Morphology controlled open circuit voltage in polymer solar cells

We report a strong dependence of open circuit voltage on the altered morphology of block copolymer (P3HT‐b ‐PPerAcr) based solar cells. The open circuit voltage increases dramatically by about 300 mV by increasing the amount of acceptor homopolymer within the block copolymer/homopolymer blends. The change in open circuit voltage is found to be in correlation with the enrichment of acceptor moiety at the film surface as identified by Atomic force microscopy (AFM) and X‐ray photoelectron spectroscopy (XPS). Based on this fact, an additional increase in open circuit voltage to its maximum values is achieved by introducing an acceptor buffer layer at the cathode interface. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nanoimprint texturing of transparent flexible substrates for improved light management in thin‐film solar cells

We present a nanoimprint based approach to achieve efficient light management for solar cells on low temperature transparent polymer films. These films are particularly low‐priced, though sensitive to temperature, and therefore limiting the range of deposition temperatures of subsequent solar cell layers. By using nanoimprint technology, we successfully replicated optimized light trapping textures of etched high temperature ZnO:Al on a low temperature PET film without deterioration of optical properties of the substrate. The imprint‐textured PET substrates show excellent light scattering properties and lead to significantly improved incoupling and trapping of light in the solar cell, resulting in a current density of 12.9 mA/cm², similar to that on a glass substrate. An overall efficiency of 6.9% was achieved for a flexible thin‐film silicon solar cell on low cost PET substrate. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Efficient nanocoax‐based solar cells

The power conversion efficiency of most thin film solar cells is compromised by competing optical and electronic constraints, wherein a cell must be thick enough to collect light yet thin enough to efficiently extract current. Here, we introduce a nanoscale solar architecture inspired by a well‐known radio technology concept, the coaxial cable, that naturally resolves this “thick–thin” conundrum. Optically thick and elec‐ tronically thin amorphous silicon “nanocoax” cells are in the range of 8% efficiency, higher than any nanostructured thin film solar cell to date. Moreover, the thin nature of the cells reduces the Staebler–Wronski light‐induced degradation effect, a major problem with conventional solar cells of this type. This nanocoax represents a new platform for low cost, high efficiency solar power. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Stability issues of the next generation solar cells

Polymer, perovskite, and dye‐sensitized solar cells (DSSCs) are promising technologies for next generation low cost photovoltaic cells. Among these, perovskite solar cells are the newest technology and have the highest efficiency, while DSSCs are closest to commercialization with several companies producing the DSSC materials and modules and existing DSSC installations. However, all three types of solar cells share a concern about lifetime and stability. For each type of devices, there are specific concerns and degradation mechanisms, and all of the devices require encapsulation and exhibit varying degrees of sensitivity to moisture, oxygen, elevated temperature and UV illumination depending on the device structure and materials used. We are discussing the stability and lifetime for each type of cells and future outlook of these technologies. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

制膜工艺对聚合物太阳电池性能影响的研究

用渡越时间法（TOF）分别测试了采用旋涂和滴涂方法制备的poly［2-methoxy-5-（2′-ethylhexyloxy）-1,4- phenylenevinylene］（MEH-PPV）薄膜的空穴迁移率,用原子力显微镜对这两种方法制备的薄膜表面形貌进行了研究.结果表明使用滴涂法有利于聚合物形成有序薄膜结构,能有效提高空穴迁移率.用滴涂法制备的基于MEH-PPV：phenyl C61- butyric acid methyl ester（PCBM）共混薄膜的太阳电池,对比用旋涂法制备的太阳电池,其能量 关键词： 太阳电池 聚合物 迁移率     

Very thin,highly‐conductive ZnO:Al front electrode on textured glass as substrate for thin‐film silicon solar cells

A very thin (250 nm), highly conductive (annealed), non‐texturized DC‐sputtered aluminum‐doped zinc oxide layer (ZnO:Al) deposited on a textured glass is used as substrate for thin‐film silicon solar cells. Compared to the classical approach, where wet‐chemically texturized ZnO:Al on planar glass is used, this approach allows a reduction in the as‐deposited ZnO:Al thickness of almost 70% while at the same time, thanks to the good light trapping capability of the glass texture the efficiency of the cells was maintained at the high level of 10.9%.

