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33rd European Photovoltaic Solar Energy Conference and Exhibition; 362-367, This paper presents results of combining two promising future technologies: i) metal catalyzed textured (MCT) diamond-wire sawn (DWS) mc-Si wafers and ii) nickel-copper-silver (Ni/Cu/Ag) plated front contact processing. Results of optimizations of laser patterning, annealing and module string soldering are presented. Several 60-cell module with a power output of around 270 W were made, followed by subsequent module reliability testing. All module tests have been passed within the existing boundaries. Pseudo fill-factor (pFF) and open circuit voltage Voc have been identified as the parameters with the highest potential for further improvements. First successful results of plating-emitter development on a MCT-surface are presented.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 796-800, The intention of this work is to show the advantages of the Ni/Cu/Ag plating process when the number of busbars on the solar cell is increased. Cells with four and five busbars were processed and compared to those with three in respect of efficiency, finger and solder adhesion. Simulations to calculate the metal reduction and the experimental values are compared. Estimations how much the production costs may be reduced are shown.

31st European Photovoltaic Solar Energy Conference and Exhibition; 372-376, In this work we report on progress in applying plating technology as alternative high throughput low cost metallization technology for advanced c-Si solar cells. Front contacts are formed by light assisted single sided plating of Ni and Cu to areas that had been selectively laser ablated on homogeneous emitter regions covered by PECVD SiNx:H. A large set of p-type Al-BSF solar cells with plated Cu based contacts were integrated into conventional PV modules and reliability has been assessed according to the IEC61215 standard. Remarkable median FF values exceeding 80.7% have been achieved on moderately doped homogeneous emitters with a P surface concentration below 4·1019 P/cm3. The solar cell performance parameters have narrow distributions. The modules successfully pass reliability testing.

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; 1220-1224, Passivated Emitter and Rear Cell (PERC) solar cell concept is one of the most promising technology for increasing crystalline silicon solar cell efficiency as well as a technology at relatively low production costs compared to other advanced solar cell concepts. Among the different candidates of materials for the passivation of the rear side, aluminum oxide (Al2O3) deposited by spatial atomic layer deposition (ALD) is very attractive due to its excellent passivation properties and its high processing throughput. In this work, we investigate the influence of the post-deposition thermal treatment of spatial ALD Al2O3 on the passivation properties of the Al2O3/SiNx stack system. It is shown that for an ALD Al2O3 layer thickness of 10 nm, a sufficient high annealing temperature is necessary to prevent blistering and to achieve excellent passivation, which has been investigated for two SiNx deposition methods: remote and direct plasma enhanced chemical vapor deposition (PECVD). Furthermore, it has been investigated that in the case of using thinner ALD Al2O3 layers down to 6 nm as well as by adapting the SiNx recipe of the direct plasma, the post-deposition anneal can be avoided, which is beneficial for further down scaling of the production costs of the PERC solar cell.

25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion, 6-10 September 2010, Valencia, Spain; 1810-1815, Intrinsic hydrogenated amorphous silicon a-Si:H(i) offers a very good passivation quality. Adding dopants to the deposition reduces the passivation quality. However, sufficient doping is needed to build the p-n-junction which is essential to gain an actual voltage. Furthermore, the conductivity of the a-Si:H is also a function of the dopant concentration. Poor conductivities in the emitter layer causes high series resistances, limiting fill factor and cell efficiency. To achieve good passivation quality, sufficient band bending and low resistivity simultaneously, we have introduced a new approach of applying a doping profile to the deposition of the amorphous emitter layer. The conventional concept to process silicon heterojunction (SHJ) solar cells is to deposit a heavily doped a:Si-H(n or p) layer on a thin intrinsic one. In this paper we will compare structures with gradually doped emitter profiles to conventional ones. Gradually doped emitters are processed in one single deposition step, which offers simple and fast processing. The total electrical conductivity can be increased by a well chosen doping profile. This is shown by simulations based on conductivity measurements and full heterojunction solar cells. The best n-type, FZ wafer heterojunction solar cell realized within this first investigation has an efficiency of 18.9%.

25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion, 6-10 September 2010, Valencia, Spain; 1820-1824, Comparison of the open-circuit voltage Voc determined by sunsVoc to the implied voltage Voc,impl determined by transient QSSPC lifetime measurements can lead to a quick and easy analysis and characterization of silicon heterojunction (SHJ) solar cells, especially in regard to finding the optimum doping concentration of the emitter layer (stack system). The Voc,impl represents the interface passivation quality. The sunsVoc value gives us additionally a measure of the apparent band-bending. Increasing the concentration of doping gases during the deposition of e.g. a-Si:H(p) reduces the interface passivation quality (Voc,impl) and increases the band-bending (sunsVoc value). The best trade off is realized when the ratio of sunsVoc to Voc,impl (Voc trade off ) first comes to a saturation value near 1, while increasing the doping concentration. For a-Si:H(p) layers the pseudo fill factor PFF is found to be dependent on the doping concentration, too. Thus, the maximum value obtained for the PFF sunsVoc product is taken as a measure for the optimal doping concentration of a-Si:H(p) emitter layers. This approaches are applied to answer the following questions: i) what is the optimum doping concentration for an a-Si:H(n) emitter layer vs. an a-Si:H(i & n) emitter layer stack? ii) what is the best doping concentration of the a-Si:H(p) layer in an a- Si:H(i & p) emitter layer stack system including a variation of the a-Si:H(i) as well as the a-Si:H(p) layer thickness?

