Can the incident photo-to-electron conversion efficiency be used to calculate short-circuit current density of dye-sensitized solar cells

The relationship between the integration of the incident photo-to-electron conversion efficiency (IPCE) and the measured short-circuit current density (J_SC) of dye-sensitized solar cell (DSC) has been analyzed. The J_SC of DSC under full sun is usually considered to be determined by the overlap between its spectral IPCE and the spectral photon flux incident on the cell. However, the IPCE spectrum has been found to be influenced by the bias light intensity in many practical cases. Through theoretical deduction, we have proved that J_SC calculated from IPCE spectrum is related to the slope at corresponding incident light intensity on the short-circuit photocurrent density–incident light intensity (J_SC?E_light) curve. The equal relation between J_SC calculated from IPCE and J_SC practically measured can only be obtained when the J_SC?E_light curve is a straight line through the origin of the coordinates. The measured results of four DSC samples with different working condition show a good agreement with the theory. In addition, a simple method to validate the accuracy of IPCE measurement is also demonstrated.     

Effect of surface roughness of TiO2 films on short-circuit current density of photoelectrochemical cell of ITO/TiO2/PVC-LiClO4/graphite

This paper reports the effect of surface topography of titanium dioxide films on short-circuit current density of photoelectrochemical solar cell of ITO/TiO₂/PVC-LiCLO₄/graphite. The films were deposited onto ITO-covered glass substrate by screen-printing technique. The films were tempered at 300 °C, 350 °C, 400 °C, 450 °C and 500 °C for 30 min to burn out the organic parts and to achieve the films with porous structure. The surface roughness of the films were studied using scanning electron microscope (SEM). Current–voltage relationship of the devices were characterized in dark at room temperature and under illumination of 100 mW cm⁻² light from tungsten halogen lamp at 50 °C. The device utilising the TiO₂ film annealed at 400 °C produces the highest short-circuit current density and open-circuit voltage as it posses the smoothest surface topography with the electrolyte. The short-circuit current density and open-circuit voltage of the devices increase with the decreasing grain size of the TiO₂ films. The short-circuit current density and open-circuit voltage are 0.6 μA/cm² and 109 mV respectively.     

缓冲夹层影响异质结有机光伏器件性能研究

制备了结构为CuPc/缓冲层/C₆₀异质结的有机光伏器件,分别选用三氧化钼和红荧烯为缓冲层,研究了增加缓冲层对器件性能的影响.结果表明,增加三氧化钼和红荧烯缓冲层后器件的开路电压和光电转换效率都得到提高,器件的短路电流密度和填充因子都有所降低.开路电压从没有缓冲层时的0.39 V分别提高到0.58 V、0.55 V,转换效率从0.36%提高到0.44%,短路电流从1.92 mA/cm²分别降低到1.77 mA/cm²、1.81 mA/cm²,填充因子从0.48分别减少到0.43、0.44.进一步研究表明器件的短路电流密度受缓冲层厚度的影响很大,当缓冲层厚度很小时,器件短路电流密度还有所增加,但随着缓冲层厚度的增加,短路电流密度逐渐减小,当缓冲层厚度为10 nm时,器件短路电流密度减少到0.35 mA/cm².开路电压随着厚度的增加逐渐增加,从1 nm时的0.43 V增加10 nm时0.63 V.根据整数电荷转移模型和界面能级理论解释有机光伏器件开路电压提高以及短路电流密度减少的原因,为有机太阳能电池性能的改善提供了研究方法.     

