Electron‐beam crystallized large grained silicon solar cell on glass substrate

Thin film hetero‐emitter solar cells with large‐grained poly‐silicon absorbers of around 10 µm thickness have been prepared on glass. The basis of the cell concept is electron‐beam‐crystallization of an amorphous or nanocrystalline silicon layer deposited onto a SiC:B layer. The SiC:B layer covers a commercially well available glass substrate, serving as diffusion barrier, contact layer and dopand source. For silicon absorber deposition a low pressure chemical vapour deposition was used. The successively applied e‐beam crystallization process creates poly‐silicon layers with grain sizes up to 1 × 10 mm² with low defect densities. The high electronic quality of the absorber is reflected in open circuit voltages as high as 545 mV, which are realized making use of the well‐developed a‐Si:H hetero‐emitter technology. Copyright © 2011 John Wiley & Sons, Ltd.     

Silicon thin‐film solar cells with rectangular‐shaped grating couplers

As an alternative to randomly textured transparent conductive oxides as front contact for thin‐film silicon solar cells the application of transparent grating couplers was studied. The grating couplers were prepared by sputtering of aluminium‐doped zinc oxide (ZnO) on glass substrate, a photolithography and a lift‐off process and were used as periodically textured substrates. The period size and groove depth of these transparent gratings were tuned independently from each other and varied between 1 and 4 μm and 100–600 nm. The optical properties of rectangular‐shaped gratings and the opto‐electronic behaviour of amorphous and microcrystalline silicon solar cells with integrated grating couplers as a function of the grating parameters (period size P and groove depth h_g) are presented. The optical properties of the gratings are discussed with respect to randomly textured substrates and the achieved solar cell results are compared with the opto‐electronic properties of solar cells deposited on untextured (flat) and randomly textured substrates. Copyright © 2005 John Wiley & Sons, Ltd.     

UV nanoimprint for the replication of etched ZnO:Al textures applied in thin‐film silicon solar cells

In this work, we present a technology for a high precision nanostructure replication process based on ultraviolet nanoimprint lithography for the application in the field of thin‐film photovoltaics. The potential of the technology is demonstrated by the fabrication of microcrystalline silicon thin‐film prototype solar cells. The high accuracy replication of random microstructures made from sputtered and etched ZnO:Al, used to scatter the incident light in thin solar cells, is shown by local topography investigations of the same 7.5 × 7.5 µm² area on the master and the replica. Different types of imprint resists and imprint moulds were investigated to find the optimal, high precision replication technology. Two types of thin‐film silicon solar cells, in p‐i‐n and n‐i‐p configuration, were fabricated to study the potential of the imprint technology for different applications. It is shown that solar cells deposited on an imprinted glass hold similar performances compared with reference solar cells fabricated with a standard process on textured ZnO:Al. Thus, it is demonstrated that the replication of light scattering structures by using an imprint process is an attractive method to decouple the scattering properties from the layer forming the electrical front contact. Because a simple and cheap high throughput process is used, this study additionally proves the relevance for the industrial mass production in the field of photovoltaics. Copyright © 2013 John Wiley & Sons, Ltd.     

Optical properties of thin‐film silicon solar cells with grating couplers

The effect of grating couplers on the optical properties of silicon thin‐film solar cells was studied by a comparison of experimental results with numerical simulations. The thin‐film solar cells studied are based on microcrystalline silicon (μc‐Si:H) absorber layers of thickness in the micrometer range. To investigate the light propagation in these cells, especially in the red wavelength region, three‐dimensional power loss profiles are simulated. The influence of different grating parametres—such as period size, groove height, and shape of the grating—was studied to gain more insight into the light propagation within thin‐film silicon solar cells and to determine an optimized light trapping scheme. The effect of the TCO front and TCO back side layer thickness was investigated. The calculated quantum efficiencies and short‐circuit current densities are in good agreement with the experimental data. The simulations predict further optimization criteria. Copyright © 2006 John Wiley & Sons, Ltd.     

