High efficiency low temperature grown Cu(In,Ga)Se2 thin film solar cells on flexible substrates using NaF precursor layers

We report a total‐area efficiency of 15.9% for flexible Cu(In,Ga)Se₂ thin film solar cells on polyimide foil (cell area 0.95 cm²). The absorber layer was grown by a multi‐stage deposition process at a maximum nominal process temperature of 420°C. The Na was added via evaporation of a NaF layer prior to the absorber deposition leading to an enhanced V_oc and FF. Growth conditions and device characterization are described. Copyright © 2011 John Wiley & Sons, Ltd.     

磁控反应溅射直接生长绒面H化Ga掺杂ZnO-TCO薄膜及其特性研究

采用直流磁控溅射技术,在玻璃衬底上直接生长出了具有绒面结构的H化Ga掺杂ZnO(HGZO)薄膜。研究了H2流量对薄膜结构、表面形貌及光电特性的影响。实验表明,在溅射过程中引入H2明显改善HGZO薄膜电学性能,并且能够直接获得具有绒面结构的薄膜。在H2流量为2.0sccm时,所制备的HGZO薄膜具有特征尺寸约200nm的类金字塔状表面形貌,同时薄膜方阻为4.8Ω,电阻率达到8.77×10-4Ω.cm。H2的引入可以明显改善薄膜短波区域的光学透过,生长获得的HGZO薄膜可见光区域平均透过率优于85%,近红外区域波长到1 100nm时仍可达80%。为了进一步提高薄膜光散射能力和光学透过率,根据不同H2流量下HGZO薄膜性能的优点,提出了梯度H2技术生长HGZO薄膜;采用梯度H2工艺生长获得的HGZO薄膜长波区域透过率有了一定的提高,薄膜具有弹坑状表面形貌,并且其光散射能力有了明显提高。     

High quality baseline for high efficiency,Cu(In1−x,Gax)Se2 solar cells

We report on the progress that we have made in the quality of our baseline process for the production of high efficiency soda lime glass/Mo/Cu(In,Ga)Se₂ (CIGS)/CdS/i‐ZnO/ZnO:Al/MgF₂ solar cells. The enhancement of the average performance level has enabled us to reach conversion efficiencies of up to 19·3% (internal measurement). The new quality initiative uses process control, optical and electrical modelling, and the critical revision of all process steps as tools for the attainment of the 19% efficiency level. Our experiments show that the compositional process window for CIGS solar cells that have an efficiency of η ≈ 19% is very wide. Accordingly, we suggest that an efficiency of 19·0–19·5% is achievable in the following compositional process windows: 0·69 ≤ Cu/(Ga + In) ≤ 0·98 and 0·21 ≤ Ga/(Ga + In) ≤ 0·38. In addition, our results show that large CIGS grains are not a necessary requirement for high efficiencies up to 19%. These findings and the partly lacking ability to correlate certain aspects of our progress with experimental parameters lead us to the conclusion that there are still some important process variables undiscovered. From this conclusion and from the evaluation of the available data we infer that there is a potential for the enhancement of CIGS solar cell efficiencies beyond 20%. Copyright © 2007 John Wiley & Sons, Ltd.     

Cu2ZnSnSe4 thin film solar cells produced by selenisation of magnetron sputtered precursors

Polycrystalline thin films of Cu₂ZnSnSe₄ (CZTSe) were produced by selenisation of Cu(Zn,Sn) magnetron sputtered metallic precursors for solar cell applications. The p‐type CZTSe absorber films were found to crystallize in the stannite structure (a = 5·684 Å and c = 11·353 Å) with an electronic bandgap of 0·9 eV. Solar cells with the indium tin oxide structure (ITO)/ZnO/CdS/CZTSe/Mo were fabricated with device efficiencies up to 3·2% measured under standard AM1·5 illumination. Copyright © 2009 John Wiley & Sons, Ltd.     

