙钛矿/电荷传输层的界面特性, 以及电池性能的优化, 包括钙钛矿薄膜制备、空穴和电子传输层的优化等. 最后对钙钛矿电池的发展前景及存在问题进行了阐述, 为今后高效、稳定钙钛矿太阳电池的研究提供参考.     

Perturbed periodic Hamiltonians: Essential Spectrum and exponential decay of eigenfunctions

Spectral properties of – +V(x), whereV(x) lies in a neighbourhood of the periodic case and describes various models of disorder, are studied. We prove the exponential decay of generalized eigenfunctions corresponding to energies in the resolvent set of the unperturbed periodic Hamiltonian, as well as the stability of the essential spectrum for the dislocation disorder in two dimensions.     

Excitation functions and isomeric ratios in the reaction130Te (α,xpyn) for α-particle energies between 15 and 37 MeV

The¹³⁰Te(,n)¹³³Xe,¹³⁰Te(,p)¹³³I,¹³⁰Te(,pn)¹³²I and¹³⁰Te(, n)¹²⁹Te excitation functions for alpha particle energies between 14.7 and 36.5 MeV are presented. Excitation functions for the last three reactions are measured for the first time and more consistent results for (, n) are obtained. The isomeric ratios for the ( n), (, pn) and (, n) reactions were deduced. Calculations based on different theoretical models of equilibrium and preequilibrium decay are compared with the experimental results and discussed. Acceptable presentation of the energy behavior of the measured isomeric ratios was obtained when higher angular momentum depletion for preequilibrium emitted particles was included. The absolute values of the isomeric ratios however remain overestimated.We want to express our gratitude to Prof. Ts. Vylov and Dr. V. Brudanin (Dubna) who supplied us with measurement equipment, to Dr. Chr. Necheva for taking part in the experiments, to the U-200 cyclotron staff and to the direction of the Laboratory of Nuclear Reactions (JINR) for making the irradiation possible and to Dr. E. Dobreva (Sofia) for fruitful discussion of the experimental method. We wish to express our gratitude also to Prof. M. Uhl and the NEA data bank for making the computer code STAPRE available to us and to Prof. J. Ernst (Bonn) for fruitful discussions. This project has been completed with the financial support of the Committee for Science at the Council of Ministers under contract No. 644.