Two‐dimensional modeling of front contact silicon solar cells

The modeling of a new type of silicon solar cell intended for operation at very high concentration, with all the contacts at its front face, is presented. The two‐dimensional model developed makes use of the theory of the complex variable, and is able to explain the main features of the operation of these cells. It is shown that if all the parameters reach good state‐of‐the‐art values, and with the appropriate layout, this structure can reach 25% efficiency for a range of concentrations wider than any other known silicon cell. Copyright © 2004 John Wiley & Sons, Ltd.     

A new 2D model for the electrical potential in a cell stripe in thin‐film solar modules including local defects

The performance of solar modules is strongly influenced by the presence of local defects (shunts) in the module. Modeling cell stripes with local defects requires at least a 2D model. Most works on such 2D models are based on the numerical solution of the involved differential equations. These numerical models are quite computationally intensive and hence tedious for applications that require many evaluations of the model, for example, fitting experiments, computing accurate current/voltage characteristics, and finding a maximum power point. In this work, we present a fast 2D model for a cell stripe based on the superposition of several analytical expressions. This model uses a linearization of the solar cell current/voltage characteristics and takes the sheet resistance of one electrode into account (i.e., the other electrode is assumed to be a perfect conductor). With our model, the potential distribution in a cell stripe in the presence of local shunts can be computed in a matter of seconds. The model has been made freely available. Copyright © 2013 John Wiley & Sons, Ltd.     

PI衬底柔性透明硅薄膜太阳能电池的制备及性能

利用硬质玻璃为载板,采用传统硅薄膜太阳能电池生产设备,在聚酰亚胺(PI)塑料薄膜衬底上沉积了B掺杂的ZnO(BZO)薄膜,并以此作为前电极制备了单节电池结构及多节串联一体结构的非晶硅(a-Si)太阳能电池;研究了PI衬底上BZO薄膜的光学及电学性能。结果表明,PI衬底上沉积BZO薄膜后在300~1 200 nm波长范围的透光率为76.63%,方块电阻19.7?/□。所制备的单节和多节串联一体结构的a-Si薄膜太阳能电池的转化效率分别达到6.45%和5.1%,封装后电池组件具有一定的透光性,透光率约达到30.2%。     

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.     

Improved conversion efficiency of a‐Si:H/µc‐Si:H thin‐film solar cells by using annealed Al‐doped zinc oxide as front electrode material

In recent years, zinc oxide has been investigated as a front electrode material in hydrogenated amorphous silicon/hydrogenated microcrystalline silicon (a‐Si:H/µc‐Si:H) tandem solar cells. Such as for other transparent conducting oxide materials and applications, a proper balancing of transparency and conductivity is necessary. The latter is directly related to the density and the mobility of charge carriers. A high density of charge carriers increases conductivity but leads to a higher absorption of light in the near‐infrared part of the spectrum due to increased free‐carrier absorption. Hence, the only way to achieve high conductivity while keeping the transparency as high as possible relies on an increase of carrier mobility. The carrier density and the mobility of sputtered Al‐doped zinc oxide (ZnO:Al) can be tailored by a sequence of different annealing steps. In this work, we implemented such annealed ZnO:Al films as a front electrode in a‐Si:H/µc‐Si:H tandem solar cells and compared the results with those of reference cells grown on as‐deposited ZnO:Al. We observed an improvement of short‐circuit current density as well as open‐circuit voltage and fill factor. The gain in current density could be attributed to a reduction of both sub‐band‐gap absorption and free‐carrier absorption in the ZnO:Al. The higher open‐circuit voltage and fill factor are indicators of a better device quality of the silicon for cells grown on annealed ZnO:Al. Altogether, the annealing led to an improved initial conversion efficiency of 12.1%, which was a gain of +0.7% in absolute terms. Copyright © 2013 John Wiley & Sons, Ltd.     

