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.

Dynamic scaling and optical properties of Zn(S,O,OH) thin film grown by chemical bath deposition

The scaling behavior and optical properties of Zn（S, O and OH） thin films deposited on sod^-lime glass substrates by chemical bath deposition method were studied by combined roughness measurements, scanning electron microscopy and optical properties measurement. From the scaling behaviour, the value of growth scaling exponent β2 0.38±0.06, was determined. This value indicated that the Zn（S, O, OH） film growth in the heterogeneous process was influenced by the surface diffusion and shadowing effect. Results of the optical properties measurements disclosed that the transmittance of the film was in the region of 70%-88% and the optical properties of the film grown for 40 min were better than those grown under other conditions. The energy band gap of the film deposited with 40 min was around 3.63 eV.

The effect of composition on structural and electronic properties in polycrystalline CuGaSe_2 thin film

Polycrystalline CuGaSe2 thin films on Mo-coated soda-lime glass substrates have been synthesized by coevaporation process from Cu, Ga and Se sources. Structural and electrical properties of the as-grown CuGaSe2 films strongly depend on the film composition. Stoichiometric CuGaSe2 is fabricated, as indicated by x-ray diffraction spectroscope （XRD） and x-ray fluorescence （XRF）. A two-phase region is composed of CuGaSe2 and Cu2-xSe phases for Cu-rich films, and CuGaSe2 and CuGa3Se5 phases for Ga-rich films, respectively. Morphological properties are detected by scanning electron microscope （SEM） for various compositional films, the grain sizes of the CuGaSe2films decrease with the extent of deviation from stoichiometric composition. Raman spectroscopy of Cu-rich samples shows that there exist large Cu-Se particles on the film surface. The results from Hall effect measurements for typical samples indicate that CuGaSe2 films are always of p-type semiconductor from Cu-rich to Ga-rich. Stoichiometric CuGaSe2 films exhibit relatively large mobility than any other compositional films. Finally, polycrystalline CuGaSe2 thin film solar cell with a best conversion efficiency of 6.02% has been achieved under the standard air mass （AM）1.5 spectrum for 100mW/cm^2 at room temperature （aperture area, 0.24cm^2）. The open circuit voltage of the CuGaSe2 solar cells is close to770 mV.

Cu（In, Ga）Se2 Thin Films on Flexible Polyimide Sheet： Structural and Electrical Properties versus Composition

The structural and electrical properties of Cu（In,Ga）Se2 （CIGS） films grown on polyimide （PI） sheet using the three-stage co-evaporation process are investigated by x-ray diffraction spectra （XRD）, scanning electron microscopy （SEM）, Raman spectra, and Hall effect measurements, respectively. The results show that the properties of CIGS films on PI sheet are strongly dependent on the compositional ratio of Cu/（In＋Oa） （Cu/Ⅲ）. In contrast to the non-stoichiometric CIGS films, stoichiometric CIGS films show better structural and electrical properties, such as a relatively larger grain size, lower resistivity and higher carrier concentration. The flexible CIGS solar cells on PI sheet with the conversion efficiencies of 9.7% and 6.6% are demonstrated for the CIGS absorber layer with Cu/Ⅲ of 0.96 and 0.76, respectively （active area, 0.20cm^2）. The cell efficiency for Cu-poor CIGS films is limited by a relatively lower open circuit voltage and fill factor.

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.

CuInSe2 Films Prepared by a Plasma-Assisted Selenization Process in Different Working Pressures

The effects of working pressure on the composition, structure and surface morphology properties of CuInSe2 （CIS） films selenized with a plasma-assisted selenization process is investigated. Higher selenium content, better crystalline quality and much more regular surface particles compared to the others are found in the CIS film with 40 Pa working pressure. A Cu（In,Ga）Se2 device fabricated with the optimized plasma-assisted selenization process is demonstrated to be better than our previous result. After discussion, the reason for these phenomena is attributed to the compromise of electron temperature and plasma density.

OLED-on-silicon chip with new pixel circuit

A low power 640×480 OLED-on-silicon chip design that used in microdisplay was presented. A novel pixel circuit was proposed to meet the special requirement of OLED-on-silicon. The novel pixel consists of three transistors and one capacitor （3T 1C）. It has simple structure and can effectively reduce the current glitch generated during the AC driving from 55 pA to 7.5 pA, so that it can improve the precision of grayscale of display as well as extend the lifetime of （]）LED material. Except for the pixel array, low power row driver, column driver and other functional modules were also integrated on the chip. Several techniques were adopted to reduce the power consumption and frequency requirement of the chip. Finally, a 16×3×12 resolution chip was fabricated with standard 0.35 μm CMOS process of CSM and the chip can operate correctly.

