Analysis of silver thick-film contact formation on industrial silicon solar cells

Abstract

The silver thick-film contact is the most widely used front side contact for industrial silicon solar cells [1]. 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 carried 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

Physical understanding of the behavior of silver thick-film contacts on n-type silicon under annealing conditions

“…Lead exists as precipitates on the bottom side of the finger [20] and in the glass [23]. Current flows from the silicon via the silver crystals [24]. This is indicated by red arrows for the left crystal in Fig.…”

“…Three main current paths exist from the silver crystals to the silver bulk. Current flows via a direct contact between crystal and silver (left crystal) [24], through a very thin (o10 nm) glass layer by tunneling (middle crystal) [25] or by multi-step tunneling via lead precipitates (right crystal) [23]. Other current paths are unlikely as the glass layer is insulating [26].…”

Numerical Simulation Analysis of Ag Crystallite Effects on Interface of Front Metal and Silicon in the PERC Solar Cell

“…All samples were printed and subjected to a high-temperature firing process at three different temperatures: 850, which is the standard temperature, 900 and 950 • C. The samples with different firing temperatures were used to investigate the firing temperature effects on the Ag crystallite distribution and J 0.metal values. It is noted that our firing temperature has to be higher than 800 • C due to the fact that the lower firing temperature cannot appropriately form the electrically connected Ag electrode on the emitter region in silicon [18]. The diagram for the process of both samples is shown in Figure 1b.…”

Detailed analysis of annealing silver front side contacts on silicon solar cells

“…This might have affected the conductivity of the finger and thus increased the series resistance. Figure 4b reveals that silver crystallites [1,[8][9][10][11] at the interface between the silver finger and the silicon bulk have the shape of a pyramid before annealing but tend to be lenticular after annealing. This is confirmed by the SEM images in figures 4c and 4d where the imprints of the pyramid on the silicon surface are shown.…”