低温超薄高效Cu(In,Ga)Se2太阳电池的实现

衬底温度保持恒定, 在Se气氛下按照一定的元素配比顺序蒸发Ga, In, Cu制备厚度约为0.7 μrm的Cu(In_0.7Ga_0.3)Se₂ (CIGS)薄膜. 利用X射线衍射仪分析薄膜的晶体结构及物相组成, 扫描电子显微镜表征薄膜形貌及结晶质量, 二次离子质谱仪测试薄膜内部元素分布, 拉曼散射谱 分析薄膜表面构成, 带积分球附件的分光光度计测量薄膜光学性能. 研究发现在Ga-In-Se预制层内, In主要通过晶界扩散引起Ga/(Ga+In)分布均匀化. 衬底温度高于450 ℃时, 薄膜呈现单一的Cu(In_0.7Ga_0.3)Se₂相; 低于400℃, 薄膜存在严重的Ga的两相分离现象, 且高含Ga相主要存在于薄膜的上下表面; 低于300 ℃, 薄膜结晶质量进一步恶化. 薄膜表层的高含Ga相Cu(In_0.5Ga_0.5)Se₂以小晶粒形式均匀分布于薄膜表面, 增加了薄膜的粗糙度, 在电池内形成陷光结构, 提高了超薄电池对光的吸收. 加上带隙值较小的低含Ga相的存在, 使电池短路电流密度得到较大改善. 衬底温度在550 ℃–350 ℃变化时, 短路电流密度J_SC是影响超薄电池转换效率的主要因素; 而衬底温度T_sub低于300 ℃时, 开路电压V_OC和填充因子FF降低已成为电池性能减退的主要原因. T_sub为350 ℃时制备的0.7 μm左右的超薄CIGS电池转换效率达到了10.3%. 关键词： 2薄膜')" href="#">Cu(In,Ga)Se₂薄膜 衬底温度 超薄 太阳电池     

Characteristics of a type-II n-MoS2/p-Ge van der Waals heterojunction

A few-atomic-layer molybdenum disulfide (MoS₂) film on Si/SiO₂ substrates grown by metal-organic chemical vapor deposition was investigated. The few-atomic-layer MoS₂ film was subsequently transferred onto a (100) p-Ge substrate to build a van der Waals n-p heterojunction. The as-grown few-atomic-layer MoS₂ film and the MoS₂/Ge heterostructure were characterized atomic force microscopy, spectroscopic ellipsometry, high-resolution scanning transmission electron microscopy, Raman spectroscopy analyses, photoluminescence (PL) measurements at room temperature (RT, 300 K), and type-II band alignment of the heterostructure determined by ultraviolet photoelectron spectroscopy. The RT-PL measurements showed dominant peaks at 1.96 and 1.8 eV for the as-grown MoS₂ and red-shifted PL peaks for that transferred onto Ge. We examined the electrical characteristics of the few-atomic-layer MoS₂ by forming a type-II band alignment van der Waals heterojunction with a highly doped p-Ge. The heterojunction solar cell exhibited an open-circuit voltage of 0.15 V and a short-circuit current density of 45.26 μA/cm². The external quantum efficiency measurements showed a spectral response up to approximately 500 nm owing to the absorption by the few-atomic-layer MoS₂ film.     

Photoelectrochemical characterization of annealed cadmium selenide photoelectrode using sulphide–polysulphide electrolyte

Cadmium selenide films have been synthesized by dip method. Cadmium selenide acts as photoanode in photoelectrochemical (PEC) cells. The photoanode was annealed upto 473 K. The cell configuration is n-CdSe∣NaOH (1 M) +S (1 M) +Na₂S (1 M) ∣C_(graphite). Various performance parameters were examined with respect to annealed temperature. It is found that the fill factor and efficiency are maximum for photoelectrode annealed at 473 K. This is due to low resistance, high flat-band potential, maximum open-circuit voltage as well as maximum short-circuit current. The barrier height was examined from the temperature dependence of the reverse saturation current. The lighted ideality factor was found to be minimum for photoelectrode annealed at 473 K. A cell utilizing annealed photoelectrode showed a wider spectral response. The utility of this work is in improving the efficiency of PEC cells.     

