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35th European Photovoltaic Solar Energy Conference and Exhibition; 1573-1577, The energy yield of PV systems with horizontal single-axis tracking and bifacial panels was calculated using BIGEYE. BIGEYE is a versatile code developed at ECN part of TNO to calculate the yield of bifacial PV. Comparison to recent measured data with the BIFOROT set-up at the Zurich University of Applied Sciences showed very good agreement. Our BIGEYE results show that the bifacial energy gain and the tracking gain are mostly additive, making the combination of bifacial panels and tracking a very attractive option. For two different locations, Doha and Amsterdam, increases of energy yield in the order of 25% compared to monofacial, fixed tilt systems are possible at relatively modest ground cover values.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 1605-1609, The optimum mounting condition for bifacial modules is a trade-off maximizing the performance of the front and backside output obtained for the given installation conditions. At the backside of bifacial PV modules there are more complex conditions concerning the illumination intensity and illumination homogeneity, compared to the frontside. In extended PV plants, with parallel rows of bifacial modules, there are additional factors, such as reduced ground albedo due to shading by adjacent rows, which have to be considered. At the ZHAW, we implemented an outdoor test system to analyse the performance of bifacial arrays at differing mounting conditions by a new methodical measurement approach. The tilt angle is adjusted periodically between 0° and 90° in twelve positions within a one minute interval. In this paper we focus on outdoor measurement results concerning the illumination homogeneity at the front and backside and its impact on the total output. Not only the module data itself is analysed, but also a set of multiple small light sensors is attached at the rim of the bifacial centre module in order to reveal the illumination homogeneity in more detail. This setup enables a detailed analysis of the sensitivity at different tilt angles as well as more general yield results from long-term measurements.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 2184-2190, PV systems using bifacial solar modules have shown an increased energy harvest compared to systems with standard, monofacial panels. Due to bifaciality of the modules, the tilt angle, the installation height, the distance between the modules and in particular the ground reflectance have a significant influence on the energy harvest. For bifacial module arrays reflective elements in between the rows might be an option in order to achieve a low light concentration resulting in a further increased energy harvest. A simulation of such conditions is hardly possible; measurements at real systems would require considerable effort. In this work we present results obtained by a measuring setup with rotating mini modules. In particular the influence of the ground reflection was studied by using various grounds and reflecting elements with different shapes. Prior to the analysis of the reflector elements the measurement setup is described and the assignability of results from the miniaturized test array to a corresponding large scale system is demonstrated.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 56-60, A new concept for light weight solar modules is presented in this paper. The main difference to the common module type is the replacement of the frame at the laminates fringe by a lattice-like structure at the rear or at the rear and front side. Due to the smaller distances between the mechanical supporting elements the stiffness of the laminate itself can be reduced to a minimum, enabling the use of thin glass or alternative materials like for example polymer foils.

31st European Photovoltaic Solar Energy Conference and Exhibition; 2680-2685, With decreasing subsidies for PV energy fed into the grid other economic incentives are needed to sustain the growth of PV power. An effective solution is to increase self-consumption for grid-connected, residential PV systems by means of generating hot water by the use of a heat pump. This widely used concept of thermal energy storage has been adapted for a facade element with integrated PV modules for the first time. The so called Swiss PV Wall System (SPWS) contains all elements needed in the façade, behind the PV modules with a power of 1 kWp, like a PV inverter, a heat pump and a hot water tank. Simulation showed that virtually 100% of the PV energy can be used either by the heat pump to produce hot-water or the household’s electricity needs. A functional model of the SPWS was realized and first measurements showed that the heat demand of a one family household may be covered for the majority of the months during the year. Economic analyses showed that the cost per kWh heat is at about 0.215 CHF and thus lower than standard solar thermal and some fossil solutions.

31st European Photovoltaic Solar Energy Conference and Exhibition; 2037-2041, Bifacial solar modules promise an increased energy yield, compared to systems with standard, monofacial panels, and also offer new opportunities with regard to the installation. One particular approach is the vertical mounting of PV modules, which is reported to be an effective measure to avoid soiling or dust deposition and is an option to obtain a broadened energy generation profile. In spite of the general interest in this type of installation, the amount of published data is very limited, especially with regard to arrays, for which pronounced shading effects can be expected. In this work we present an analysis of the energy yield and the respective losses for arrays of vertically mounted bifacial solar modules with varied installation conditions.

