A Photovoltaic C60-Si Heterojunction

Abstract

A heterojunction was prepared by depositing a thin film of C₆₀ on a p-Si substrate. Photovoltaic properties were observed using a UV-filtered solar simulator and natural sun light. Surface Photovoltage Spectroscopy was employed to distinguish between the nature of photoconversion in the C₆₀ and Si layers.     

基于p+-Si与n-ZnO纳米线的p-n异质结的制备及其性质研究

利用CVD蒸汽俘获法，在p^＋硅片上制备了垂直生长的n型ZnO纳米线阵列，用XRD和SEM分析了样品的结构与形貌。测试发现样品的I-V曲线符合典型的p-n异质结特性，正向开启电压为0．5V，反向饱和电流为0．02mA。计算了异质结的理想因子η，发现当异质结两端偏压在0V-0．3V的低压区域，理想因子为1．85，而在0．3v-0．8v的高偏压区域，理想因子为8．36。解释了理想因子偏高的原因是由于金属一半导体接触以及ZnO纳米线与p^＋-si界而存在缺陷。     

Intramolecular Negative-Effect in the Alkali-Metal-Doped C60; A2C60 and A4C60

It is investigated theoretically why alkali-metal-doped C₆₀, A_xC₆₀, is a nonmagnetic semiconductor for x=2 and 4. We find that this is the consequence of the intramolecular negative- U effect due to the strong electron-phonon interaction and the weak Hund coupling between conduction electrons.     

The Bulk Heterojunction in Organic Photovoltaic,Photodetector, and Photocatalytic Applications

Organic semiconductors require an energetic offset in order to photogenerate free charge carriers efficiently, owing to their inability to effectively screen charges. This is vitally important in order to achieve high power conversion efficiencies in organic solar cells. Early heterojunction-based solar cells were limited to relatively modest efficiencies (<4%) owing to limitations such as poor exciton dissociation, limited photon harvesting, and high recombination losses. The development of the bulk heterojunction (BHJ) has significantly overcome these issues, resulting in dramatic improvements in organic photovoltaic performance, now exceeding 18% power conversion efficiencies. Here, the design and engineering strategies used to develop the optimal bulk heterojunction for solar-cell, photodetector, and photocatalytic applications are discussed. Additionally, the thermodynamic driving forces in the creation and stability of the bulk heterojunction are presented, along with underlying photophysics in these blends. Finally, new opportunities to apply the knowledge accrued from BHJ solar cells to generate free charges for use in promising new applications are discussed.     

退火温度对ZnO/Si异质结光电转换特性的影响

采用直流反应溅射法在P-Si(100)衬底上制备了ZnO薄膜,XRD测量表明ZnO为沿c轴高度取向的多晶薄膜,1-V特性曲线表明,ZnO/Si异质结具有明显的整流特性.研究了退火温度对异质结光电转换特性的影响,结果显示,合适的退火温度能显著增大异质结的开路电压和短路电流,进而增大异质结的光电转换效率,经400℃退火后异质结获得最佳的转换效率.当退火温度达到或超过500℃时,异质结的反向电流迅速增加,光生电压和光生电流大幅度减小.通过对ZnO薄膜结构和电学性质的测量和分析,推测异质结的光电转换特性改变主要受ZnO薄膜的电学性质影响.     

Au电极作用下C60、2C60与4C60富勒烯分子的电子传输特性

采用扩展的Hückel方法与格林函数方法,研究了Au电极作用下,C60富勒烯、2C60和4C60聚合体分子的电子结构与导电性,并对它们的电子结构与电子输运特性进行了对比.研究结果表明,C60、2C60或4C60富勒烯分子与Au电极 "接触"后,其HOMO、LUMO间的能隙减小;C60、2C60或4C60分子与Au电极之间的结合既有共价键的成分,又有离子键的成分,其中,C60、4C60分子与Au电极结合的离子键特征更为明显;三种富勒烯分子的电子输运性能依次具有C60>2C60>4C60分子的顺序.     

Impact of Solvent Additive on Carrier Transport in Polymer:Fullerene Bulk Heterojunction Photovoltaic Cells

The effects of a solvent additive, 1,8‐diiodooctane (DIO), on both hole and electron transport are investigated in a state‐of‐the‐art bulk‐heterojunction (BHJ) system, namely PTB7:PC₇₁BM. For a polymer:fullerene weight ratio of 1:1.5, the electron mobility in the blend film increases by two orders of magnitude with the DIO concentration while almost no change is found in the hole mobility. For lower DIO concentrations, the electron mobility is suppressed because of large, but poorly connected PC₇₁BM domains. For higher concentrations of DIO, the electron mobility is improved progressively and the hole mobility becomes the limiting factor. Between 1 and 5 vol%, the electron and hole mobilities are balanced. Using the Gaussian disorder model (GDM), we found that the DIO concentration modifies fundamentally the average hopping distances of the electrons. In addition, there exist alternative donor–acceptor ratios to achieve optimized PTB7:PC₇₁BM based solar cells. It is demonstrated that the fullerene content of the BHJ film can be significantly reduced from 1:1.5 to 1:1 while the optimized performance can still be preserved.     

Electronic structure and electrical transport characteristics of C60, 2C60 and 4C60 fullerene molecules

The extended H?ckel method and the Green s function method were used to calculate the electronic structure and electrical transport of Au electrode-C₆₀, 2C₆₀ or 4C₆₀ fullerene-Au electrode systems. Furthermore, their electronic structure and electrical transport characteristics were compared and analyzed. The results show that (i) owing to the contact with the Au electrodes, the C₆₀, 2C₆₀ and 4C₆₀ molecules change in their electronic structures significantly, and their energy gaps between LUMO and HOMO are narrow; (ii) the bonding between C₆₀, 2C₆₀ or 4C₆₀ fullerene and Au electrodes is partially covalent and partially electrovalent; and (iii) the conductance of the three fullerenes conforms to the order of C₆₀>2C₆₀>4C₆₀.     

A Study of Interaction of Dopants in C60: Doping Alkali-Halogen-Alkali into C60 in Successive Steps

It is well established that for an alkali-doped C₆₀ sample to be superconducting, the oxidation state C ^3– ₆₀ must be satisfied. It has been found previously that T _c is proportional to crystal parameter a in a face-centered cubic (fcc) structure. It is thus desirable to intercalate the largest possible size of molecule that can contribute one electron into every interstitial space. The successful process of such doping depends on our understanding the interaction among the dopants and C₆₀. We introduce a fabrication scheme of three steps successive doping using alkali (A) and halogen (H) elements along this line. While A ₃C₆₀ is superconducting, A _3–x (AH) _x C₆₀ was found to be non-superconducting in the second step and the sample became superconducting again after doping with A, leading to stoichiometric ratio of A _3–x (AH) _x A _x C₆₀. We present an explanation based on interaction among dopants and C₆₀ and analyze the process of ionization of dopants, which is consistent with our experimental finding reported here.     

Ozonides and Oxides of C60 and C70: A Review

This paper presents a literature review of studies of ozonides and oxides of C₆₀ and C₇₀.