Developments of High-Efficiency Flexible Cu（In,Ga）Se2 Thin Film Solar Cells on a Polyimide Sheet by Sodium Incorporation

We present the fabrication of flexible Cu（In,Ga）Se2 （CIGS） solar cells on a polyimide （PI） sheet with and without Na incorporation. A sodium element is incorporated into the CIGS absorber by using a NaF precursor after Mo back contact deposition. X-ray diffraction patterns show that the （112） preferred orientation of the as-grown GIGS films is decreased by Na incorporation. The secondary phase of （Inx,Gal-x）zSe3 is observed for the CIGS films with Na. There is no significant difference in the grain size with and without Na incorporation from surface and cross-sectional SEM images. Additionally, the increase of carrier concentration and decrease of resistivity of CIGS absorber are induced by Na doping. Finally, the flexible CIGS solar cells on PI sheets with efficiency close to 11%, containing Na, are achieved. The improvement of cell efficiency can be attributed to the modified electrical properties of the CIGS film by Na incorporation.     

Flexible Cu（In,Ga）Se2 Thin-Film Solar Cells on Polyimide Substrate by Low-Temperature Deposition Process

The electrical and structural properties of polycrystalline Cu（In, Ga）Se2 films grown on polyimide （PI） substrates below 400℃ via one-stage and three-stage co-evaporation process have been investigated by x-ray diffraction spectra （XRD）, scanning electron microscopy （SEM） and Hall effect measurement. As shown by XRD spectra, the stoichiometric CIGS films obtained by one-stage process exhibit the characteristic diffraction peaks of the （In0.68Ga0.32）2Se3 and Cu（In0.7Ga0.3）2Se. It is also found that the film structures indicate more columnar and compact than the three-stage process films from SEM images. The stoichiometric CIGS films obtained by three-stage process exhibit the coexistence of the secondary phase of （In0.68Ga0.32）2Se3, Cu2-xSe and Cu（In0.7Ga0.3）2Se. High net carrier concentration and sheet conductivity are also observed for this kind of film, related to the presence of Cu2-xSe phase. As a result, when the CIGS film growth temperature is below 400℃, the three-stage process is inefficient for solar cells. By using the one-stage co-evaporation process, the flexible CIGS solar cell on a PI substrate with the best conversion efficiency of 6.38% is demonstrated （active area 0.16cm^2）.     

Mo Back Contact for Flexible Polyimide Substrate Cu（In,Ga）Se2 Thin-Film Solar Cells

A dc magnetic sputtering process is applied to growth of a Mo back. contact layer onto the flexible polyimide （PI） and rigid soda-lime glass （SLC） substrates. The structural and electrical properties of the Mo layer coated on the two kinds of substrates are investigated by x-ray diffraction （XRD） and Hall effect measurements. The results show that the Mo layer on SLG indicate more better crystal quality and lower resistivity than that on the PI sheets. In contrast to the SLG substrate, the resistivity of the Mo layer on PI is increased by the vacuum annealing process at the substrate temperature of 450℃ under Se atmosphere, which is attributed to the cracked Mo layer induced by the mismatch of the coefficient of thermal expansion between PI and Mo material. The Cu（In,Ga）Se2 （CIGS） solar cells based on the PI and SLO substrates show the best conversion efficiencies of 8.16% and 10.98% （active area, 0.2cm^2）, respectively. The cell efficiency of flexible CIGS solar cells on PI is limited by its relatively lower fill factor caused by the Mo back contact.     

Effect of Dopant Properties on the Microstructures and Electrical Characteristics of Poly（3-Hexylthiophene） Thin Films

Effects of dopant properties on microstructures and the electrical characteristics of poly （3-hexylthiophene） （P3HT） films are studied by doping 0.1 wt% 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane （F4？TCNQ）, 6,6-phenyl-C61butyric acid methyl ester （PCBM） and N,N＇？Diphenyl-N,N＇-（m-tolyl）-benzidine （TPD） into P3HT, respectively. The introductions of various dopants in small quantities increase the field-effect mobility and the I on/Ioff ratio of P3HT thin-film transistors. However, each of dopants shows various effects on the crystalline order and the molecular orientation of P3HT films and the performance of P3HT thin-film transistors. These can be attributed to the various size, shape and energy-level properties of the dopants.     

Structural and Electrical Characteristics of Pb（Zr0.53,Ti0.47）O3 Thin Films Deposited on Si （100） Substrates

Pb(Zr0.53, Ti0.47)O3 (PZT) films were directly deposited on Si substrates without a buffer layer by pulsed laser deposition. Only(110)-oriented PZT peaks (other than Si substrate peaks) were observed from the XRD data. The electrical properties of the PZT/Si capacitor were characterized in terms of both the capacitance versus voltage (C-V) and current versus voltage (I-V) measurements. The clockwise trace of the C-V curve shows ferroelectric polarization switching, as is expected. From the I-V curves, the Schottky emission and spacecharge-limited-current behaviour are found to be the mainly leakage current mechanism in a certain electric field range in the negative and positive bias, respectively.     

