Low-temperature sintering properties of the screen-printed silver paste for a-Si:H/c-Si heterojunction solar cells

For a-Si:H/c-Si heterojunction (SHJ) solar cells, low-temperature sintered silver paste is necessary to fabricate the metal electrodes on transparent conductive oxide layer. Here, the thermal characteristic, the conductivity, the adhesion strength on indium tin oxide substrate and the microstructure evolution of the screen-printed low-temperature sintered silver grid were investigated by varying the sintering temperature and the sintering time. The results show that the grid performance is closely related to its microstructure. A relatively high sintering temperature and a long sintering time are beneficial to make the organics in the Ag paste burn out and the adjacent Ag particles coalesce together to be larger ones. As a result, the Ag grid can get a dense microstructure and tightly adhere onto the substrate surface. Thus, low line and contact resistance is achieved. What is more, the evolution of the preferential orientation of Ag particles has some contributions to the improved grid conductivity. Specifically, for the SHJ solar cell fabrication, in order to be compatible with the low-temperature deposition of a-Si:H, a long sintering time larger than 60 min with the sintering temperature in the range of 200–230 °C is preferred to realize high performance Ag electrical contacts.