Beam Shaping for High Throughput Laser Doped Selective Emitter Solar Cells

To overcome limitations in efficiency originating from the front side of a crystalline silicon solar cell, the concept of the selective emitter has been investigated in recent years. Several approaches have been presented and tested for their industrial feasibility. Although almost all concepts are able to achieve a gain in conversion efficiency, not all technologies are realizable due to process complexity and possible major modifications necessary for retrofitting existing production lines. This motivates a simple process flow for the fabrication of a selective emitter structure. Laser Doping from phosphorous silicate glass (PSG) is a cost attractive approach, as only one additional processing step is required for selective emitter formation and no consumables are used. In this work solar cells on both mono- and multicrystalline silicon with selective emitter have been fabricated. A beam splitter in conjunction with a high power laser system has been used to allow for high throughput processing with 10 parallel laser beams. Solar cell parameters are shown and discussed. To investigate possible hot spots under reverse bias conditions of the shallow emitter, Dark Lock-In Thermography (DLIT) measurements have been conducted and reveal no hot-spots.