柔性衬底硅基太阳电池ZAO透明导电膜的研究

采用孪生对靶直流磁控溅射的方法,在室温下制备了ZnO:Al(ZAO)薄膜材料,将其应用于柔性衬底非晶硅薄膜太阳电池的窗口电极。通过调整Ar气流量(1.67×10-7 m3/s～8.33×10-7 m3/s),优化了ZAO薄膜的结构、成份及光电性能。得到如下结论:理想的Ar气流量为3.33×10-7 m3/s,此时ZAO薄膜具有较高的晶化率和C轴择优取向,薄膜的霍尔电阻率达为4.26×10-4Ω.cm,载流子浓度达到1.8×1021cm-3,可见光波长范围内的光学透过率达到85%以上。将优化后的ZAO薄膜用于柔性衬底非晶硅薄膜太阳电池的窗口电极,转化效率达到了4.26%。     

Toward efficient Cu(In,Ga)Se2 solar cells prepared by reactive magnetron co‐sputtering from metallic targets in an Ar:H2Se atmosphere

In this paper, we show that a reactive co‐sputtering process using metallic CuGa and In targets; an Ar:H₂Se atmosphere is well suited for the deposition of photoactive Cu(In,Ga)Se₂ (CIGSe) absorber layers for thin‐film solar cells in a single process step. The achievement of single‐phase and well‐crystallized layers is thereby no major problem if a sufficiently high H₂Se content and substrate temperatures in the range of 400–500 °C are used. However, in order to achieve the desired Cu‐poor film stoichiometry, which is crucial for the device performance, it has to be considered already that, at moderate substrate temperatures in the range of 400–500 °C, indium has a strong tendency to re‐evaporate from the film surface if the film composition is Cu‐poor. If excess indium is supplied, this effect can lead to a self‐adjustment of the film composition. This allows a very wide process window in a one‐stage process concerning the supply ratio from the two targets of [Cu]/([In] + [Ga])_supply ≈ 0.35–0.8. However, the maximum efficiencies achievable with such a process are limited to 11.7% because an adequate Cu‐poor composition can only be achieved with significant Cu‐poor conditions, which allow only a low material quality. By using an improved process with an intermediate Cu‐rich composition and a final Cu‐poor stage, the absorber quality could be significantly improved; efficiencies of up to 14.3% have been achieved with CIGSe films prepared on Na‐doped Mo back contacts. Copyright © 2015 John Wiley & Sons, Ltd.     

The effect of Mo back contact ageing on Cu(In,Ga)Se2 thin‐film solar cells

In this work, we investigate the effect of ageing Mo‐coated substrates in a dry and N₂ flooded cabinet. The influence was studied by preparing Cu(In,Ga)Se₂ solar cells and by comparing the electrical performance with devices where the Mo layer was not aged. The measurements used for this study were current–voltage (J‐V), external quantum efficiency (EQE), secondary ion mass spectroscopy (SIMS) and capacitance–voltage (C‐V). It was concluded that devices prepared with the aged Mo layer have, in average, an increase of 0.8% in efficiency compared with devices that had a fresh Mo layer. Devices with aged Mo exhibited a nominal increase of 12.5 mV of open circuit voltage, a decrease of 1.1 mA/cm⁻² of short circuit current and a fill factor increase of 2.4%. Heat treatment of fresh Mo layers in oxygen atmosphere was also studied as an alternative to ageing and was shown to provide a similar effect to the aged device's performance. Copyright © 2013 John Wiley & Sons, Ltd.     

Properties of 19.2% efficiency ZnO/CdS/CuInGaSe2 thin‐film solar cells

We report the growth and characterization of record‐efficiency ZnO/CdS/CuInGaSe₂ thin‐film solar cells. Conversion efficiencies exceeding 19% have been achieved for the first time, and this result indicates that the 20% goal is within reach. Details of the experimental procedures are provided, and material and device characterization data are presented. Published in 2003 by John Wiley & Sons, Ltd.     