Influence of growth temperature and thickness on the orientation of Cu(In,Ga)Se_2 film

Cu(In,Ga)Se2(CIGS) films are deposited on the Na-free glass substrate using three-stage co-evaporation process,and the effects of thickness and growth temperature on the orientation of CIGS film are investigated by X-ray diffraction(XRD) and scanning electron microscopy(SEM).When the growth of CIGS film does not experience the Cu-rich process,the increase of the growth temperature at the second stage(Ts2) promotes the(112) orientation of CIGS film,and weakens the(220) orientation.Nevertheless,when the growth of CIGS film experiences Cu-rich process,the increase of Ts2 significantly promotes the(220) orientation.In addition,with the thickness of CIGS film decreasing,the extent of(In,Ga)2Se3(IGS) precursor orientation does not change except for the intensity of Bragg peak,yet the(220) orientation of following CIGS film is hindered,which suggests that(112) plane preferentially grows at the initial growth of CIGS film.

Restraining for switching effects in an AC driving pixel circuit of the OLED-on-silicon

The AC driving scheme for OLEDs,which uses the pixel circuit with two transistors and one capacitor(2T1C),can extend the lifetime of the active matrix organic light-emitting diode(AMOLED) on silicon,but there are switching effects during the switch of AC signals,which result in the voltage variation on the storage capacitor and cause the current glitch in OLED.That would decrease the gray scale of the OLED.This paper proposes a novel pixel circuit consisting of three transistors and one capacitor to realize AC driving for the OLED-on-silicon while restraining the switching effects.Simulation results indicate that the proposed circuit is less sensitive to switching effects.Also,another pixel circuit is proposed to further reduce the driving current to meet the current constraints for the OLED-on-silicon.

Fabrication of high-quality ZnS buffer and its application in Cd-free ClGS solar cells

This paper provides the fabrication of Cd-free Cu（In,Ga）Se2 （CIGS） solar cells on soda-lime glass substrates. A high quality ZnS buffer layer is grown by chemical bath deposition （CBD） process with ZnSO4-NH3-SC （NH2）2 aqueous solution system. The X-ray diffraction （XRD） result shows that the as-deposited ZnS film has cubic （111） and （220） diffraction peaks. Scanning electron microscope （SEM） images indicate that the ZnS film has a dense and compact surface with good crystalline quality. Transmission measurement shows that the optical transmittance is about 90% when the wavelength is beyond 500 nm. The bandgap （Eg） value of the as-deposited ZnS film is estimated to be 3.54 eV. Finally, a competitive efficiency of 11.06% is demonstrated for the Cd-free CIGS solar cells with ZnS buffer layer after light soaking.

Fabrication of high-quality ZnS buffer and its application in Cd-free CIGS solar cells

This paper provides the fabrication of Cd-free Cu(In,Ga)Se2(CIGS) solar cells on soda-lime glass substrates. A high quality ZnS buffer layer is grown by chemical bath deposition(CBD) process with ZnSO4-NH3-SC(NH2)2 aqueous solution system. The X-ray diffraction(XRD) result shows that the as-deposited ZnS film has cubic(111) and(220) diffraction peaks. Scanning electron microscope(SEM) images indicate that the ZnS film has a dense and compact surface with good crystalline quality. Transmission measurement shows that the optical transmittance is about 90% when the wavelength is beyond 500 nm. The bandgap(Eg) value of the as-deposited ZnS film is estimated to be 3.54 eV. Finally, a competitive efficiency of 11.06% is demonstrated for the Cd-free CIGS solar cells with ZnS buffer layer after light soaking.

Low power design of a field sequential color LCoS chip

The low power design of a field sequential color (FSC) liquid crystal on silicon (LCoS) chip for near-to-eye application is presented in this paper. Dual power supplies are used in the design,that is,the supply for part of driving circuits is 3.3 V,and the one for the active matrix is 5.0 V. Serial-to-parallel conversion circuits are adopted to lower the pixel clock frequency of the chip. Also,an idle state is inserted into the pixel clock signal to decrease the switching activity factor to further reduce the power consumption. The LCoS chip is fabricated with 0.35 μm CMOS process and its power consumption is only about 300 mW.