Preparation of Cu（In,Ga）Se2 Thin Film Solar Cells by Selenization of Metallic Precursors in an Ar Atmosphere

Cu（In, Ga）Se2 thin films are deposited on Mo-coated glass substrates by Se vapour selenization of sputtered metallic precursors in the atmosphere of Ar gas flow under a pressure of about 10 Pa. The in situ heat treatment of as-grown precursor leads to the formation of a better alloy. During selenization, the growth of CuInSe2 phase preferably proceeds through Se-poor phases as CuSe and InSe at relatively low substrate temperature of 250℃, due to the absence of In2Se3 at intermediate stage at low reactor pressure. Subsequently, the Cu（In,Ga）Se2 phase is produced by the reactive diffusion of CuInSe2 with a Se-poor GaSe phase at high temperature of up to 560℃. The final film exhibits smooth surface and large grain size. The absorber is used to fabricate a glass/Mo/Cu（In, Ga）Se2/CdS/ZnO cell with the total-area efficiency of about 7%. The low open-circuit voltage value of the cell fabricated should result from the nonuniform distribution of In and Ga in the absorber, due to the diffusion-controlled reaction during the phase formation. The films, as well as devices, are characterized.     

Effect of Temperature on Structural and Magnetic Properties of Laser Ablated Iron Oxide Deposited on Si（100）

We fabricate Fe3O4 thin films on Si（100） substrates at different temperatures using pulsed laser deposition, and study the effect of annealing and deposition temperature on the structural and magnetic properties of Fe3O4 thin films. Subsequently, the films are characterized by x-ray diffraction （XRD）, scanning electron microscopy （SEM） and vibrating sample magnetometery （VSM）. The XRD results of these films confirm the presence of the Fe3O4 phase and show room-temperature ferromagnetism, as observed with VSM. We demonstrate the optimized deposition and annealing conditions for an enhanced magnetization of 854 emu/cm3 that is very high when compared to the bulk sample.     

Performance improvement of CdS/Cu（In,Ga）Se2 solar cells after rapid thermal annealing

In this paper, we investigated the effect of rapid thermal annealing (RTA) on solar cell performance. An opto-electric conversion efficiency of 11.75% (Voc=0.64 V, Jsc = 25.88mA/cm2 , FF=72.08%) was obtained under AM 1.5G when the cell was annealed at 300℃ for 30s. The annealed solar cell showed an average absolute efficiency 1.5% higher than that of the as-deposited one. For the microstructure analysis and the physical phase confirmation, X-ray diffraction (XRD), Raman spectra, front surface reflection (FSR), internal quantum efficiency (IQE), and X-ray photoelectron spectroscopy (XPS) were respectively applied to distinguish the causes inducing the efficiency variation. All experimental results implied that the RTA eliminated recombination centers at the p-n junction, reduced the surface optical losses, enhanced the blue response of the CdS buffer layer, and improved the ohmic contact between Mo and Cu(In, Ga)Se2 (CIGS) layers. This leaded to the improved performance of CIGS solar cell.     

Intrinsic ZnO films fabricated by DC sputtering from oxygen-deficient targets for Cu（In,Ga）Se2 solar cell application

Samples with nodular defects grown from gold nanoparticles are prepared,and laser-induced damage tests are conducted on them.Nodular defects,which are in critical state of damage,are cross-sectioned by focusing on the ion beam and by imaging using a field emission scanning electron microscope.The crosssectional profile shows that cracks are generated and propagated along the nodular boundaries and the HfO2/SiO2 interface,or are even melted.The thermomechanical process induced by the heated seed region is analyzed based on the calculations of temperature increase and thermal stress.The numerical results give the critical temperature of the seed region and the thermal stress for crack generation,irradiated with threshold fluence.The numerical results are in good agreement with the experimental ones.     

Influence of Yb-Doped Nanoporous TiO2 Films on Photovoltaic Performance of Dye-Sensitized Solar Cells

Yb-doped TiO2 pastes with different Yb/TiO2 weight ratios are prepared in the sol-gel process to obtain dyesensitized solar cells （DSCs）. The nanocrystalline size of Yb-TiO2 becomes smaller and the lattice parameters change. Lattice distortion is observed and dark current is detected. It is found that a part of Yb existing as insulating oxide Yb2O3 state acts as barrier layers at the electrode-electrolyte interface to suppress charge recombination. A Yb-doped TiO2 electrode applied in DSCs leads to a higher open-circuit voltage and a higher fill factor. How the Yb-doped TiO2 films affect the photovoltaic response of DSCs is discussed.     