低温生长ITO薄膜及其在太阳电池中的应用

氧化铟锡(ITO)同时结合了可见光范围内高透过率和高电导率等特性,被广泛应用于Si基薄膜太阳电池中。本文侧重研究了采用反应热蒸发(RTE)技术低温(约160℃)生长ITO透明导电薄膜过程中不同Sn掺杂含量对薄膜微观结构以及光电性能的影响。实验结果表明,随着Sn掺杂含量的增加,ITO薄膜微观结构稍有变化,薄膜的电子迁移率呈现先增大后减小的趋势,薄膜的光学带隙一定程度上呈现展宽趋势;对于较高的Sn掺杂含量,在低温条件下电离杂质散射和中性杂质散射成为影响电子迁移率降低的重要因素。经过薄膜生长优化,较佳的Sn掺杂含量为6.0wt.%,ITO薄膜电阻率为3.74×10-4Ω·cm,电子迁移率为47cm2/Vs,载流子浓度为3.71×1020cm-3,且在380~900nm波长范围内的平均透过率约87%。将其应用于结构为SS/Ag/ZnO/nip aSiGe:H/nipa-Si:H/ITO/Al的n-i-p型a-Si:H/a-SiGe:H叠层太阳电池,取得的光电转化效率达10.51%(开路电压Voc=1.66V,短路电流密度Jsc=9.31mA/cm2,填充因子FF=0.68)。     

Na‐induced efficiency boost for Se‐deficient Cu(In,Ga)Se2 solar cells

Among different process routes for Cu(In,Ga)Se₂ (CIGS) solar cells, sufficient Se supply is commonly required to obtain high‐quality CIGS films. However, supplying extra Se increases the cost and the complexity. In this work, we demonstrate that extra Na incorporation can substantially increase efficiency of Se‐deficient CIGS solar cells, fabricated by sputtering from a quaternary CIGS target without extra Se supply, from 1.5% to 11.0%. The Se‐deficient CIGS device without extra NaF reveals a roll‐over I–V curve at room temperature as well as significantly reduced J_sc and fill factor at low temperatures. The electrical characteristics of Se‐deficient CIGS films are well explained and modeled by the low p‐type doping due to high density of compensating donors and the presence of deep defects possibly originating from the anti‐bonding levels of Se vacancies. The significant improvement after extra Na incorporation is attributable to the Na‐induced passivation of Se vacancies and the increased p‐type doping. Our result suggests that extra Na addition can effectively compensate the Se deficiency in CIGS films, which provides a valuable tuning knob for compositional tolerance of absorbers, especially for the Se‐deficient CIGS films. We believe that our findings can shine light on the development of novel CIGS processes, distinct from previous ones fabricated in Se‐rich atmosphere. Copyright © 2015 John Wiley & Sons, Ltd.     

Rapid annealing of reactively sputtered precursors for Cu2ZnSnS4 solar cells

Cu₂ZnSnS₄ (CZTS) is a promising thin‐film absorber material that presents some interesting challenges in fabrication when compared with Cu(In,Ga)Se₂. We introduce a two‐step process for fabrication of CZTS films, involving reactive sputtering of a Cu‐Zn‐Sn‐S precursor followed by rapid annealing. X‐ray diffraction and Raman measurements of the sputtered precursor suggest that it is in a disordered, metastable CZTS phase, similar to the high‐temperature cubic modification reported for CZTS. A few minutes of annealing at 550 °C are sufficient to produce crystalline CZTS films with grain sizes in the micrometer range. The first reported device using this approach has an AM1.5 efficiency of 4.6%, with J_sc and V_oc both appearing to be limited by interface recombination. Copyright © 2012 John Wiley & Sons, Ltd.     

Recent progress of high efficiency Si thin‐film solar cells in large area

Si thin‐film solar cells are suitable to the sunbelt region due to a low temperature coefficient and to building integrated photovoltaics owing to flexible size, easily controllable transmittance, and an aesthetic design. Nevertheless, the application is limited until now due to their low conversion efficiency. We have developed a triple junction cell (a‐Si:H/a‐SiGe:H/µc‐Si:H) providing efficient light utilization. For the high efficiency, we have focused on the smoothing of high haze TCO, a low absorption window layer, a low refractive index interlayer, uniformity control of the thickness and crystalline volume fraction in the microcrystalline silicon layer, and a low absorption back reflector. Through these activities, we have achieved a world record of 13.4% stabilized efficiency in the small size cell (1 cm²) and 10.5% stabilized efficiency in the large area module (1.1 × 1.3 m²), certificated by the National Renewable Energy Laboratory and Advanced Industrial Science and Technology, respectively. This result was presented in solar cell efficiency tables (Version 41). At this moment, we have increased a stabilized efficiency of 11.2% (Output power 160 W) in the large area module. We will report on the advanced materials in detail for high efficiency. Copyright © 2014 John Wiley & Sons, Ltd.     