29th European Photovoltaic Solar Energy Conference and Exhibition; 3248-3250, There is an increased energy yield for n-type bifacial solar modules as compared with n-type monofacial modules. However, the benefit of bifaciality depends on several factors, such as module height, ground reflectivity, distance between modules, etc. This work enriches the understanding of the correlation between laboratory measurements and outdoor performance of bifacial modules. Indoor measurements of monofacial and bifacial modules, containing n-type bifacial cells of similar technology, were performed at PI Berlin (Germany). Their outdoor performance was monitored in El Gouna (Egypt), where the yield in terms of Wh/Wp was compared, and in Winterthur (Switzerland), where the influence of module height and ground reflectivity was studied. In El Gouna, an average yield gain of 22.3% in terms of Wh/Wp was measured for a bifacial module as compared with a monofacial module, over the first eight months of 2014. A maximum average monthly gain of 25.6% was reached in the month of August. A peak power output of 426 W was registered. In Winterthur, the application of a white foil beneath a bifacial module showed a gain of 7.6% in power output divided by the incident irradiance on the front side, as compared with a gravel covered ground. The power/irradiance gain was 9.7% when the module was raised from 0 cm to 64 cm above the ground level.

29th European Photovoltaic Solar Energy Conference and Exhibition; 612-616, In this paper, we present the InPERC technology implemented into a multi- and monocrystalline silicon (mc- and Cz-Si) solar cell production of major Asian cell manufacturers. Stable average efficiencies over 18% and 20 % were demonstrated, respectively. Best average efficiencies of 18.4% were achieved on mc-Si solar cells with a best cell efficiency of 18.8%. To reduce the cost of ownership (CoO) of the InPERC upgrade, the annealing step after ALD of Al2O3 was successfully skipped by integrating it into the direct tube PECVD without increase of PECVD process time. Furthermore, the Al2O3 thickness was reduced to 4 nm and the etch removal for rear side smoothening to 2 μm without loss in efficiency. An InPERC module passed all applied accelerated ageing tests (five times humidity freeze, damp heat, PID-test). In a CoO-comparison of different PERC routes, the InPERC technology showed the lowest total CoO and the lowest payback period of all investigated PERC candidates.

28th European Photovoltaic Solar Energy Conference and Exhibition; 1861-1866, In this paper, we present results of the implementation of the InPERC technology into an industrial pilot production of a major Chinese cell manufacturer. The process sequence utilizes all production equipment of the standard production line for screen printed full area Al+BSF solar cells. In addition, the rear surface is smoothened. For this purpose, the hardware of one existing standard InOxSide for wet chemical edge isolation is upgraded to InOxSide + without changing the footprint of the tool. The rear side is passivated using SoLayTec’s InPassion ALD mass production machine for ultrafast spatial atomic layer deposition (ALD) of Al2O3. The SiNx capping layer is deposited using standard PECVD equipment of the existing production line. Furthermore, a laser is used to open the rear side contacts prior to screen printing the metallization. In a first step, the InPERC ALD technology was developed on CZ+Si 156 x 156 mm² wafers at RENA. Average cell efficiencies of 19.5% were achieved with screen+printed metallization and without selective emitters: an increase of about 1%abs compared to our full Al+BSF baseline of about 18.5%. It was found that a surface smoothening by removal of about 4 μm is sufficient to reach implied Voc values of over 700 mV and 680 mV for CZ+Si and mc+Si material, respectively. This leads to an efficiency gain of up to 0.5%abs due to surface smoothening. The passivation quality of the layer stack is significantly improved by an annealing step after the ALD process. It was successfully shown that by using an optimized recipe for the PECVD process of the capping layer this post deposition anneal (PDA) can be skipped. Thus, the full potential of the excellent passivation quality of ALD Al2O3 can be obtained at lowest cost of ownership. It was found, that – by use of a suited laser and aluminum paste – damage to the silicon by the laser ablation can be healed effectively by a deep formation of the local Al+BSF. The full potential of the InPERC technology was demonstrated at RENA with direct Ni/Ag plating as front side metallization and FireFOXTM as front passivation. A best efficiency of 20.3% was achieved. The InPERC ALD technology on CZ+Si was transferred to a mc+Si industrial pilot production of a major Chinese cell manufacturer. It was found that an Al2O3 layer thickness of 7 nm and even 4 nm could be applied without loss in efficiency, further reducing cost of ownership. On mc+Si material efficiency gains of about 0.6%abs were demonstrated. Top average efficiencies of 18.0% could already be achieved up to now without a selective emitter.