World‐record Cu(In,Ga)Se2‐based thin‐film sub‐module with 17.4% efficiency

We report a new certified world‐record efficiency for thin‐film Cu(In,Ga)Se₂‐based photovoltaic sub‐modules of 17.4% (aperture area). The record efficiency of the 16 cm², monolithically integrated, sub‐module has been independently confirmed by Fraunhofer ISE. The record device is the result of extensive co‐optimization of all processing steps. During the optimization process, strong focus has been put on the scalability of processes to cost‐effective mass production, as reflected, for example, in Cu(In,Ga)Se₂ deposition time and substrate temperature. Device manufacturing as well as results of electrical and material characterization is discussed. Copyright © 2012 John Wiley & Sons, Ltd.     

Deposition of intrinsic hydrogenated amorphous silicon for thin‐film solar cells – a comparative study for layers grown statically by RF‐PECVD and dynamically by VHF‐PECVD

Hydrogenated amorphous silicon (a‐Si:H) is conventionally deposited using static plasma‐enhanced chemical vapor deposition (PECVD) processes. In this work, a very high frequency (VHF) dynamic deposition technique is presented, on the basis of linear plasma sources. This configuration deploys a simple reactor design and enables continuous deposition processes, leading to a high throughput. Hence, this technique may facilitate the use of flexible substrates. As a result, the production costs of thin‐film silicon solar cells could be reduced significantly. We found a suitable regime for the homogeneous deposition of a‐Si:H layers for growth rates from 0.35–1.1 nm/s. The single layer properties as well as the performance of corresponding a‐Si:H solar cells are investigated and compared with a state‐of‐the‐art radio frequency (RF) PECVD regime. By analyzing the Fourier transform infrared spectroscopy spectra of single layers, we found an increasing hydrogen concentration with deposition rate for both techniques, which is in agreement with earlier findings. At a given growth rate, the hydrogen concentration was at the same level for intrinsic layers deposited by RF‐PECVD and VHF‐PECVD. The initial efficiency of the corresponding p–i–n solar cells ranged from 9.6% at a deposition rate of 0.2 nm/s (RF regime) to 8.9% at 1.1 nm/s (VHF regime). After degradation, the solar cell efficiency stabilized between 7.8% and 5.9%, respectively. The solar cells incorporating intrinsic layers grown dynamically using the linear plasma sources and very high frequencies showed a higher stabilized efficiency and lower degradation loss than solar cells with intrinsic layers grown statically by RF‐PECVD at the same deposition rate. Copyright © 2012 John Wiley & Sons, Ltd.     

N 型背接触晶硅太阳电池前表面场研究

利用 Silvaco 公司的 Athena 工艺仿真软件和 Atlas 器件仿真软件,对 N 型插指背结背接触(InterdigitatedBack Contact,IBC)晶硅太阳电池普遍采用的前表面场（FSF）结构进行研究,详细分析了 IBC 晶硅电池 FSF 表面掺杂浓度及扩散深度对电池性能的影响。结果表明：具有不同表面掺杂浓度和扩散深度的 FSF 对 IBC 晶硅太阳电池短路电流密度(Jsc)、开路电压(Voc)和填充因子(FF)产生显著影响,从而影响电池的转换效率(Eff)。具有较低表面浓度、深扩散 FSF 结构的 IBC 晶硅太阳电池可获得较高转换效率,当表面掺杂浓度为 5×1017cm–3时,电池转换效率Eff最高,且随 FSF 扩散深度增加略有增加,最高转换效率可达 22.3%。     

A 3‐in‐1 doping process for interdigitated back contact solar cells exploiting the understanding of co‐diffused dopant profiles by use of PECVD borosilicate glass in a phosphorus diffusion