偏压量子效率测试在薄膜太阳能电池特性分析中的应用

薄膜太阳能电池在不同偏压下的量子效率(QE)会呈现非常不一样的结果.对不同波长范围内偏压量子效率的分析可以研究薄膜太阳能电池窗口层区域杂质补偿情况、主结势垒高低、背势垒高度等,还可以得出耗尽区宽度以及少子扩散长度等重要参数.通过实验测量与理论分析,给出了薄膜太阳能电池耗尽区宽度(W)和少子扩散长度(Ln)与偏压量子效率的关系,提出了一种新的拟合耗尽区宽度(W)和少子扩散长度(Ln)的方法,探讨了偏压量子效率测试在薄膜太阳能电池特性分析中的应用.     

Improvement of hydrogenated amorphous silicon germanium thin film solar cells by different p-type contact layer

In this study, we report an appreciably increased efficiency from 6% up to 9.1% of hydrogenated amorphous silicon germanium (a-SiGe:H) thin film solar cells by using a combination of different p-doped window layers, such as boron doped hydrogenated amorphous silicon (p-a-Si:H), amorphous silicon oxide (p-a-SiO_x:H), microcrystalline silicon (p-µc-Si:H), and microcrystalline silicon oxide (p-µc-SiO_x:H). Optoelectronic properties and the role of these p-layers in the enhancement of a-SiGe:H cell efficiency were also examined and discussed. An improvement of 1.62 mA/cm² in the short-circuit current density (J_sc) is attributed to the higher band gap of p-type silicon oxide layers. In addition, an increase in open-circuit voltage (V_oc) by 150 mV and fill factor (FF) by 6.93% is ascribed to significantly improved front TCO/p-layer interface contact.     

Si基薄膜太阳电池绒面ZGO透明导电膜的研究

采用孪生对靶直流磁控溅射的方法在室温下制备高质量的Ga掺杂ZnO(ZGO)透明导电薄膜,用HCl腐蚀的方法获得满足光散射特性的绒面ZGO薄膜。制备的ZGO样品为具有六角纤锌矿结构的多晶膜,具有(002)方向的择优取向。腐蚀后,绒面ZGO薄膜的晶粒度减小,电阻率基本不变。在可见光范围内,绒面ZGO的反射率比平面ZGO的反射率下降了10%左右。将绒面ZGO薄膜应用于p-i-n型非晶Si薄膜太阳电池中,有效提高了太阳电池性能,使得电池的短路电流提高到17.79 mA/cm2,电池的转换效率增加到7.23%。     

Improving the performance of Sb2Se3 thin film solar cells over 4% by controlled addition of oxygen during film deposition

Sb₂Se₃ has attracted great research interest very recently as a promising absorber material for thin film photovoltaics due to its suitable bandgap, high absorption coefficient, and non‐toxic, low cost, and earth abundant nature. In this work, a significant efficiency improvement to 4.8% of superstrate cadmium sulfide (CdS)/Sb₂Se₃ solar cells is obtained by the controlled addition of oxygen during thermal evaporation of Sb₂Se₃ films. Systematic materials and device physics characterization reveal that oxygen addition during Sb₂Se₃ film evaporation significantly improves the CdS/Sb₂Se₃ heterojunction quality through effective passivation of interfacial defect states, resulting in a substantial enhancement in device circuit voltage and short circuit current density. The 4.8% device is the highest efficiency thus far reported for Sb₂Se₃ thin film solar cells. Copyright © 2015 John Wiley & Sons, Ltd.     

