Search

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; 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; 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.