     

19.4%‐efficient large‐area fully screen‐printed silicon solar cells

We demonstrate industrially feasible large‐area solar cells with passivated homogeneous emitter and rear achieving energy conversion efficiencies of up to 19.4% on 125 × 125 mm² p‐type 2–3 Ω cm boron‐doped Czochralski silicon wafers. Front and rear metal contacts are fabricated by screen‐printing of silver and aluminum paste and firing in a conventional belt furnace. We implement two different dielectric rear surface passivation stacks: (i) a thermally grown silicon dioxide/silicon nitride stack and (ii) an atomic‐layer‐deposited aluminum oxide/silicon nitride stack. The dielectrics at the rear result in a decreased surface recombination velocity of S_rear = 70 cm/s and 80 cm/s, and an increased internal IR reflectance of up to 91% corresponding to an improved J_sc of up to 38.9 mA/cm² and V_oc of up to 664 mV. We observe an increase in cell efficiency of 0.8% absolute for the cells compared to 18.6% efficient reference solar cells featuring a full‐area aluminum back surface field. To our knowledge, the energy conversion efficiency of 19.4% is the best value reported so far for large area screen‐printed solar cells. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Hybrid polymer/inorganic nanoparticle blended ternary solar cells

Hybrid polymer/inorganic nanoparticle blended ternary solar cells are reported. These solar cells have an active layer consisting of PbS colloidal quantum dots (CQDs), poly (3‐hexylthiophene) (P3HT), and [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM). Power conversion efficiency (PCE) was improved by incorporating PbS CQDs in the active layer of P3HT:PCBM‐based organic solar cells. As the concentration of PbS CQDs in the hybrid solar cells was increased, PCE was also increased. This improvement resulted from improved charge transfer and also extended light absorption into the near‐infrared. The PCE of the hybrid solar cells was 47% higher than that for reference organic solar cells on average under air mass 1.5 global illumination. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Enhanced rear‐side reflection and firing‐stable surface passivation of silicon solar cells with capping polymer films

Low refractive index polymer materials have been investigated with a view to form the back surface mirror of advanced silicon solar cells. SiO_x:H or AlO_y SiO_x:H polymer films were spun on top of an ultra‐thin (<10 nm) atomic‐layer‐deposited (ALD) Al₂O₃ layer, itself deposited on low‐resistivity (1 Ω cm) p‐type crystalline silicon wafers. These double‐layer stacks were compared to both ALD Al₂O₃ single layers and ALD Al₂O₃/plasma‐enhanced chemical vapour deposited (PECVD) SiN_x stacks, in terms of surface passivation, firing stability and rear‐side reflection. Very low surface recombination velocity (SRV) values approaching 3 cm/s were achieved with ALD Al₂O₃ layers in the 4–8 nm range. Whilst the surface passivation of the single ALD Al₂O₃ layer is maintained after a standard firing step typical of screen printing metallisation, a harsher firing regime revealed an enhanced thermal stability of the ALD Al₂O₃/SiO_x:H and ALD Al₂O₃/AlO_y SiO_x:H stacks. Using simple two‐dimensional optical modelling of rear‐side reflection it is shown that the low refractive index exhibited by SiO_x:H and AlO_y SiO_x:H results in superior optical performance as compared to PECVD SiN_x, with gains in photogenerated current of ～0.125 mA/cm² at a capping thickness of 100 nm. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

柔性衬底非晶硅薄膜太阳电池界面处理的研究

通过实验和模拟计算对比分析了i/p界面过渡层对太阳电池性能的影响．结合具体实验工艺参数,模拟计算了不同带隙和缺陷态密度的过渡层对太阳电池的影响,同时结合实验情况重现了宽带隙高缺陷态密度过渡层对太阳电池的损伤,为实验结果提供了理论依据．通过优化调整i/p界面过渡层的制备方法得到了转换效率为7.09%的聚酰亚胺衬底非晶硅薄膜太阳电池． 关键词： 柔性衬底 太阳电池 AMPS 模拟计算     

