Large-area p-type HIP-MWT silicon solar cells with screen printed contacts exceeding 20% efficiency

physica status solidi (RRL) - Rapid Research Letters (Impact Factor: 2.39). 01/2011; 5:286-8. DOI: 10.1002/pssr.201105311

ABSTRACT The MWT-PERC (metal wrap through passivated emitter and rear cell) concept introduced in 2006 [1, 2] combines the advantages of surface passivation [3] and the metal wrap through approach [4], resulting in an increased conversion efficiency. However, due to the required structuring of the emitter on the rear side, the process sequence is rather complex. Our simplified structure for passivated MWT solar cells, called HIP-MWT (high-performance metal wrap through), maintains the gain in efficiency while reducing the process complexity to a minimum. The simplified structure omits the formation of an emitter region on the rear surface. Therefore no structuring steps are required. Within this work, we present solar cells based on the simplified HIP-MWT structure and non-simplified MWT-PERC reference cells. The cells of both concepts are processed in parallel to enable a direct comparison.

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    ABSTRACT: This work investigates sintered, screen-printed silver contacts on lowly doped p-type silicon with different intermediate dielectric layer systems using scanning electron microscopy and dark current-voltage measurements. The data reveal electron tunneling through a thin insulating layer as the most probable transport mechanism. A model based on Fowler-Nordheim and direct tunneling is presented that allows for the description of reverse current-voltage characteristics and the extraction of effective contact properties. The investigated screen-printed metal insulator semiconductor structures are proposed as solar cell integrated bypass that reduces the risk of hot spot generation and power loss during partial shading of a module. Furthermore, the integrated bypass approach enables the fabrication of solar cells from silicon material that tends to show early breakdown of the p-n-junction.
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    ABSTRACT: The development of cost-effective and highly efficient solar cells is a primary goal of current research activities. In this work we investigate two different metallization concepts based on screen-printing technology that are aimed at achieving increased cell conversion efficiency of p-type silicon metal-wrap-through (MWT) solar cell structures. The first approach is the reduction of the pad area of the external rear n-type contacts. Furthermore a multilayer metallization concept is presented that allows for the decoupling of the rear external n-type contact and the p-type silicon base. In this context new pastes for via metallization are investigated—namely low-temperature silver–polymer pastes. The second approach is the optimization of the metallization layout of MWT solar cells to minimize cost of ownership. Therefore the number of contact rows, the finger width, and the number of n-type contact pads per contact row are varied methodically by using analytical simulations. The results are compared with experimental data. Both approaches show a potential for a further conversion efficiency increase of p-type silicon MWT solar cells.
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