Impact of the Presence of Busbars During the Fast Firing Process on Contact Resistances

P‐Type Silicon Solar Cells with Passivating Rear Contact Formed by LPCVD p+ Polysilicon and Screen Printed Ag Metallization

“…TLM measurements of the 0BB cells show the same trend, but with a significantly lower ρ c,rear down to 2.7 mΩcm 2 at T set = 880 °C, which is also highlighted by an around 0.3 Ωcm 2 lower R s than 5BB cells, see Table . This finding is in agreement with literature data for boron diffused emitters, which have been contacted by screen printed Ag pastes using a busbar‐free layout, and which has been described earlier by a short‐circuit effect of the busbar during contact formation . Thus, to achieve a low R s , either the amount of fingers on the rear side needs to be increased and/or a 0BB design should be used, to compensate for a high ρ c of the screen printed Ag paste.…”

Laser-Powered Co-Firing Process for Highly Efficient Si Solar Cells

“…On the contrary, the trailing parts do not have that time, leading to bad contact formation and lower EL signal. Following the example of Chu et al [16], the replacement of the H-pattern grid by a busbar-less grid with the fingers fired perpendicularly to the transport direction does lead to a higher EL signal at the trailing cell parts being at the same level as for the heading cell parts [see Fig. 4(d)], being comparable to the positive effect observed in [16].…”

“…We believe that this EL pattern might stem from the "short-circuit effect" described by Kim et al [15]: direct ("short-circuited") Si-Ag(bulk) connections that supposedly cause a lack of emitter electrons leading to fewer Ag crystallites and an effectively underfired contact. These "Ag-Si short-circuits" form locally and nonuniformly, and are caused by non-uniformities, such as the locally time-shifted wafer heating in transport direction (see Section III-A) and the resulting time-shifted contact formation process [16], [17]. These "Ag-Si short-circuits" supposedly only affect grid parts which are connected to these spots, but not parts which are disconnected.…”

“…Following the example of Chu et al [16], the replacement of the H-pattern grid by a busbar-less grid with the fingers fired perpendicularly to the transport direction does lead to a higher EL signal at the trailing cell parts being at the same level as for the heading cell parts [see Fig. 4(d)], being comparable to the positive effect observed in [16]. This suggests a significant reduction of the short-circuit effect to a negligible level.…”

Project “FEUERDRACHE”: Process development and control of contact firing processes for high-efficiency silicon solar cells

“…To prevent the SC-effect from affecting the performance of the solar cell, areas on the cell that have a temperature difference at a certain time point, must not be connected by the metallization on the front side. This was demonstrated by Chu et al [13] using a front side metallization pattern without busbars and processing the cells with front side fingers perpendicularly aligned to the transport direction, the suspected effect becomes negligible. In this case, the efficiencies of the cells are only 0.1%abs lower than the ones fired with the classic technology.…”