Effects of photo‐induced defects on the performance of PBDTTT‐C/PC70BM solar cells

In this work, the effects of photo‐induced defects on polymer solar cells (PSCs) based on the blends of poly (4,8‐bis‐alkyloxybenzo (1,2‐b:4,5‐b′) dithiophene‐2,6‐diyl‐alt‐(alkyl thieno(3,4‐b) thiophene‐2‐carboxylate)‐2,6‐diyl) (PBDTTT‐C) and [6,6]‐phenyl C₇₀‐butyric acid methyl ester (PC₇₀BM) are investigated. In addition to conventional PSC characterization approaches, the capacitance–voltage (C–V) response and the ideality factor are used to analyze the changes in the built‐in potential and defect‐induced recombination at the internal donor/acceptor interface and the electrode interfaces in illuminated PSCs. The results show that the dominant trap states increase with increasing illumination time, which indicates that photo‐induced defects play an important role in the photodegradation of inverted PSCs. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Micro‐photoluminescence spectroscopy on heavily‐doped layers of silicon solar cells

We report and explain the photoluminescence spectra emitted from silicon solar cells with heavily‐doped layers at the surface. A micro‐photoluminescence spectroscopy system is employed to investigate the total spectrum emitted from both the heavily‐doped layer and the silicon substrate with micron‐scale spatial resolution. The two regions of the device give rise to separate photoluminescence peaks, due to band‐gap narrowing effects in the highly‐doped layer. Two key parameters, the absorption depth of the excitation wavelength, and the sample temperature, are shown to be critical to reveal the separate signatures from the two regions. Finally, this technique is applied to locally diffused and laser‐doped regions on silicon solar cell pre‐cursors, demonstrating the potential value of this micron‐scale technique in studying and optimizing locally doped regions. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Theory study on the properties of thiadiazole polymer donors for organic solar cells

In this work, the properties of [1,2,5] thiadiazolo [3,4‐c] pyridine ‐alt‐cyclopenta [2,1‐b:3,4‐b′] dithiophene (PT‐CDT) and [1,2,5] thiadiazolo [3,4‐c] pyridine‐6‐carbonitrile‐alt‐cyclopenta [2,1‐b:3,4‐b′] dithiophene (PCNT‐CDT) as donors were investigated by means of Density Functional Theory. The electronic properties and optical absorption properties were discussed, and hole‐transfer properties of donors were studied by Marcus electron transfer theory. The results indicate that the linear structure of PCNT‐CDT and PT‐CDT is more stable than the spiral structure of PCNT‐CDT and PT‐CDT; the absorption peak in visible region of PCNT‐CDT is stronger and wider, and the absorption spectrum is more matchable to solar spectrum than PT‐CDT, while the maximum absorption wavelength of PCNT‐CDT has an obvious red shift; the two designed materials show strong intramolecular and intermolecular charge transfer properties; PCNT‐CDT owns a large open‐circuit voltage and low reorganization energy, as well as high hole mobility. Therefore, the newly designed PCNT‐CDT can be a potential donor material of organic solar cell. Copyright © 2013 John Wiley & Sons, Ltd.     

Large‐area p‐type HIP‐MWT silicon solar cells with screen printed contacts exceeding 20% efficiency

We present metal wrap through (MWT) silicon solar cells with passivated surfaces based on a simplified device structure. This so‐called HIP‐MWT structure (high‐performance metal wrap through) does not exhibit an emitter on the rear side and therefore simplifies processing. The confirmed peak efficiency of the fabricated solar cells with an edge length of 125 mm, screen printed contacts and solder pads is 20.2%. To our knowledge, this is the highest value reported for large‐area p‐type silicon solar cells to date.