Highly transparent modulated surface textured front electrodes for high‐efficiency multijunction thin‐film silicon solar cells

To further increase the efficiency of multijunction thin‐film silicon (TF‐Si) solar cells, it is crucial for the front electrode to have a good transparency and conduction, to provide efficient light trapping for each subcell, and to ensure a suitable morphology for the growth of high‐quality silicon layers. Here, we present the implementation of highly transparent modulated surface textured (MST) front electrodes as light‐trapping structures in multijunction TF‐Si solar cells. The MST substrates comprise a micro‐textured glass, a thin layer of hydrogenated indium oxide (IOH), and a sub‐micron nano‐textured ZnO layer grown by low‐pressure chemical vapor deposition (LPCVD ZnO). The bilayer IOH/LPCVD ZnO stack guarantees efficient light in‐coupling and light trapping for the top amorphous silicon (a‐Si:H) solar cell while minimizing the parasitic absorption losses. The crater‐shaped micro‐textured glass provides both efficient light trapping in the red and infrared wavelength range and a suitable morphology for the growth of high‐quality nanocrystalline silicon (nc‐Si:H) layers. Thanks to the efficient light trapping for the individual subcells and suitable morphology for the growth of high‐quality silicon layers, multijunction solar cells deposited on MST substrates have a higher efficiency than those on single‐textured state‐of‐the‐art LPCVD ZnO substrates. Efficiencies of 14.8% (initial) and 12.5% (stable) have been achieved for a‐Si:H/nc‐Si:H tandem solar cells with the MST front electrode, surpassing efficiencies obtained on state‐of‐the‐art LPCVD ZnO, thereby highlighting the high potential of MST front electrodes for high‐efficiency multijunction solar cells. Copyright © 2015 John Wiley & Sons, Ltd.     

Non‐destructive optical analysis of band gap profile,crystalline phase,and grain size for Cu(In,Ga)Se2 solar cells deposited by 1‐stage, 2‐stage,and 3‐stage co‐evaporation

Cu(In,Ga)Se₂ (CIGS) thin films co‐evaporated by 1‐stage, 2‐stage, and 3‐stage processes have been studied by spectroscopic ellipsometry (SE). The disappearance of a Cu_2‐xSe optical signature, detected by real time SE during multistage CIGS, has enabled precise endpoint control. Band gap energies determined by SE as depth averages show little process variation for fixed [Ga]/([In] + [Ga]) atomic ratio, whereas their broadening parameters decrease with increasing number of stages, identifying successive grain size enhancements. Refined SE analysis has revealed band gap profiling only for 3‐stage CIGS. Solar cells incorporating these absorbers have yielded increased efficiencies in correlation with phase control, grain size, and band gap profiling. Copyright © 2013 John Wiley & Sons, Ltd.     

Fabrication of Cu(In,Ga)Se2 thin films by sputtering from a single quaternary chalcogenide target

Single‐layered Cu‐In‐Ga‐Se precursors were fabricated by one‐step sputtering of a single quaternary Cu(In,Ga)Se₂ (CIGS) chalcogenide target at room temperature, followed by post selenization using Se vapor obtained from elemental Se pellets. The morphological and structural properties of both as‐deposited and selenized films were characterized by X‐ray diffraction (XRD), Raman spectroscope and scanning electron microscope (SEM). The precursor films exhibited a chalcopyrite structure with a preferential orientation in the (112) direction. The post‐selenization process at high‐temperature significantly improved the quality of the chalcopyrite CIGS. The CIGS layers after post‐selenization were used to fabricate solar cells. The solar cell had an open‐circuit voltage Voc of 0.422 V, a short‐circuit current density J = 24.75 mA, a fill factor of 53.29%, and an efficiency of 7.95%. Copyright © 2010 John Wiley & Sons, Ltd.     

面向高效单结GaInP太阳电池的介质复合纳米结构的仿真研究

以实现宽谱减反介质复合纳米结构表面的高 效单结GaInP太阳电池为目标,利用严格耦合波分析理论, 仿真研究了该电池表面的介质复合纳米结构对太阳电池宽谱减反、归一化吸收、最大化理想 效率的影响。该介质复 合纳米结构从上往下依次为SiO₂纳米锥、SiO₂介质层和SiNx介质层,通过对SiO₂纳米锥占空比、深宽比以及对SiO₂和SiNx介质层厚度等参数的系列仿真最终优化出适用于单结Ga InP电池的表面结构。结果表明:当SiO₂纳米锥底部 直径D=550nm、高度H=650 nm、SiN x介质层厚度为60 nm时电池具有最高的 最大化理想转换效率为28.58%。上述结果为后期实验以及该类电池 实现规模化生产奠定了基础。