28th European Photovoltaic Solar Energy Conference and Exhibition; 1374-1379, In this paper, RENA presents progress in developing a metallization scheme for silicon solar cells based on laser ablation and direct plating of Ni/Ag or Ni/Cu/Ag on silicon. A cluster consisting of a laser ablation tool, an inline plating sequence for NiCuAg or NiAg followed by an annealing furnace can be upgraded in conventional solar cell lines with screen printed front contacts replacing the front side print. Solar cell batches processed with the RENA NiAg metallization scheme yielded average efficiencies of 19.4% in an industrial environment on fully automated mass production tools capable of a throughput of 1200 wph. This corresponded to an efficiency increase of about 0.5% compared to the screen printed baseline. However, this metallization technology requires reliable module integration. Modules with conductive adhesives used for interconnection had been already successfully demonstrated. This work concentrates on a number of interconnection approaches for direct plated metal contacts including soldering interconnectors directly to plated busbars or alternatively to printed busbars. Furthermore, first results from smart wire interconnection are shown. Plating has been successfully applied to Al BSF solar cells, to PERC-type solar cells and to MWT solar cells and is seen as an enabling technology for future solar cell generations.

28th European Photovoltaic Solar Energy Conference and Exhibition; 1761-1764, The presented study provides a detailed insight into solar cell processing of diamond cut (FASW) silicon wafers. Fundamental investigations solidify the demand for matching adaptions of sawing, cleaning and texturing techniques. Basic evaluations are conducted by analysis of produced sawing marks, cleaning steps for as-cut silicon surfaces, texturing homogeneity and comparison of surface reflectance. The impact on solar cell performance is discussed and interpreted with respect to overall processing sequences.

28th European Photovoltaic Solar Energy Conference and Exhibition; 1080-1084, This work investigates the integration of a wet chemical single-side emitter etching process into the process sequence of screen printed p-type Czochralski-grown silicon MWT-BSF (metal wrap through aluminum back surface field) solar cells. The MWT-BSF solar cells fabricated with single-side emitter etch back achieve a median conversion efficiency of 18.4 % (as processed), while MWT-BSF solar cells isolated by laser grooves show a slightly lower median conversion efficiency of 18.2 % (as processed). Repeated current-voltage (I-V) measurements under forward and reverse bias using stabilized MWT-BSF solar cells with single-side emitter etch back confirm that a novel via paste enables stable results under forward bias (standard operation mode), although the via paste is in direct contact with the p-type base. MWT-BSF solar cells with single-side emitter etch back show increasing current densities under reverse bias without affecting the cell performance after repeated I-V measurements, this behaviour could be used for an integrated bypass approach. The results confirm the successful integration of single-side emitter etch back into the MWT-BSF process sequence allowing for the reduction of the process sequence by one process step compared to MWT-BSF solar cells isolated by laser grooves.

27th European Photovoltaic Solar Energy Conference and Exhibition; 561-566, In this work we study the impact of chemical polishing on the performance of mono-crystalline PERC cells. Starting from random pyramid textured surfaces, the rear side polishing step is performed by means of an inline single-side wet-etch tool. The influence of the pyramid smoothening on light trapping, surface recombination and contact formation is here studied separately. We conclude from our analysis that a moderate smoothening, corresponding to around 5-6 μm Si etch, is required in order to maximize the cell performance and that, on the other hand, a complete planarization of the rear surface can be detrimental, besides being cost un-effective. While the surface recombination generally benefits from a flat rear surface, light absorption and contact formation are more effective when roughness Ra is in the range between 300-500 nm. Contact formation is also influenced by the roughness because mass exchange between Al and Si takes place all over the rear side surface. On large area industrial PERC cells with Ag screen printed contacts we achieve a best cell efficiency of 20.1% with 6 μm of Si polishing removal and 19.9% with only 3 μm of Si removal. In the latter case the total Si consumption, including saw damage removal and texturing, is lower than 20 μm per cell.

