[Show abstract][Hide abstract] ABSTRACT: This paper reports on the development of an amorphous silicon cell used in the top cell of Micromorph® tandem solar modules produced in the pilot line of Oerlikon Solar in Trübbach — Switzerland. Tuning of the process parameters used for PECVD deposition of the absorber layers such as process pressure, RF power density, SiH4/H2 ratio, and substrate temperature can result in significant improvement in the material quality of the absorber layer and therefore in the performance and light induced degradation of the a-Si cell. We have measured the single layer properties of different absorber layers by infrared spectroscopy and have found a strong correlation between both the microstructure factor R and the H-content bonded to Si and the stabilized efficiency or relative degradation of the a-Si cells containing the corresponding absorber layers. A combination of absorber layers with superior material quality, adapted p-doped and buffer layers and ZnO front and back contacts with enhanced light trapping have achieved record values for the conversion efficiency of industrial thin a-Si single junction cells and modules. Our results show initial efficiencies on test cells prepared on 1.4 m2 substrates of over 11%, an active area efficiency of 10.5% for a champion 1.4 m2 a-Si single junction module and an 8.7% stabilized conversion efficiency for an industrial 1.4 m2 a-Si single junction champion module.
Journal of Non-Crystalline Solids 09/2012; 358(17):2264–2267. · 1.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: High efficiency large area thin film silicon solar modules require highly optimized front contacts based on transparent conductive oxides (TCO). In single layer TCO it is usually not possible to optimize independently the key parameters haze, total transmission and resistivity. In this work, we present results of scaling a multilayer TCO process from laboratory scale to large area (1.4 m 2) industrial production equipment from Oerlikon Solar. Combining two TCO sublayers with different dopant concentrations allows optimizing haze and resistivity independently.
[Show abstract][Hide abstract] ABSTRACT: In September 2010 the PEPPER project started after receiving a grant under the Framework Programme FP7 for research of the European Union, coordinated by the DG Energy of the European Commission (no. 249782). The PEPPER project tackles major factors relating to micromorph module efficiency and production cost by assessing the influences of glass, TCO and silicon deposition (including in-situ cleaning). The project bridges the gap between research and industrial application by executing new developments and improvements in the field of TCO and PECVD reactors and processes and transferring them to production plants where the full impact on module efficiency and costs can be evaluated. The joint goal of this project is the demonstration of a 157Wp (stable) micromorph module with a cost of ownership (CoO) of 0.5€/Wp. Succeeding in this project will ensure the competitiveness of the Micromorph technology and further approach the final goal of grid parity. The first results of the project have already shown efficiency improvement by both narrow gap reactor and advanced TCO concepts.
[Show abstract][Hide abstract] ABSTRACT: Polycrystalline ZnO:B deposited by low-pressure chemical vapor deposition (LPCVD) was proven as an efficient electrode material for thin film silicon solar cells application, thanks to high transparency, good electrical conductivity and strong light scattering via self-textured surface. However, high doping used to lower resistivity of ZnO films, induces free carrier absorption (FCA), detrimental to current generation in the bottom microcrystalline cell of a micromorph device. Here we describe optimized 2 μm thick LPCVD ZnO:B bilayers, combining of a thin nucleation layer, plus a bulk layer, having different doping levels. This arrangement in one growth-step enables a separate control of electrical and optical properties of the films. It promotes the growth of strongly light diffusive structures with enhanced electron mobility (∼45cm2/Vs) and low electron density (∼2×1019 cm−3). This results in low FCA and moderate sheet resistance, that should easily be lowered to
IEEE Journal of Photovoltaics 01/2011; 2(2):002578-002578. · 3.00 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This work reports on the optimization of amorphous-microcrystalline silicon tandem solar cells and modules on LPCVD ZnO on 1.4m2 substrate size. The focus is on the optimization of PECVD deposition of n-and p-type doped layers for the microcrystalline silicon bottom cell deposited in a commercially available Oerlikon Solar KAI PECVD system. For this type of layers, both electro-optical properties with respect to cell and module efficiency as well as deposition rate with respect to throughput are of interest. A novel silicon oxide based n-layer which enhances current density of the solar cell by reducing absorption loss was introduced in the bottom cell design. An appropriate optimization of the n-layer was found crucial to achieve a suitable device performance. In a second step, the increase of the deposition rate of the n-and p-layers was addressed to match the throughput requirements for an industrial low cost production process.
Conference Record of the IEEE Photovoltaic Specialists Conference 01/2011;
[Show abstract][Hide abstract] ABSTRACT: Large area (1.4 m 2) thin film photovoltaic modules require precise control of the deposition uniform-ity. The efficiency of modules based on hydrogenated amorphous silicon (a-Si:H) and tandem modules based a-Si:H/microcrystalline silicon (µc-Si:H) can be strongly enhanced by optimizing light trapping induced by the front contact transparent conductive oxide (TCO). One of the most important parameters to quantify light trapping is the TCO haze. In this work, we present a large area mapping haze measurement system and we show how to use such a system for characterization and optimization of Zinc Oxide TCO front contacts produced by LPCVD (low pressure chemical vapour deposition). Simulations are used to show the relation between TCO coating uniformity and mod-ule performance.
