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25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion, 6-10 September 2010, Valencia, Spain; 2896-2898, Sunfilm is the first producer of thin film silicon tandem junction modules on large substrate size (2,60x2,20 m2) using Applied Materials AKT PECVD systems. The company is scaling up its production facilities in Grossroehrdorf to a nominal output capacity of 2x60 MW/year. In April 2009, the final acceptance test (FAT) was achieved and production 24/7 has started in line 1. IEC product certification was achieved in June 2009. In January 2010 the FAT was achieved in line 2. Currently, Sunfilm is focusing on product development, line stabilization and cost reduction. The company has recently reached very high module efficiencies and offers a wide range of products. The line flexibility allows production of additional size formats between 1.4 and 5.7 m2. All Sunfilm products demonstrate better electrical yield kWh per installed MWp than conventional crystalline Si modules. In this paper the current status of module development and production at Sunfilm is presented. Special emphasis is given to the oneyear production and product experience.

25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion, 6-10 September 2010, Valencia, Spain; 3158-3160, Module performance in large area thin film PV production crucially depends on homogeneous electrical performance of the module’s network of individual cells. We present I-V measurements of a standard a-Si/μc-Si tandem module and of its single cells. The distribution of single cell performance data is compared to module performance data to trace the influences of various inhomogeneities on overall panel performance. We estimate the theoretical potential of relative efficiency improvement resulting from removal of inhomogeneities to be 3% - 4%. Our study facilitates identification and minimization of performance-relevant inhomogeneities.

25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion, 6-10 September 2010, Valencia, Spain; 3073-3075, Dielectric intermediate reflector layers in thin-film silicon tandem solar cells with randomly textured interfaces are used to optimize current matching and finally the energy conversion efficiency of the whole device. We integrated a 3D photonic crystal as an intermediate reflector layer between an amorphous silicon top cell and a microcrystalline silicon bottom cell. The reflectivity of the 3D photonic thin-film intermediate layer device is designed and optimized for a state-of-the-art tandem solar cell which leads to an enhancement of the external quantum efficiency within the amorphous silicon top cell. Our prototype shows an enormous gain of the external quantum efficiency in the in the weak absorption spectrum of the top cell and nearly no loss for short wavelength.

25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion, 6-10 September 2010, Valencia, Spain; 3117-3119, In order to increase the deposition rate of hydrogenated amorphous silicon (a-Si:H) and microcrystalline (μc-Si:H) layers high plasma excitation frequencies ( > 13.56 MHz) are commonly used. However, scaling to squaremeter size in industrial production has been challenging, e.g. due to poor layer uniformity. In our inline PECVD production tool for a-Si/μc-Si tandem modules (1.78 m2) at Sunfilm AG we currently use RF (13.56 MHz) PECVD for both a-Si and μc-Si deposition. In this study, a-Si:H layers deposited by VHF PECVD at 40.68 MHz have been investigated in large area tandem modules. In order to maintain layer uniformity across the 1.78 m2 substrate at high deposition rates (0.3 – 0.4 nm/s), deposition conditions such like working pressure, hydrogen dilution ratio and VHF input power have been optimized. However, there were no hardware changes except generator and matching unit to the previous RF system. Compared to modules fabricated by RF-PECVD, 50 - 80% higher deposition rates have been achieved at the same stabilized total-area module efficiency. Additionally, light-induced degradation was smaller for the modules prepared by VHF-PECVD.

25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion, 6-10 September 2010, Valencia, Spain; 3174-3176, We report on Sunfilm’s recent development of ZnO:Al layers for front contact TCO in a-Si/μc-Si tandem modules. Our new process allows to produce ZnO:Al layers of excellent optical and electrical properties on 1.78 m2 float glass substrates in an industrial DC sputter line. After etching in diluted hydrochloride acid, the TCO exhibits haze values > 60 % at 700 nm and a surface texture tailored for a-Si/μc-Si tandem modules. TCO with such properties is usually obtained using lab scale RF sputter processes only, which, however, have too low deposition rates and are difficult to scale to large areas for industrial application. On the new TCO substrates a-Si/μc-Si tandem modules with a stabilized total area efficiency of 8.3 % have been produced at Sunfilm. This is comparable to our typical module performance on commercial SnO2:F based TCO substrates.

25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion, 6-10 September 2010, Valencia, Spain; 3269-3272, The influence of in situ NF3 chamber cleaning on a-Si/μc-Si tandem device performance has been investigated on 1.78-m2 modules produced in an industrial inline PECVD production line. After the cleaning process, the module output power drops compared to the last deposition cycle, but recovers gradually with increasing number of depositions. This “chemical memory effect” (CME) of the early modules is likely to be caused by fluorine chamber contamination from NF3:Ar plasma, since SIMS measurement results show that fluorine content in the film decreases with increasing number of depositions. I-V measurements on small-area cells have shown that the module performance as a whole is mainly limited by cells with low current, located at the module edges, where the fluorine contamination from chamber walls is likely to be higher. It has been found that the position dependence of the CME after NF3 cleaning results from deteriorated microcrystalline bottom cells around the module edges. In order to minimize this effect, deposition condition as well as module fabrication method were optimized especially for the early modules.