Investigation of Cu2ZnSnS4 solar cell buffer layer fabricated via spray pyrolysis

Copper zinc tin sulfide solar cells were fabricated by using spray pyrolysis from a window layer to an absorber layer. ZnS and In₂S₃ buffer layers were deposited on the TiO₂ layer, and the photovoltaic characteristics were investigated. The ZnS buffer demonstrated a poor photovoltaic performance because of its poor surface coverage and micro-cracks at fluorine-doped tin oxide/TiO₂ layers. The In₂S₃ buffer layer sprayed at low temperature (<360 °C) showed a large difference between photo and dark currents beyond the open-circuit voltage (V_OC). When the spraying temperature exceeded 390 °C, the devices showed high dark leakage currents at reverse biases because of the high conductivity of the buffer layer, resulting in decreased V_OC and short-circuit current density (J_SC). The optimum temperature for spraying In₂S₃ is 360 °C, and the best performing device showed 410 mV, 30.4 mA/cm², 35.3%, and 4.4% of V_OC, J_SC, fill factor, and efficiency, respectively.     

Enhanced photovoltaic performance of solution-processed Sb2Se3 thin film solar cells by optimizing device structure

Thin-film solar cells have attracted worldwide attention due to their high efficiency and low cost. Antimony selenide (Sb₂Se₃) is a promising light absorption material candidate for thin-film solar cells due to its suitable band gap, abundance, low toxicity, and high chemical stability. Herein, we fabricate an Sb₂Se₃ thin film solar cell using a simple hydrazine solution process. By controlling the thickness of the photoactive layer and inserting a poly(3-hexylthiophene) hole-transporting layer, an Sb₂Se₃ solar cell with a power conversion efficiency of 2.45% was achieved.     

Optimization of the CIGS based thin film solar cells: Numerical simulation and analysis

Chalcopyrite Cu(In,Ga)Se (CIGS) is a very promising material for thin film photovoltaics and offers a number of interesting advantages compared to the bulk silicon devices. CIGS absorbers today have a typical thickness of about 1–2 μm. However, on the way toward mass production, it will be necessary to reduce the thickness even further. This paper indicates a numerical study to optimization of CIGS based thin film solar cells. An optimum value of the thickness of this structure has been calculated and it is shown that by optimizing the thickness of the cell efficiency has been increases and cost of production can be reduces. Numerical optimizations have been done by adjusting parameters such as the combination of band gap and mismatch as well as the specific structure of the cell. It is shown that by optimization of the considered structure, open circuit voltage increases and an improvement of conversion efficiency has been observed in comparison to the conventional CIGS system. Capacitance–voltage characteristics and depletion region width versus applied voltage for optimized cell and typical cell has been calculated which simulation results predict that by reducing cell layers in the optimized cell structure, there is no drastically changes in depletion layer profile versus applied voltage. From the simulation results it was found that by optimization of the considered structure, optimized value of CIGS and transparent conductive oxide thickness are 0.3 μm and 20 nm and also an improvement of conversion efficiency has been observed in comparison to the conventional CIGS which cell efficiency increases from 17.65 % to 20.34%, respectively.     

Cu(In,Ga)Se2 thin film solar cells from nanoparticle precursors

A non-vacuum process for Cu(In,Ga)Se₂ (CIGS) thin film solar cells from nanoparticle precursors was described in this work. CIGS nanoparticle precursors was prepared by a low temperature colloidal route by reacting the starting materials (CuI, InI₃, GaI₃ and Na₂Se) in organic solvents, by which fine CIGS nanoparticles of about 15 nm in diameter were obtained. The nanoparticle precursors were then deposited onto Mo/glass substrate by the doctor blade technique. After heat treating the CIGS/Mo/glass layers in Se gas atmosphere, a complete solar cell structure was fabricated by depositing the other layers including CdS buffer layer, ZnO window layer and Al electrodes by conventional methods. The resultant solar cell showed a conversion efficiency of 0.5%.     