24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany; 1580-1585, This work tackles the question whether a soft PECVD-deposition of intrinsic, hydrogenised, amorphous silicon (a-Si:H(i)) is really supportive for the passivation quality of the heterojunction interface between a crystalline wafer and the a-Si:H(i)-layer itself. Two PECVD-deposition methods are under investigation: i) parallel plate 13.5 MHz deposition chamber (PP-13.5 MHz), and ii) an inductively coupled plasma deposition chamber (ICP). The time dependent degradation and the thickness dependence of the passivation quality of the a-Si:H(i)- layers are discussed as an important fact to note, when the work aims to compare different a-Si:H(i)-layer deposition techniques and/or deposition parameter sets. The two different PECVD a-Si:H(i) deposition techniques are optimized and compared with the goal to find the highest possible passivation quality while reducing the layer thickness below 10 nm.

23rd European Photovoltaic Solar Energy Conference and Exhibition, 1-5 September 2008, Valencia, Spain; 1720-1723, We investigated different amorphous SixC1-x:H layers for their applicability as hetero-emitter materials. The deposition with Plasma Enhanced Chemical Vapour Deposition (PECVD) in a preliminary industrial stage plasma reactor was done without any wet-chemical pre-cleaning directly before the deposition. In a first step the single layers were characterised optically with Spectral Ellipsometry (SE) which showed an enhanced transparency of a-SixC1-x:H layers with a very low carbon content below 10 % compared to a-Si:H. On both sides passivated Si float zone wafers we measured minority carrier lifetimes with the Quasi Steady-State Photoconductance (QSS-PC) method which showed excellent passivation performance for 70 nm thick layers and a detrimental performance loss for thicknesses below 10 nm. With the Constant Photocurrent Method (CPM) we found a significant increase of the Urbach energy when incorporating phosphorous into the layer network. The solar cell had a hetero-junction on the front-side and a passivated rear-side (SiO2) with local contacts (PERC). The first cell batches were strongly influenced by technological problems such as material inhomogeneities over the cell area, contaminations on the surface and a poor grid finger/ITO adhesion behaviour. Nevertheless, we could achieve an excellent open circuit voltage of 674 mV.

23rd European Photovoltaic Solar Energy Conference and Exhibition, 1-5 September 2008, Valencia, Spain; 1149-1152, We report use of heavily doped polysilicon combined with a tunnel dielectric to provide an alternate to diffused junctions for silicon solar cells. Thin tunnel dielectrics (6-12Å) are fabricated using methods adapted from IC processing. These serve as diffusion barriers and passivation layers. When combined with heavily doped polysilicon, they can form an ideal step junction with interface passivation, enabling low dark currents not possible with diffused emitters. We show that it is possible to obtain hyper-abrupt junctions with the tunnel layer providing interface passivation, and that these junctions obtain a VOC of 676 mV on 780 μm thick substrates.

23rd European Photovoltaic Solar Energy Conference and Exhibition, 1-5 September 2008, Valencia, Spain; 1023-1028, In this work we focus on the surface passivation of p-FZ, 1 Ωcm silicon wafers by intrinsic, silicon-rich, amorphous silicon carbide (a-SixC1-x:H) with excellent passivation quality (Seff < 5 cms-1 for p- and n-type 1 Ωcm silicon at n=5·1014 cm-3). For the purpose of extracting the effective surface recombination velocity (Seff) independent of the bulk properties, we use a set of identically passivated wafers of different substrate thickness (W). The injection-dependent carrier lifetime eff(n) is determined in a wide injection level range (1010-1017 cm-3) using a combination of the quasi-steady-state photoconductance (QSS-PC) and photoluminescence (QSS-PL) technique. Seff is extracted by evaluation of the slope of the 1/eff vs. 1/W plot for each injection level without any additional assumptions on the bulk lifetime. These pure Seff data obtained in such a way is then used within the simple Shockley-Read-Hall (SRH) model to extract surface parameters such as the interface charge density Qf. Surface photovoltage measurements (SPV) performed on the a-SiC/c-Si system confirm an amphoteric behaviour of the interface charge. Our study shows that the low-injection lifetime data determined by QSS-PL plays a crucial role for the accurate modelling of surface parameters.