Light intensity and temperature dependence on performance of a photoelectrochemical cells of ITO/TiO<Subscript>2</Subscript>/PVC-LiClO<Subscript>4</Subscript>/graphite

The photovoltaic characteristics of a photoelectrochemical cell of ITO/TiO₂/PVC-LiClO₄/graphite are reported. This paper is concerned with the influence of light intensity and temperature on short-circuit current density, J_sc and open-circuit voltage, V_oc of the device. The photoelectrochemical cell material was a screen-printed layer of titanium dioxide onto an ITO-covered glass substrate, which was used as a working electrode of the cell. The solid electrolyte was polivinylchloride-lithium perchlorate. The graphite film serves as a counter electrode of the cell. The current density–voltage characteristics of the device under an illumination of 20, 40, 60, 80 and 100 mW cm⁻² light from a tungsten halogen lamp were recorded at 40 °C as well as under an illumination of 100 mW cm⁻² at 30, 35, 40, 45 and 50 °C, respectively. It was found that the short-circuit current density, J_sc of the device increases with both light intensity and temperature. The J_sc obtained at 100 mW cm⁻² was 1.0 μAcm⁻² and that at 50 °C was 0.7 μAcm⁻².     

Effect of CdS modification on photoelectric properties of TiO2/PbS quantum dots bulk heterojunction

TiO₂/PbS(CdS) quantum dots (QDs) bulk heterojunction has been fabricated by successive ionic layer adsorption and reaction method via alternate deposition of PbS and CdS QDs. In comparison with TiO₂/PbS heterojunction, the incident photon to current conversion efficiency was increased almost 50% in the visible region. Meantime, the short-circuit current and open-circuit voltage were enhanced 200% and 35% respectively. The influence mechanism of CdS is related to reduction of trap state density at TiO₂/PbS interface and PbS QDs surface by the discussion of the dark current density–voltage curves, the transient photocurrent response curves and the electrochemical impedance spectra spectroscopy (EIS).     

Photoelectric properties of ZnO: In nanorods/SiO2/Si heterostructure assembled in aqueous solution

In-doped zinc oxide (ZnO:In) nanorods were grown onto SiO₂/n-Si substrate without catalyst in aqueous solution. The ZnO:In nanorods/SiO₂/n-Si heterostructure photovoltaic device was prepared. The structural and photoelectric properties of the as-grown ZnO:In nanorods were analyzed. ZnO:In nanorods had a strong and broad UV surface photovoltage response in the range of 300–400 nm, and the bands were identified. The photoelectric conversion properties of ZnO:In nanorods/SiO₂/n-Si heterostructure were investigated. ZnO:In/SiO₂/n-Si heterostructure showed a wide range photocurrent spectral response with high intensity in the UV and visible region. The rectifying behavior of this heterostructure was observed. Moreover, the device had a low turn-on voltage and a high breakdown voltage. Current–voltage characteristic was studied for the heterostructure, and the open-circuit voltage and short-circuit current were obtained. PACS 73.40.Lq; 85.35.Be; 81.16.Dn     

Influence of H2O/DEZ ratio on LPCVD ZnO:B films for application in a-Si:H/μc-Si:H tandem solar cells

In this study, boron doped zinc oxide (ZnO:B) films were prepared at different water to diethyl zinc (H₂O/DEZ) flow ratios from 0.6 to 1.4 by a low pressure chemical vapor deposition (LPCVD) technique. It is found that the morphology of ZnO:B films varies from small leaf-like to pyramidal surface structures with the increasing H₂O/DEZ flow ratio. The rough ZnO:B films deposited at a relatively H₂O/DEZ flow ratio such as 1.2 or 1.4 show a high haze value of up to 28 % at 600 nm and $\mathrm{a} (11\overline{2}0)$ preferential crystallographic orientation. All ZnO:B films were applied in hydrogenated amorphous silicon/microcrystalline silicon tandem solar cells (a-Si:H/μc-Si:H) as front electrodes. The efficiency of the solar cells increases with the increasing H₂O/DEZ flow ratio, which is attributed to a high spectral response mainly in the long-wavelength range and the consequent enhancement of short-circuit current. A high-efficiency a-Si:H/μc-Si:H tandem solar cell of 10 % was achieved. The H₂O/DEZ ratio is an important process parameter to tune the material properties of LPCVD ZnO:B films and the performances of corresponding silicon thin film solar cells.     