[Show abstract][Hide abstract] ABSTRACT: This work reports on the development of a new economically attractive a-Si process with high efficiency on LPCVD ZnO. It comprises an amorphous p-layer and a modified single chamber process for improved interfaces. A 1cm 2 a-Si record cell with 11.0% initial efficiency was obtained at about four times reduced process time for the p-layer deposition compared to the commonly used µc-Si/a-Si double p-layer. The high FF and Voc together with a low series resistance demonstrate the excellent quality of the LPCVD ZnO/a-Si p contact. The new a-Si process was successfully up-scaled to 1.4 m 2 modules yielding 10.3% initial active area efficiency for a a-Si module and 11.1% initial active area efficiency for a a-Si/µc-Si module.
[Show abstract][Hide abstract] ABSTRACT: Large area (1.4 m 2) thin film photovoltaic modules require precise control of the deposition uniformity. Most metrology tools focus either on the spatially resolved measurement of single layers or on the measurement of the performance of a module as a whole. We present a new tool to map the quantum efficiency of a module. Mapping quantum efficiency measurements of large area modules combines the well known functionality of quantum efficiency measurements with spatially resolved information. This unique combination enables in-depth optimization of both a-Si:H and tandem a-Si:H/µc-Si modules. This paper shows examples of the application of mapping QE measurements at OC Oerlikon Solar.
[Show abstract][Hide abstract] ABSTRACT: In this paper an overview of our developments towards industrialization of thin film silicon PV modules is presented. Amorphous silicon p-i-n solar cells have been developed in medium size single-chamber R&D KAI-M PECVD reactors. High initial efficiencies of 10.6 % and stabilized of 8.6 % could be achieved for a 1 cm2 a-Si:H p-i-n solar cell of 0.20 m thick i-layer deposited on TCO from Asahi U type (SnO2). On our in-house developed LPCVD ZnO we could further improve the stabilized a-Si:H p-i-n efficiency to a similar level of 8.5 %. Incorporating such cells in commercial available front TCO of lower quality still leads to high initial mini-module aperture efficiencies (10 × 10 cm2) of 9.1% and stabilized ones of 7.46% (independently measured by ESTI JRC-Ispra).Transferring the processes from the KAI-M to the industrial size 1.1×1.25 m2 KAI-1200 R&D reactors resulted in a-Si:H modules of 110.6 W using commercial TCO, respectively 112.4 W when applying in-house developed LPCVD front ZnO. Both initial module performances have been independently measured by ESTI laboratories of JRC Ispra. A typical temperature coefficient for the module power of -0.22 %/°C (relative loss) has been deduced from temperature dependent I-V characteristics at ESTI laboratories of JRC Ispra. Finally, micromorph mini-modules of 10 % initial aperture efficiency have been fabricated.
[Show abstract][Hide abstract] ABSTRACT: Highly conductive and transparent aluminum-doped zinc oxide (ZnO:Al) films were prepared by reactive mid-frequency (MF) magnetron sputtering at high growth rates. By varying the deposition pressure, pronounced differences with respect to film structure and wet chemical etching behavior were obtained. Optimized films develop good light-scattering properties upon etching leading to high efficiencies when applied to amorphous (a-Si:H) and microcrystalline (μc-Si:H) silicon-based thin-film solar cells and modules. Initial efficiencies of 7.5% for a μc-Si:H single junction and 9.7% for an a-Si:H/μc-Si:H tandem module were achieved on an aperture area of 64 cm2.