Cu(In,Ga)Se2太阳能电池快速热退火效应

利用光致发光（PL）分析快速热退火对Cu(In,Ga)Se2 (CIGS)电池的影响,研究退火对薄膜缺陷的影响。Cu(In,Ga)Se2电池的PL谱中总共有 7个峰,即2个可见波段峰和5个红外波段峰。退火温度较低,可减少薄膜体内缺陷,提高载流子浓度,改善薄膜质量;退火温度过高,则会引起正常格点处元素扩散,元素化学计量比改变,体内缺陷增加,吸收层带隙降低,反而会对CIGS薄膜造成破坏。     

Cu(In,Ga)Se2太阳能电池快速热退火效应

利用光致发光（PL）分析快速热退火对Cu(In,Ga)Se2 (CIGS)电池的影响,研究退火对薄膜缺陷的影响。Cu(In,Ga)Se2电池的PL谱中总共有 7个峰,即2个可见波段峰和5个红外波段峰。退火温度较低,可减少薄膜体内缺陷,提高载流子浓度,改善薄膜质量;退火温度过高,则会引起正常格点处元素扩散,元素化学计量比改变,体内缺陷增加,吸收层带隙降低,反而会对CIGS薄膜造成破坏。     

Epitaxial Cu(In,Ga)S2 thin film solar cells

Epitaxial layers of the quaternary compound Cu(In,Ga)S₂ and the ternary compound CuInS₂ were grown on Si(111) substrates via Molecular Beam Epitaxy. The layers were investigated for their morphological and structural properties using Rutherford backscattering spectroscopy, atomic force microscopy, reflection high-energy electron diffraction and X-Ray diffraction. Furthermore, complete solar cell devices were processed from these layers and their photovoltaic properties were investigated by means of I(U)-curves under illumination. Thus, efficiencies up to η=3.2% were achieved. The comparatively low performance of the solar cell devices is attributed to certain heterogeneities of the samples as a result of the growth process.     

para-Sexiphenyl thin film growth on Cu(1 1 0) and Cu(1 1 0)-(2 × 1)O surfaces

We present a reflectance difference spectroscopy (RDS) study of para-sexiphenyl (p-6P) thin film growth on Cu(1 1 0) and Cu(1 1 0)-(2 × 1)O substrates. The RDS spectra show pronounced anisotropies for p-6P films formed on both substrates at room temperature, demonstrating that the molecules are uniaxially aligned within the films. Based on the RD spectra and the evolution of the optical transitions with p-6P coverage the growth mode on both substrates could be identified. From the dominating RDS feature, assigned to the lowest energy HOMO-LUMO transition, the orientation of the molecular chain can be determined. On Cu(1 1 0), the p-6P molecular chains align in the direction, i.e., along the Cu atomic rows, whereas on the Cu(1 1 0)-(2 × 1)O surface, the molecules are oriented in the orthogonal [0 0 1] direction, i.e., along the “added” Cu-O rows of the Cu(1 1 0)-(2 × 1)O surface. The energetic position and line shape of the main RDS feature differs for the two substrates and varies with p-6P coverage. This fine structure is discussed in terms of different molecular conformations, adlayer structure and vibronic replicas.     

CdSxTe1-x多晶薄膜的制备与性质研究

采用真空共蒸发方法制备了CdSxTe1 -x 多晶薄膜 ,并用原子力显微镜、x射线衍射和光学透过率谱等研究了CdSxTe1 -x多晶薄膜的结构和性质 .结果表明 :薄膜均匀、致密、无微孔 ,当x≥ 0 5时为n型半导体 ,x <0 5时为p型半导体 .CdSxTe1 -x多晶薄膜的光学能隙随x变化 .结合薄膜的晶格常数和光学能隙得到了薄膜发生相变的组分 ,当x<0 2 5时CdSxTe1 -x 多晶薄膜为立方相 ,当x >0 2 5时为六方结构 .退火后结构没有改变 ,能隙减小 .提出了用CdSxTe1 -x多晶薄膜作为缓冲层的新型结构太阳电池 .     

Enhancement of output performance of Cu2ZnSnS4 thin film solar cells—A numerical simulation approach and comparison to experiments

The formation of stable, low resistance and nonrectifying contacts to Cu₂ZnSnS₄ (CZTS) thin film photovoltaic material are the major and critical challenges associated with its effect over the output performance of fabricated solar cells. The solution of continuity equation in one dimension for a soda lime glass substrates (SLG) |Mo | CZTS | CdS | ZnO:Al cell structure is considered in the simulation of its current–voltage characteristics that is governed by the back contact material, acceptor concentration as well as thickness of the CZTS layer. Our primary simulation shows a 6.44% efficiency of the CZTS solar cell which is comparable to reported experimental data if these parameters are not optimized. However, by optimizing them a simulated conversion efficiency as high as 13.41% (V_oc=1.002 V, J_sc=19.31 mA/cm², fill factor (FF)=69.35%) could be achievable. The solar cell with a back contact metal work function of 5.5 eV, an absorber layer's thickness of 2.68 μm and an acceptor concentration of 5×10¹⁶ cm⁻³ were optimum. The presented optimization is ideal and subject to experimental verification with a precise control of the process parameters along with reduced surface as well as bulk recombination, secondary phases and thermalization losses.     