Effect of indium doping on photoelectrochemical properties of Cd0.9Zn0.1Se photosensitive films

Indium doped Cd_0.9Zn_0.1Se films have been synthesized by chemical bath deposition method. The deposited films act as photoanode in photoelectrochemical (PEC) cells. The varying concentration of indium from 0.01 to 1.0 mol% was used. The film thickness increases from 0.72 to 0.80 μm as doping concentration increases up to 0.1 mol%, thereafter it decreases. The cell configuration is n-Cd_0.9Zn_0.1Se:In|NaOH (1 M)+S (1 M)+Na₂S (1 M)|C_(graphite). The various performance parameters were examined with respect to doping concentration of indium. It is found that fill factor and efficiency is maximum for 0.1 mol% indium photosensitive films. This is due to low resistance, high flat band potential, maximum open circuit voltage as well as maximum short-circuit current. The barrier height was examined from the temperature dependence of the reverse saturation current. The lighted ideality factor was found to be minimum for 0.1 mol% indium photosensitive films. A cell utilizing doping photosensitive films showed a wider spectral response. The utility of this work is in improving efficiency of the PEC cell.     

一种印刷型薄膜太阳能电池p-n结调制技术

能带值为0.5~0.85 eV材料的稀缺是多结太阳能电池面临的一个主要挑战,本文使用非真空的机械化学法合成了能带值为0.83 eV的Cu₂SnS₃化合物,使用印刷技术将其制备成吸收层薄膜,并采用superstrate太阳能电池结构(Mo/Cu₂SnS₃/In₂S₃/TiO₂/FTO glass)对其光伏特性进行了研究.实验表明所制备的太阳能电池短路电流密度、开路电压、填充因子和转换效率分别为12.38 mA/cm²、320 mV、0.28和1.10%.此外,为更好地满足多结太阳能电池对电流匹配的需求,本文对所制备太阳能电池的Cu₂SnS₃/In₂S₃ p-n结进行了分析.通过在p-n结界面植入一层薄的疏松缓冲层,使调制后的太阳能电池短路电流密度从最初的12.38 mA/cm²增加到了23.15 mA/cm²,相应太阳能电池转换效率从1.1%增加到了1.92%.该p-n调制技术对印刷型薄膜太阳能电池具有重要借鉴意义.     

Influence of heat treatment on the electrophysical properties of thin films of copper-indium diselenide

An investigation of the structural, electrical, optical, and thermophysical properties is carried out on thin polycrystalline films of the ternary semiconductor CuInSe₂, which is potentially useful for fabricating solar cells. The thin films were obtained by thermal evaporation of CuInSe₂ and Se powder from two independent sources and by high-vacuum deposition in a closed cell (quasiequilibrium deposition). The influence of annealing in air on the parameters of the thin films is analyzed, and the dynamics of variation in the properties of the films are investigated as a function of the annealing time. Temperature dependences of the electrical conductivity, mobility, and thermal conductivity of CuInSe₂ thin films are given together with the spectral dependence of the short-circuit photocurrent of a photosensitive Au-CuInSe₂-Au structure. Zh. Tekh. Fiz. 67, 34–38 (March 1997)     

Comparison of the performances of dye-sensitized solar cells based on different TiO2 electrode nanostructures

This article reports on the performances of dye-sensitized solar cells based on three different working electrode structures, i.e., (i) sintered TiO₂ nanoparticles (20–40 nm diameters), (ii) ordered arrays of TiO₂ nanotubules (150 nm external diameters and 80 nm internal diameters), and (iii) ordered arrays of TiO₂ nanorods (150 nm diameters). Even though the highest short-circuit current density was achieved with systems based on TiO₂ nanotubules, the most efficient cells were those based on ordered arrays of TiO₂ nanorods. This is probably due to higher open-circuit photovoltage values attained with TiO₂ nanorods than with TiO₂ nanotubules. The nanorods are thicker than the nanotubules and therefore the injected electrons, stored in the trap states of the inner TiO₂ molecules, are shielded from recombination with holes in the redox electrolyte at open circuit. The high short-circuit photocurrent densities seen in the ordered TiO₂ systems can be explained by the fact that, as opposed to the sintered nanoparticles, the parallel and vertical orientation of the ordered nanostructures provide well-defined electrons percolation paths thus significantly reduce the diffusion distance and time constant.     