27th European Photovoltaic Solar Energy Conference and Exhibition; 1563-1565, In this paper, we present results of the development of a selective emitter structure for crystalline silicon solar cells suitable for industrial mass production. The process sequence follows the approach first introduced by Volk et al [1]. Laser doping is performed directly after emitter diffusion. In a second step, the emitter is etched back homogenously without a mask to improve the emitter quality and remove the dead layer. While the resulting selective emitter yields a higher efficiency potential than with laser doping alone, the simplicity of the homogenous etch back step, results in a lower invest and COO than a “Mask and Etch Back” approach. On life time samples the processes of emitter diffusion, laser doping and emitter etch back were thoroughly studied. Development was performed on industrial production equipment in preparation for a transfer of this technology to mass production. The optimization of the selective emitter on 156 mm cz-solar cells yielded an average efficiency of 18,60 %, which corresponded to an efficiency gain of 0,3% compared to our baseline.

27th European Photovoltaic Solar Energy Conference and Exhibition; 766-771, The presented study provides a detailed insight for wet chemical texturing procedures of “cast-mono” or “mono-like” silicon substrates. Fundamental investigations establish the demand for adapted etching techniques in order to address the exceptional “cast-mono” surface properties. Fundamental evaluation parameters are texturing homogeneity, magnitude of effective surface reflectance and quality of produced texturing structures. The impact on solar cell characteristics, relevant processing steps and industrial application is discussed and interpreted with respect to material classifications and cost-effective manufacturing sequences.

26th European Photovoltaic Solar Energy Conference and Exhibition; 1199-1202, In the last months, Ag price has skyrocketed so that saving Ag has now a similar priority than increasing the conversion efficiency of silicon wafer solar cells. In this paper we present the current status quo of screen-printed solar cells in terms of Ag cost contribution and point out different ways to reduce this factor. Special focus is directed onto direct plating Ni-Ag on laser-opened Si which allows for a strong decrease in Ag consumption. An experimental study with industrial multicrystalline precursors shows that plating to the maximum efficiency is not the best economic choice and that increasing the finger number and plating less metal is an effective measure to decrease Ag cost. We can show that the main interest in laser-opening and direct plating is the saving of Ag, the associated increase in efficiency is welcome but not mandatory for cost effectiveness.

26th European Photovoltaic Solar Energy Conference and Exhibition; 1659-1661, The implementation of the selective emitter technology is one of the most attractive changes for industrial solar cell manufacturing. In this paper the pretreatment prior to light induced plating of thin electrodeposited Nickel seed layers and subsequent electrodeposited Silver has been studied. The cell results have been analyzed in terms of ghost-plating, contact resistance of the Silicon/Nickel interface and shunting behavior depending on the used pretreatment solution. Conclusion: An influence was observed using different pretreatment solutions prior to nickel plating concerning ghost-plating, contact resistance and adhesion of the plated solar cell. The best cell results processed so far on multi crystalline silicon solar cells without ghost-plating reached an efficiency of 17.5% on industrial production compatible processes.

25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion, 6-10 September 2010, Valencia, Spain; 1896-1898, There are different technologies available for selective emitter (SE) formation for crystalline silicon wafer solar cells. While conventional approaches combine SE with screen-printing, Laser Chemical Processing (LCP) uses subsequent direct light-induced plating (LIP) to fully exploit the efficiency potential of Al-BSF solar cells. Using screen-printing instead of LIP with SE lowers the expected efficiency gain by at least a factor of 2. Thus SE technologies are sought that enable subsequent LIP. LCP offers fully flexibility for LIP as well as screen-printing metallization. This paper summarized the status of LCP + Ni-Ag-LIP processes. High efficiencies around 19% on mono Si are reached with large process windows for the LCP process. Also, first modules have been manufactured to demonstrate sufficient adhesion for module integration.

25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion, 6-10 September 2010, Valencia, Spain; 1475-1478, We present novel methods for texturing and metallizing silicon-wafer based solar cells. The texturing method forms a hexagonal array of pits on the surface resulting in a honeycomb texture. This is achieved through the addition of a new patterning machine prior to a modified wet etching step. The texturing used does not rely on saw damage for initiation, and thus is compatible with any method of ingot sawing or kerfless wafer formation. It is also compatible wafers/grains of any crystallographic orientation. Reflectivity is lower than that achieved by the industry-standard isotexture for multicrystalline wafers. Narrow grooves can be formed simultaneously with the honeycomb texture to enable an advanced front metallization technique while the back can be polished for rear dielectric passivation. A novel method allows the self-aligned dispensing of materials into these grooves. Following SiNx deposition, silver paste is dispensed into the grooves, and this thin seed layer is co-fired along with the back metallization. This seed layer can be plated up with either Ag or Ni/Cu/Sn to form fingers 7 microns in height to enable a reduction in resistive and shading losses compared to screen printing. Low contact resistivities of < 2 milliohm-cm2 have been achieved on uniform and very shallow emitters ~ 90 ohms/sq with a Ag seed layer and plate-up of Ag, thus enabling further improvements in Voc, Jsc, and FF. Large-area, encapsulated multicrystalline cells have been made with efficiencies close to 18% by these techniques. Phosphorus dopant also can be dispensed into the grooves to enable a simple selective emitter structure which results in no undesired band of deep emitter extending to either side of the fingers. 1366 Technologies is currently scaling up patterning and dispensing while RENA is scaling up wet etching and plating.

