Laser Transfer and Firing of NiV Seed Layer for the Metallization of Silicon Heterojunction Solar Cells by Cu-Plating

Abstract

We present a laser-based method for the metallization of silicon heterojunction solar cells by Cu-plating. It consists of first applying a dielectric layer on the transparent conductive oxide (TCO) as a plating mask. Then, a NiV seed is transferred by laser induced forward transfer (LIFT) from a plastic carrier foil onto the wafer. In the second laser step, the NiV layer is fired through the dielectric layer to form a contact to the TCO. After the laser process, Cu-fingers are produced by plating. The dielectric plating mask remains on the cell. Parasitic plating is prevented by using an advanced reverse pulse plating process. With the first solar cells we reach a maximum efficiency of 22.2% and an efficiency gain of 0.5% abs compared to lowtemperature screen printing reference cells, due to a higher short circuit current and fill factor. The 30 mm wide fingers reach specific contact resistances down to 0.6 mV cm 2 and also, pass a tape adhesion test. We further demonstrate that the laser process does not cause any measurable open circuit voltage loss and that a precise alignment of the two laser steps is not necessary.Silicon heterojunction (SHJ) solar cells are believed to play a major role in the future PV market [1] . Compared to homojunction solar cells, they offer a superior module performance due to their higher open circuit voltage and their lower temperature coefficient. Moreover, the production is relatively simple and does not require high temperature steps. However, a drawback for this technology still is the metallization. Screen printed metallization can only be applied with special expensive low temperature silver pastes [2] , because the passivation by the amorphous silicon (a-Si) layers of SHJ cells cannot withstand temperatures above 200-250 C [3] . Lowtemperature silver pastes reach resistivities between 5 and 10 mVcm [4] , which is far higher than for standard silver pastes sintered at high temperature (>800 C). The typical width of industrially produced screen printed fingers on SHJ cells lies between 60 and 80 mm.Cu-plating as a low temperature metallization is a more suitable technology. Kaneka has recently presented a plated SHJ solar cell with 25.1% efficiency, which represents the world record for both-sidecontacted SHJ solar cells [5] . Depending on the masking approach, plated fingers can be much thinner than screen printed fingers and the resistivity of plated metal is very close to that of bulk Cu (1.7 mVcm). In fact, plating has shown to outperform low temperature screen printing due to a higher fill factor (FF) [6] and a higher short circuit current (J SC ) [7] . High peel forces (3-5 N/mm) for plated copper fingers on TCO have been measured with an intermediate seed layer [8,9] . In addition, plating imposes less mechanical stress onto the wafer than screen printing, which is an advantage in view of thinner wafers expected in the future [1] .In order to plate a grid structure on the TCO surface of SHJ cells, in most cases, a structured organic plating mask is applied, which covers...

Native Oxide Barrier Layer for Selective Electroplated Metallization of Silicon Heterojunction Solar Cells

“…On the other hand, a plated metallization is intrinsically a low temperature process. Plated approaches using highly conductive and less expensive copper are currently investigated . The Cu‐based contacts can be electroplated simultaneously on both‐sides of the solar cells and TCOs like indium‐tin‐oxide (ITO) are good barrier to metals diffusion into silicon .…”

“…Plated approaches using highly conductive and less expensive copper are currently investigated. [12][13][14][15][16][17][18][19][20] The Cu-based contacts can be electroplated simultaneously on bothsides of the solar cells and TCOs like indium-tin-oxide (ITO) are good barrier to metals diffusion into silicon. [21] This manufacturing of plated bifacial SHJ solar cells intends to increase the contacts conductivity and reduces drastically the precious Ag consumption.…”

Dual‐Function Light‐Trapping: Selective Plating Mask of SiOx/SiNx Stacks for Silicon Heterojunction Solar Cells

“…Laser ablated Al 2 O 3 /a‐Si (amorphous silicon) stack was also employed as plating mask for SHJ solar cell . Rodofili et al has reported a pattern process combining NiV/Al 2 O 3 /TCO structure by laser induced forward transfer first and then NiV layer is laser fired through dielectric layer to form the contact …”

“…[23] Rodofili et al has reported a pattern process combining NiV/Al 2 O 3 /TCO structure by laser induced forward transfer first and then NiV layer is laser fired through dielectric layer to form the contact. [24] In this research, we proposed a low-cost approach to fabricate SiO x /SiN x stack as the top layer and M-ARCs for SHJ solar cell. With heat treatment, SiO x /SiN x stack act as in-situ deposited plating mask, combining with subsequent copper plating process, achieving better anti-reflective properties, and remarkably decreased resistivity loss with simplified process, which shows the potential to further improve photoelectric conversion efficiency.…”

A Universal Solution of Controlling the Distribution of Multimaterials during Macroscopic Manipulation via a Microtopography-Guided Substrate

“…Overall, many schemes have been proposed, among which the direct manipulating and positioning of the right atoms and molecules in the right place is the most attractive one. This can be divided into two categories: one is to manipulate the atom and molecule one by one (representing point-by-point manipulation), such as STM technology [12,13,14,15,16,17,18,19,20,21,22,23]; the other is to manipulate hundreds of millions of atoms and molecules (clusters) simultaneously (representing macroscopic manipulation), such as magnetron sputtering [24,25], molecular beam epitaxy [26,27], evaporation plating [28], sublimation [29], etc. Obviously, the former can manipulate atoms and molecules precisely to the designed places to manufacture objects [12,13,14,15,16,17,18,19,20,21,22,23]; however, this is practically difficult for large-sized objects [30].…”