Cu元素对Cu(In,Ga)Se_2薄膜及太阳电池的影响

Cu元素成分对Cu(In,Ga)Se2(简称CIGS)薄膜材料的电学性质及其电池器件性能有很重要的影响.本文利用蒸发法制备了贫Cu和富Cu的CIGS吸收层(0.7Cu/(Ga+In)1.15)及相应的电池器件.扫描电镜和Hall测试发现,富Cu材料的结构特性(晶粒大、结晶状态好)和电学特性(电阻率低、迁移率高等)优于贫Cu材料,而性能测试表明贫Cu器件的效率优于富Cu器件.变温性能测试分析表明,贫Cu器件的主要复合路径是体复合,激活能与CIGS禁带宽度相当;富Cu器件的主要复合路径是界面复合,其激活能远小于CIGS禁带宽度,这大大降低了开路电压Voc,从而降低了电池效率.最后利用蒸发三步法制备了体材料稍富Cu表面贫Cu的CIGS吸收层,降低了短路电流和开路电压的损失,获得了超过15%的电池效率.     

CdTe太阳电池前电极SnO2:F/SnO2复合薄膜性能分析

减薄CdS窗口层是提高CdS/CdTe太阳电池转换效率的有效途径之一,减薄窗口层会对器件造成不利的影响,因此在减薄了的窗口层与前电极之间引入过渡层非常必要.利用反应磁控溅射法在前电极SnO₂:F薄膜衬底上制备未掺杂的SnO₂薄膜形成过渡层,并将其在N₂/O₂=4 ∶1,550 ℃环境进行了30 min热处理,利用原子力显微镜、X射线衍射仪、紫外分光光度计对复合薄膜热处理前后的形貌、结构、光学性能进行了表征,同时分析了复     

Structural and optical properties of thermally evaporated 2-(2,3-dihydro-1,5-dimethyl-3-oxo-2-phenyl-1H-pyrazol-4-ylimino)-2-(4-nitrophenyl)acetonitrile thin films

The structural and optical properties of as-deposited and γ-rays irradiated 2-(2,3-dihydro-1,5dimethyl-3-oxo-2-phenyl-1H-pyrazol-4-ylimino)-2-(4-nitrophenyl)acetonitrile (DOPNA) thin films have been reported. The structural properties of as-deposited and γ-rays irradiated DOPNA thin films are characterized by Fourier transformation infrared, X-ray diffraction and transmission electron microscope techniques. The transmittance, T(λ), and reflectance, R(λ), are measured at the normal incidence of light by a double beam spectrophotometer in the wavelength range 200-2200 nm. The refractive and absorption indices have been calculated. The dispersion parameters such as dispersion energy, oscillator energy and dielectric constant at high frequency are evaluated. The data of the absorption coefficient are analyzed in order to determine the type of inter-band electronic transitions and the optical band gap of the films. Other optical absorption parameters, namely, the extinction molar coefficient, oscillator strength and the electric dipole strength, are also calculated.     

Improvement of organic solar cells by flexible substrate and ITO surface treatments

In this paper, surface treatments on polyethylene terephthalate with polymeric hard coating (PET-HC) substrates are described. The effect of the contact angle on the treatment is first investigated. It has been observed that detergent is quite effective in removing organic contamination on the flexible PET-HC substrates. Next, using a DC-reactive magnetron sputter, indium tin oxide (ITO) thin films of 90 nm are grown on a substrate treated by detergent. Then, various ITO surface treatments are made for improving the performance of the finally developed organic solar cells with structure Al/P3HT:PCBM/PEDOT:PSS/ITO/PET. It is found that the parameters of the ITO including resistivity, carrier concentration, transmittance, surface morphology, and work function depended on the surface treatments and significantly influence the solar cell performance. With the optimal conditions for detergent treatment on flexible PET substrates, the ITO film with a resistivity of 5.6 × 10⁻⁴ Ω cm and average optical transmittance of 84.1% in the visible region are obtained. The optimal ITO surface treated by detergent for 5 min and then by UV ozone for 20 min exhibits the best WF value of 5.22 eV. This improves about 8.30% in the WF compared with that of the untreated ITO film. In the case of optimal treatment with the organic photovoltaic device, meanwhile, 36.6% enhancement in short circuit current density (J_sc) and 92.7% enhancement in conversion efficiency (η) over the untreated solar cell are obtained.     