[Show abstract][Hide abstract] ABSTRACT: Amorphous silicon p-i-n solar cells and modules have been developed in small R& D KAI reactors. Test cells of 0.25 mum thick i-layer exceed 10 % initial efficiencies and stabilized ones of 8.2 %. The a-Si:H deposition process is successfully transferred to industrial size substrates of 1.4 m<sup>2</sup> area resulting in initial module powers of 106.4 W using a commercial TCO front AFG and, recently, 104.1 W using in-house developed LPCVD front ZnO. For both modules our in-house LPCVD ZnO has been applied as back contact. The former large-area module passed successfully the damp-heat test. Entirely microcrystalline p-i-n cells with an efficiency of 8.5 % could be prepared in a single-chamber KAI-S reactor. Micromorph tandems resulted in initial cell efficiencies of 10.7 %, whereas mini-modules lead to initial aperture efficiencies of 10.2 %
Photovoltaic Energy Conversion, Conference Record of the 2006 IEEE 4th World Conference on; 06/2006
[Show abstract][Hide abstract] ABSTRACT: ZnO:Al films were prepared on glass substrates by RF and DC sputtering from ceramic ZnO:Al2O3 targets. The film properties of RF sputtered ZnO:Al showed a weak dependence on film thickness and substrate temperature while a strong dependence on sputter pressure and oxygen addition to the process gas was observed. For DC sputtering in static mode at 270 °C a low resistivity of 2.3–5 × 10− 4 Ω cm was obtained in a wide pressure range of 0.04 to 4 Pa. At lower substrate temperatures the supply of small amounts of oxygen was required to maintain high transparency and achieve significant roughness for light scattering after wet chemical etching. Highest damp heat stability was found for ZnO:Al films deposited at low sputter pressures. This behavior could be correlated to the highly compact film structure of these films. ZnO:Al films deposited in dynamic DC mode exhibited inferior resistivity of 8–40 × 10− 4 Ω cm, which partly could be attributed to the specific design of the inline sputter system.
[Show abstract][Hide abstract] ABSTRACT: Aluminum doped zinc oxide (ZnO:Al, AZO) films were prepared by reactive mid frequency magnetron sputtering. We characterized the electrical and optical properties as well as the surface morphology obtained after wet chemical etching. The carrier mobility could be increased up to 42 cm(2)/Vs and the transmission between 400 and 1100 nm was enhanced by the reduction of aluminum content in the targets. The working point of the reactive sputtering process strongly influences the etching behavior and was used to optimize the light scattering properties of the ZnO:Al films after wet chemical etching. Finally, the texture-etched ZnO:Al films were successfully applied as substrates for silicon thin film solar cells. (c) 2005 Elsevier B.V All rights reserved.
Thin Solid Films 01/2006; 502(1-2):286-291. · 1.87 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In superstrate thin-film solar cells a surface texture of the transparent conductive oxide (TCO) front contact is used to enhance short-circuit currents by both increasing the light input into the cell from refractive index grading and causing light trapping from optical scattering. The haze and root-mean-square roughness are inadequate to quantitatively account for increased light absorption and hence enhanced short-circuit currents. Rather, angle-resolved scattering combined with scattering-efficient components of the texture details were evaluated for different types of TCO materials to yield a fairly universal correlation between short-circuit currents and large-angle scattering, weighted by a texture-dependent scattering efficiency.
Photovoltaic Specialists Conference, 2005. Conference Record of the Thirty-first IEEE; 02/2005
[Show abstract][Hide abstract] ABSTRACT: This study addresses the electrical and optical properties of radio frequency magnetron sputtered aluminum doped zinc oxide (ZnO:Al) films. The main focus was on the improvement in carrier mobility mu to achieve simultaneously high transparency for visible and particularly near-infrared light and low resistivity. The influence of Al concentration in the target, film thickness, sputter power, deposition pressure, and substrate temperature on material properties was investigated. The structural, compositional, electrical and optical properties were studied using x-ray diffraction, secondary ion mass spectrometry (SIMS), room temperature Hall effect measurements and spectral photometry, respectively. All ZnO:Al films were polycrystalline and preferentially oriented along . The grain size along the direction of growth increased with higher Al doping and with increasing film thickness. The SIMS measurements revealed that the Al concentration in the film was nearly the same as in the target. Carrier concentration N and mobility mu are determined by the target Al concentration. In addition mu is influenced by the film thickness and the sputter pressure. For each Al concentration, the highest mu was generally observed at low deposition pressures. By using a target with low Al2O3 concentration of 0.5 wt %, mu could be improved up to 44.2 cm2/V s while maintaining the electrical resistivity rho as low as 3.8×10-4 Omega cm. For these films the transparency in the near-infrared wavelength range strongly improved which makes them particularly interesting for the application in optoelectronic devices like thin-film solar cells. The mu-N dependence for films deposited under diverse conditions was studied to identify a practical limit for mu.
Journal of Applied Physics 01/2004; 95:1911-1917. · 2.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper addresses the development of silicon thin film solar cells by plasma-enhanced chemical vapour deposition (PECVD) at 13.56 MHz excitation frequency. For an efficient light trapping we focus on textured ZnO:Al films prepared by sputtering and post deposition wet chemical etching. These films were optimised with respect to conductivity, transparency and film structure, the latter one controlling the surface texture obtained after etching. A-Si:H//spl mu/c-Si:H tandem cells yielded stable efficiencies up to 11.2% for a cell area of 1 cm/sup 2/. Initial module efficiencies of 10.8% and 10.1% were achieved for aperture areas of 64 cm/sup 2/ and 676 cm/sup 2/, respectively.
Photovoltaic Energy Conversion, 2003. Proceedings of 3rd World Conference on; 06/2003