On the mechanism of current passage in metal/<Emphasis Type="Italic">p</Emphasis>-CuInSe<Subscript>2</Subscript> structures

Mechanisms of current passage and the temperature dependence of the current-voltage characteristics in Schottky diodes produced by vacuum evaporation of indium on p-CuInSe₂ single crystals are discussed. High values of the open-circuit voltage and short-circuit current in these surface-barrier diodes, as well as a high reproducibility of these parameters, suggest that such an inexpensive and rather simple technology is promising for efficient conversion of solar radiation.     

Temperature dependence of GaSb and AlGaSb solar cells

Sb-based alloys offer great potential for photovoltaic and thermophotovoltaic applications. In this paper, we study the performance of Al_xGa_1-xSb (x = 0, 0.15, and 0.50) single-junction solar cells over a temperature range of 25–250 °C. The dark current-voltage, one-sun current-voltage, and external quantum efficiency measurements were acquired at different temperatures. Correlations between experimental and numerical results are made to draw conclusions about the thermal behavior of the cells. It is shown that, while the bandgaps decrease linearly with temperature leading to the reduction of open-circuit voltages, the short-circuit current densities decrease with non-linear trends. The temperature-dependent dark current densities were extracted by fitting the dark current-voltage curves to single- and double-diode models to give an insight into the effect of intrinsic carrier concentration (n_i) on the cell performance. We find that the n_i has a significant impact on temperature-dependent cell performance. These findings could lay a groundwork for the future Sb-based photovoltaic systems that operate at high temperatures.     

Photovoltaic and pyroelectric effects in self-polarized ferroelectric <Emphasis Type="Italic">PZT</Emphasis>(25/75) films

The stationary photovoltaic effect in self-polarized Pb(Zr_0.25,Ti_0.75)O₃ films with a semitransparent top NiCr electrode was measured. The correlation between the pyroelectric response and short-circuit photocurrent was established. The effect of pre-polarization on the short-circuit photocurrent value is considered. It is assumed that upon film ageing, the abnormal photovoltaic effect degenerates into the barrier effect.     

Low-frequency noise in monodisperse platinum nanostructures near the percolation threshold

The percolation threshold p ₀ ≈ 0.6 is determined for monodisperse platinum nanostructures with 1.8-nm metallic particles deposited in a monolayer onto an insulating substrate through laser electrodispersion. It is shown that, in the “metallic” state (for p > p ₀), both the magnitude of the noise and its temperature dependence are close to those of pure metallic Pt layers. The frequency dependence of the normalized noise power spectral density is described by the relationship S _I /I ² ～ 1/f ^γ with the exponent γ close to unity. For current densities j ≥ 10⁷?10⁸ A/cm², the noise power spectral density S _I increases more rapidly with a further increase in the current as compared to I ² because of the current generating excess defects. For p < p ₀, the dependence of the conductivity σ on the temperature is adequately described by the standard relationship σ ～ exp[?(T ₀/T)^1/2]. The normalized noise power spectral density S _I /I ² exceeds the corresponding value for a quasi-metallic structure by many orders of magnitude. The noise power spectral density S _I is approximately proportional to the square of the current only for very low currents and increases steeply with a further increase in the current.     

Short-circuit current limiter utilizing a high-Tc superconductor

Experimental data are given on a prototype short-circuit current limiter utilizing a polycrystalline high-T _c superconductor of composition Y₁Ba₂Cu₃O_7−δ . The limiter comprises a seriesconnected dc circuit element immersed in liquid nitrogen. To improve the efficiency, a polycrystalline high-T _c superconductor having an S-shaped current-voltage characteristic is used as the current limiter. Zh. Tekh. Fiz. 68, 129–130 (October 1998)