Boron and phosphorus doping of crystalline silicon using a borosilicate glass (BSG) layer from plasma‐enhanced chemical vapor deposition (PECVD) and phosphorus oxychloride diffusion, respectively, is investigated. More specifically, the simultaneous and interacting diffusion of both elements through the BSG layer into the silicon substrate is characterized in depth. We show that an overlying BSG layer does not prevent the formation of a phosphorus emitter in silicon substrates during phosphorus diffusion. In fact, a BSG layer can even enhance the uptake of phosphorus into a silicon substrate compared with a bare substrate. From the understanding of the joint diffusion of boron and phosphorus through a BSG layer into a silicon substrate, a model is developed to illustrate the correlation of the concentration‐dependent diffusivities and the emerging diffusion profiles of boron and phosphorus. Here, the in‐diffusion of the dopants during diverse doping processes is reproduced by the use of known concentration dependences of the diffusivities in an integrated model. The simulated processes include a BSG drive‐in step in an inert and in a phosphorus‐containing atmosphere. Based on these findings, a PECVD BSG/capping layer structure is developed, which forms three different n⁺⁺−, n⁺− and p⁺−doped regions during one single high temperature process. Such engineered structure can be used to produce back contact solar cells. Copyright © 2016 John Wiley & Sons, Ltd.     

Polycrystalline silicon thin film transistors fabricated in various solid phase crystallized films deposited on glass substrates

In this work, we have characterized various types of polysilicon films, crystallized upon thermal annealing from films deposited by low pressure chemical vapor deposition in the amorphous phase and a mixed phase using silane or in the amorphous phase using disilane. Polysilicon thin film transistors (TFTs) were fabricated, at low processing temperatures, in these three types of films on high strain point Corning Code 1734 and 1735 glass substrates. Double layer films, with the bottom layer deposited in a mixed phase and the top in the amorphous phase, allowed TFT fabrication at a drastically reduced thermal budget; optimum values of thicknesses and deposition rates of the layers are reported for reducing the crystallization time and improving film quality. Optimum deposition conditions for TFT fabrication were also obtained for films deposited using disilane. The grain size distribution for all types of films was shown to be wider for a larger grain size. Fabricated TFTs exhibited field effect electron mobility values in the range of 20 to 50 cm²/V·s, subthreshold swings of about 0.5–1.5 V/dec and threshold voltage values of 2–4 V.     

Preparation and measurement of highly efficient a‐Si:H single junction solar cells and the advantages of μc‐SiOx:H n‐layers

Reducing the optical losses and increasing the reflection while maintaining the function of doped layers at the back contact in solar cells are important issues for many photovoltaic applications. One approach is to use doped microcrystalline silicon oxide (μc‐SiO_x:H) with lower optical absorption in the spectral range of interest (300 nm to 1100 nm). To investigate the advantages, we applied the μc‐SiO_x:H n‐layers to a‐Si:H single junction solar cells. We report on the comparison between amorphous silicon (a‐Si:H) single junction solar cells with either μc‐SiO_x:H n‐layers or non‐alloyed silicon n‐layers. The origin of the improved performance of a‐Si:H single junction solar cells with the μc‐SiO_x:H n‐layer is identified by distinguishing the contributions because of the increased transparency and the reduced refractive index of the μc‐SiO_x:H material. The solar cell parameters of a‐Si:H solar cells with both types of n‐layers were compared in the initial state and after 1000 h of light soaking in a series of solar cells with various absorber layer thicknesses. The measurement procedure for the determination of the solar cell performance is described in detail, and the measurement accuracy is evaluated and discussed. For an a‐Si:H single junction solar cell with a μc‐SiO_x:H n‐layer, a stabilized efficiency of 10.3% after 1000 h light soaking is demonstrated. Copyright © 2015 John Wiley & Sons, Ltd.     

