Screen printed metal contacts to Si solar cells — Formation and synergistic improvements
Silicon solar cell technology has advanced by improvements to all aspects of cell design including metallization. Improvements to metal contacts have been synergistic with other cell improvements such as passivation, lightly doped emitters, and boron doped emitters. This paper briefly recounts the history of c-Si PV metallization technology and its synergy with other cell technologies. It concludes with a perspective on various metal contact mechanisms.
Optimizing Fine Line Dispensed Contact Grids
Abstract Previous studies on dispensing as an alternative front side metallization process in crystalline silicon photovoltaics demonstrated, how an adaption of paste rheology allows for a precise adjustment of contact finger geometry in a wide range. In order to demonstrate the benefit of this advantage, the analytical simulation tool Gridmaster was extended to observe the effect of various geometrical parameters on solar cell results and manufacturing costs. In addition, respective geometrical parameters of thick film printed contact fingers were determined using a special in house developed tool based on MATLAB. As a result, contact geometries as achievable by means of ultrafine line dispensing are ideally suited for contacting silicon solar cells. Compared with standard fine line single screen printed finger geometries, an efficiency increase of up to Δη = 0.4%abs. as well as a reduction of manufacturing costs of 1 €ct./W p on module level can be achieved using dispensing technology. In order to obtain suitable data, simulation results were compared with solar cell results on industrial pre-processed Cz-Si p-type wafer material applying the novel ten nozzle parallel fine line dispensing unit. Therefore, a new dispensing paste was developed combining optimum optical finger aspect ratios of AR o =0.7 with excellent contacting behavior. A successful first test of applicability already led to a maximum cell efficiency of η = 18.7%, demonstrated on an industrial emitter with a sheet resistance of around R sh  = 90 Ω/sq.
Analysis of silver thick-film contact formation on industrial silicon solar cells
The silver thick-film contact is the most widely used front side contact for industrial silicon solar cells. The objective of the presented investigations was to improve the understanding of front side contact formation by varying the contact firing process. We therefore introduced an additional temperature plateau in the cooling zone. The firing process was assessed based on the results of the IV characteristic. Fill factor, series resistance and open circuit voltage were the main values taken into consideration. Additionally we earned out specific contact resistance and Corescan measurements. The performance of the solar cells was characterized by spectrally resolved internal quantum efficiency measurements and thermographic measurements. The results were correlated with the variations of the contact firing and are discussed referring to the different models of the current transport mechanism in thick-film contacts.