     

Potential‐induced optimization of ultra‐thin rear surface passivated CIGS solar cells

Ultra‐thin Cu(In,Ga)Se₂ (CIGS) solar cells with an Al₂O₃ rear surface passivation layer between the rear contact and absorber layer frequently show a “roll‐over” effect in the J–V curve, lowering the open circuit voltage (V_OC), short circuit current (J_SC) and fill factor (FF), similar to what is observed for Na‐deficient devices. Since Al₂O₃ is a well‐known barrier for Na, this behaviour can indeed be interpreted as due to lack of Na in the CIGS absorber layer. In this work, applying an electric field between the backside of the soda lime glass (SLG) substrate and the SLG/rear‐contact interface is investi‐gated as potential treatment for such Na‐deficient rear surface passivated CIGS solar cells. First, an electrical field of +50 V is applied at 85 °C, which increases the Na concentration in the CIGS absorber layer and the CdS buffer layer as measured by glow discharge optical emission spectroscopy (GDOES). Subsequently, the field polarity is reversed and part of the previously added Na is removed. This way, the J –V curve roll‐over related to Na deficiency disappears and the V_OC (+25 mV), J_SC(+2.3 mA/cm²) and FF (+13.5% absolute) of the rear surface passivated CIGS solar cells are optimized. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

ZnO电子传输层对于反型结构聚合物太阳电池光浴效应的影响

采用金属氧化物电子传输层(ETL)的聚合物光伏器件在制备完成之初通常性能表现低下, J-V曲线呈异常“S”形. 当器件受白光持续照射后, 该不良状况会逐渐好转, 此过程称为光浴(light-soaking). 光浴现象普遍被认为是ETL界面问题所致. 从器件结构着手, 研究了ZnO 纳米颗粒ETL相邻的两个界面在光浴问题上的作用. 制备了功能层相同的(电极除外)正型、反型器件及复合ETL结构器件, 发现光浴现象仅出现于包含ZnO/ITO界面的反型器件中, 证明该界面是导致光浴现象的主要原因. 分析认为: ZnO颗粒表面O₂吸附形成的电子陷阱增加了ITO/ZnO势垒厚度, 使得光生电子无法逾越而成为空间电荷积累, 从而导致器件初始性能不佳. 器件经光照后, ETL内部受激而生的空穴电子对填补了ZnO缺陷, 提升了ETL的电荷选择性并减小了界面势垒厚度, 被束缚的光生电子得以隧穿至ITO电极, 反型器件性能最终得以改善.     

Improved performance of silicon‐nanoparticle film‐coated dye‐sensitized solar cells

Silicon (Si) nanoparticles with average size of 13 nm and orange–red luminescence under UV absorption were synthesized using electrochemical etching of silicon wafers. A film of Si nanoparticles with thickness of 0.75 µm to 2.6 µm was coated on the glass (TiO₂ side) of a dye‐sensitized solar cell (DSSC). The cell exhibited nearly 9% enhancement in power conversion efficiency (η) at film thickness of ～2.4 µm under solar irradiation of 100 mW/cm² (AM 1.5) with improved fill factor and short‐circuit current density. This study revealed for the first time that the Si‐nanoparticle film converting UV into visible light and helping in homogeneous irradiation, can be utilized for improving the efficiency of the DSSCs. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dual plasmonic‐enhanced bulk‐heterojunction solar cell incorporating gold nanoparticles into solution‐processed anode buffer layer and active layer

A dual plasmonic resonance effect on the performance of poly(3‐hexylthiophene) (P3HT):phenyl C61‐butyricacid methyl ester (PC61BM) based polymer solar cells (PSCs) has been demonstrated by selectively incorporating 25 nm colloidal gold nanoparticles (Au NPs) in a solution‐processed molybdenum oxide (MoO₃) anode buffer layer and 5 nm colloidal Au NPs in the active P3HT:PCBM layer. The devices exhibit up to ～20% improvement in power conversion efficiency which is attributed to the dual effect of localized surface plasmon resonance (LSPR) of Au NPs with enhanced light absorption and exciton generation. Our report shows a guideline on the usage of dual LSPR effect for the solution‐processed polymer solar cells to achieve high efficiencies. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)