DC‐sputtered ZnO:Al as transparent conductive oxide for silicon heterojunction solar cells with µc‐Si:H emitter

Silicon heterojunction (SHJ) solar cells are highly interesting, because of their high efficiency and low cost fabrication. So far, the most applied transparent conductive oxide (TCO) is indium tin oxide (ITO). The replacement of ITO with cheaper, more abundant and environmental friendly material with texturing capability is a promising way to reduce the production cost of the future SHJ solar cells. Here, we report on the fabrication of the SHJ solar cells with direct current‐sputtered aluminum‐doped zinc oxide (ZnO:Al) as an alternative TCO. Furthermore, we address several important differences between ITO and the ZnO:Al layers including a high Schottky barrier at the emitter/ZnO:Al interface and a high intrinsic resistivity of the ZnO:Al layers. To overcome the high Schottky barrier, we suggest employing micro‐crystalline silicon (µc‐Si:H) emitter, which also improves temperature threshold and passivation of the solar cell precursor. In addition, we report on the extensive studies of the effect of the ZnO:Al deposition parameters including layer thickness, oxygen flow, power density and temperature on the electrical properties of the fabricated SHJ solar cells. Finally, the results of our study indicate that the ZnO:Al deposition parameters significantly affect the electrical properties of the obtained solar cell. By understanding and fine‐tuning all these parameters, a high conversion efficiency of 19.2% on flat wafer (small area (5 × 5 mm²) and without any front metal grid) is achieved. Copyright © 2014 John Wiley & Sons, Ltd.     

Analysis of short circuit current gains by an anti‐reflective textured cover on silicon thin film solar cells

The influence of a retro‐reflective texture cover on light in‐coupling and light‐trapping in thin film silicon solar cells is investigated. The texture cover is applied to the front glass of the cell and leads to a reflectance as low as r ≈ 3% by reducing the reflection at the air/glass interface and indirectly also reducing the reflections from the internal interfaces. For weakly absorbed light in the long wavelength range, the texture also enhances the light‐trapping in the solar cell. We demonstrate an increase of the short circuit current density of exemplary investigated thin film silicon tandem solar cells by up to 0.95 mA cm⁻² and of the conversion efficiency by up to 0.74% (absolute). For a planar microcrystalline solar cell, the enhancement of light‐trapping was determined from the reduced reflection in the long wavelength range to be up to 17%, leading to an increase of the external quantum efficiency of up to 12%. Copyright © 2012 John Wiley & Sons, Ltd.     

Impurity‐to‐efficiency simulator: predictive simulation of silicon solar cell performance based on iron content and distribution

We present a simulation tool that predicts solar cell efficiency based on iron content in as‐grown wafer and solar cell processing conditions. This “impurity‐to‐efficiency” (I2E) simulation tool consists of three serial components, which are independently and jointly validated using published experimental results: (1) a kinetic model that calculates changes in the distribution of iron and phosphorus atoms during annealing; (2) an electronic model that predicts depth‐dependent minority carrier lifetime based on iron distribution; and (3) a device simulator that predicts solar cell performance based on the minority carrier lifetime distribution throughout the wafer and the device architecture. The I2E model is demonstrated to be an effective predictor of cell performance for both single‐crystalline and multi‐crystalline silicon solar cells. We demonstrate the process optimization potential for the I2E simulator by analyzing efficiency improvements obtained using low‐temperature annealing, a processing concept that has been successfully applied to achieve higher solar cell efficiencies on Fe‐contaminated materials. Copyright © 2010 John Wiley & Sons, Ltd.     

低温制备柔性染料敏化太阳电池TiO2薄膜电极

采用丝网印刷技术在柔性基底ITO/PET上制备TiO2多孔薄膜,经过低温烧结得到TiO2多孔薄膜电极。以D102染料为敏化剂,KI/I2为电解质,Pt电极为对电极,制成电池后测试了电池的光电性能。结果表明:以乙醇作为分散剂添加到P25粉体中,采用丝网印刷技术制膜,100℃低温烧结可以在柔性基底ITO/PET上制备出表面粗糙度良好、具有一定光电性能的TiO2多孔薄膜电极,用其制作的太阳电池转换效率达1.33%。