Excellent Passivation of p-Type Si Surface by Sol-Gel Al2O3 Films

Al2O3 films with a thickness of about lOOnm synthesized by spin coating and thermally treated are applied for field-induced surface passivation of p-type crystalline silicon. The level of surface passivation is determined by techniques based on photoconductance. An effective surface recombination velocity below lOOcm/s is obtained on 10Ωcm p-type c-Si wafers （Cz Si）. A high density of negative fixed charges in the order of 10^12 cm^-2 is detected in the Al2O3 films and its impact on the level of surface passivation is demonstrated experimentally. Furthermore, a comparison between the surface passivation achieved for thermal SiO2 and plasma enhanced chemical vapor deposition SiNx ：H films on the same c-Si is presented. The high negative fixed charge density explains the excellent passivation of p-type c-S/by Al2O3.     

Effect of Post-Annealing on Microstructural and Electrical Properties of N^＋Ion-Implanted into ZnO：In Films

We fabricate p-type conductive ZnO thin films on quartz glass substrates by codoping of In-N using radio frequency magnetron sputtering technique together with the direct implantation of acceptor dopants （nitrogen）. The effects of thermal annealing on the structure and electrical properties of the ZnO films are investigated by an x-ray diffractometer （XRD） and a Hall measurement system. It is found that the best p-type ZnO film subjected to annealed exhibits excellent electrical properties with a hole concentration of 1.22 × 10^18 cm^-3, a Hall mobility of 2.19 cm^2 V^-1 s^- 1, and a low resistivity of about 2.33 Ωcm, indicating that the presence of In may facilitates the incorporation of N into ZnO thin films.     

Structural and Magnetic Properties of Fe-Doped Anatase TiO2 Films Annealed in Vacuum

Structural and magnetic properties of Fe-doped anatase TiO2 films fabricated by sol-gel spin coating are investigated. X-ray diffraction measurements reveal that Fe^3＋ ions are incorporated into the TiO2 lattice. No ferromagnetism-related secondary phases and magnetic nanopaxticles are observed in the films. The presence of electron paramagnetic resonance signals at 9- 2.0 supports oxygen vacancies and/or defects generated in the films after annealing in vacuum. Magnetic measurements indicate that Fe-doped anatase TiO2 films are ferromagnetic at room temperature. These observations suggest that oxygen vacancies and/or defects axe energetically favorable for the long range Fe^3＋-Fe^3＋ ferromagnetic coupling in Fe-doped anatase TiO2 films.     

Microstructure of Epitaxial Er2O3 Thin Film on Oxidized Si (111) Substrate

Er₂O₃ thin films are grown on oxidized Si (111) substrates by molecular beam epitaxy. The sample grown under optimized condition is characterized in its microstructure, surface morphology and thickness using grazing incidence x-ray diffraction (GIXRD), atomic force morphology and x-ray reflectivity. GIXRD measurements reveal that the Er₂O₃ thin film is a mosaic of single-crystaldomains. The interplanar spacing d in-plane residual strain tensor ε_| and the strain relaxation degree ξ are calculated. The Poisson ratio μ obtained by conventional x-ray diffraction is in good agreement with that of the bulkEr₂O₃. In-plane strains in three sets of planes, i.e. (440), (404), and (044), are isotropic.     

Resistance Switching Characteristic and Charge Carrier Self-Trapping in Epitaxial Pr0.7（Ca1-xSrx）0.3MnO3 Thin Films

Carrier injection performed in Pro.7 Cao.aMnOa junctions demonstrate resistance switching （RS） characteristic with dramatic changes in both resistances and interface barriers, which suggests a charge carrier self-trapping model in strongly correlated electronic framework. Un-stable RS behaviour without electric fields in epitaxial Pr0.7（Ca1-xSrx）0.3MnO3 （PCSMO） films shows dependences on insulator-metal transition temperature, which indicates that RS process is really related to the intrinsic property of carriers. The switched resistance of epitaxial PCSMO films also depends on the amount of current pulses, which shouM be another evidence of the carrier self-trapping model, similarly to the dependence on the amount of self-trapped charge carriers.     

Effect of Nitridation on Morphology, Structural Properties and Stress of AlN Films

We investigate effects of nitridation on AlN morphology, structural properties and stress. It is found that 3min nitridation can prominently improve AlN crystal structure, and slightly smooth the surface morphology. However, 10min nitridation degrades out-of-plane crystal structure and surface morphology instead. Additionally, 3-min nitridation introduces more tensile stress （1.5 GPa） in AlN films, which can be attributed to the weaker islands 2D coalescent. Nitridation for lOmin can introduce more defects, or even forms polycrystallinity interlayer, which relaxes the stress. Thus, the stress in AlN with 10 min nitridation decreases to -0.2 GPa compressive stress.