25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion, 6-10 September 2010, Valencia, Spain; 2183-2185, The current trend in solar cell manufacturing is the implementation of a selective emitter to a standard solar cell. A very high locally phosphorous doped emitter underneath the contacts is combined with a high sheet resistance with low auger recombination at the illuminated area. An additional efficiency increase can be achieved by good contact formation and high line conductivity of Light Induced Plated (LIP) contacts. In this paper the important aspects of the direct plating technology for industrial production are summarized; details on the metal layer systems Ni/Ag and Ni/Cu/Ag are shown.

24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany; 1356-1359, Wet chemical processes represent an important part of the value chain in the production process of crystalline silicon wafers and solar cells. The paper gives an overview of the state of the art technology of wet chemical processes in crystalline silicon wafer and solar cell production, such as wafer cleaning, texturing, high purity cleaning, oxide removal, single side etching and additional processes like laser chemical doping combined with plating are presented briefly.

24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany; 1855-1859, We developed and evaluated a wet-chemical etching process to continuously remove thin layers from the emitter after P-diffusion. In combination with in-line diffusion this emitter etch-back can improve efficiency of silicon solar cells significantly. This is caused by an increased blue response through reduced dead layer. The etching is highly homogeneous and controllable and can be integrated easily in standard cell production lines. The process exhibits a distinct optimum for efficiency against etching time. In that region, the increase in efficiency can be as much as 0.7% abs. compared to the non-etched samples and the in-line-diffused cells are on a par with cells made by standard POCl3 diffusion.

24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany; 282-284, The front grid of screen printed solar cells strongly limits the efficiency in terms of shading and resistive losses. Main focus of this work was to provide an alternative two-step front contact process consisting of fine printing followed by an adapted plating stack of Ni/Cu/Sn. Results on improved fine line printing as well as a new plating technique will be presented for the first time. Optimized parameters for printing with newly developed techniques as well as adapted plating techniques will be shown. Solar cells using the new developed front metallization have been characterized and compared with standard screen printed solar cells. Efficiency gain of more than 0.4% has been achieved so far.

24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany; 1712-1714, The sequence of laser chemical processing (LCP) and electrochemical metal deposition direct on silicon is presented as the next generation of front grid metallization. The subsequent metallization process after selective emitter forming works self aligned and shows structures with line width as thin as ~40 μm. Simulations give confidence that efficiency improvements in the range of 1% are achievable as compared to industrial screen printed solar cells. To reach best contact resistance first nickel was plated on locally high doped areas which were produced by LCP method. This layer is followed by thick by silver plating. If thickening is done by copper the prior nickel also needs to built up to serves as a diffusion barrier. Only copper as a strong cost reducing process (-70% compared to pure silver) needs a third metal layer like tin or thin silver to achieve a solderable surface finishing. Both sequences were applied to produce high efficient solar cells with a new front grid metallization cluster without using printing methods. All presented plating processes were carried out on a industrial production platform which ensures a single side wet chemical treatment.

24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany; 1748-1750, In industrial production of mono crystalline solar cells alkaline texturing is nowadays a standard process. The most used process in industry is the KOH (or NaOH) / IPA process. In due to the small process window is for most wafer qualities a different recipe needed. Here a new innovative alkaline texturing process for cz silicon wafers is presented. The texturing solutions contains a new additive, named AlkaTex Plus. With this new process most wafer qualities from different suppliers could be textured with the same recipe. In comparison to the standard process the chemical consumption sinks. With a process time of 20 to 30 min the output could be increased. With this new ESH compliant additive a typical pyramid size of 2 – 5 μm could be achieved.