Effects of heavy alkali elements in Cu(In,Ga)Se2 solar cells with efficiencies up to 22.6%

We report on the use and effect of the alkali elements rubidium and caesium in the place of sodium and potassium in the alkali post deposition treatment (PDT) as applied to Cu(In,Ga)Se₂ (CIGS) solar cell absorbers. In order to study the effects of the different alkali elements, we have produced a large number of CIGS solar cells with high efficiencies resulting in a good experimental resolution to detect even small differences in performance. We examine the electrical device parameters of these fully functional devices and observe a positive trend in the I –V parameters when moving from devices without PDT to KF‐, RbF‐, and eventually to CsF‐PDT. A diode analysis reveals an improved diode quality for cells treat‐ed with heavier alkalis. Furthermore, secondary ion mass spectrometry (SIMS) measurements reveal a competitive mechanism induced within the class of alkali elements in the CIGS absorber induced by the alkali post deposition treatment. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Stage2沉积速率对低温生长CIGS薄膜特性及器件的影响

研究了三步法第二步沉积速率对低温生长Cu(In,Ga)Se₂薄膜结构、 电学特性和器件特性的影响. 通过改变第二步沉积速率发现, 提高沉积速率可以显著促进薄膜晶粒生长, 提高晶粒紧凑程度降低晶界复合, 同时有效改善两相分离现象, 提高电池的开路电压和短路电流, 有助于Cu(In,Ga)Se₂电池光电转换效率的提高. 但同时研究表明, 随着第二步沉积速率的增加, 会促进暂态Cu_2-xSe晶粒的生长, 引起Cu(In,Ga)Se₂薄膜表面粗糙度增大, 并阻碍Na向Cu(In,Ga)Se₂薄膜表面的扩散, 造成施主缺陷钝化效应降低, 薄膜载流子浓度下降和电阻率升高, 且过高的沉积速率会引起电池内部复合增加并产生分流路径, 造成开路电压下降进而引起电池效率恶化. 最终, 通过最佳化第二步沉积速率, 在衬底温度为420℃时, 得到最高转换效率为11.24%的Cu(In,Ga)Se₂薄膜太阳电池.     

Efficiency enhancement of Cu(In,Ga)Se2 thin‐film solar cells by a post‐deposition treatment with potassium fluoride

Alkali‐free Cu(In,Ga)Se₂(CIGS) absorbers grown on Mo‐coated alumina (Al₂O₃) substrates were doped with potassium (K) after CIGS growth by a potassium fluoride (KF) post‐deposition treatment (PDT). The addition of K to the absorber leads to a strong increase in cell efficiency from 10.0% for the K‐free cell to 14.2% for the K‐doped cell, mainly driven by an increase in the open‐circuit voltage V_oc and the fill factor FF, and to an increase in the net charge carrier density. Hence K doping by KF‐PDT is comparable to doping with Na.

     

Optoelectrical improvement of ultra‐thin Cu(In,Ga)Se2 solar cells through microstructured MgF2 and Al2O3 back contact passivation layer

Decreasing the absorber layer thickness of thin‐film solar cells can be an effective solution for cost reduction of photovoltaic electricity generation. Unfortunately, this reduction leads to detrimental effects such as incomplete photon absorption and increased charge carrier recombination at the rear electrode. To tackle these losses in ultra‐thin 0.5 µm Cu(In,Ga)Se₂ (CIGS) solar cells, we developed different passivation structures made of MgF₂ and Al₂O₃ at the molybdenum–CIGS interface, leading to localized back contacts. The influence of the distance between those contacts on the cell performance was studied by varying the periodicity of the applied 1D patterns from 6 μm to 30 μm. Thus, an increase in performance was measured for microstructured layers with a periodicity of up to 12 µm. More precisely, a MgF₂ layer yielded an increase in power conversion efficiency (PCE) of up to 9%_rel compared to an unpassivated cell design, and a passivation layer comprising Al₂O₃ led to up to a 5%_rel increase in PCE. The gains were primarily attributed to an increased reflectivity of the back contact, while the formation of a negative backside field in the case of Al₂O₃ might have contributed to this increase by preventing electrons from recombining at the backside interface. Our findings indicate a high lateral conductivity for holes inside the multicrystalline CIGS compound over few tens of micrometres, which allows an independent design of future back contacts and light‐trapping schemes.

False‐colour scanning electron microscopy cross‐section picture of a passivated solar cell, with the front contact layers coloured in green, the 0.5 µm CIGS absorber in dark red, the MgF₂ passivation layer in blue, and the Mo back contact in grey.