The Link between Ag‐Paste Rheology and Screen‐Printed Solar Cell Metallization

Abstract

printing machine technology with the goal of continuously increasing production throughput while improving alignment precision. Additionally, further paste development is conducted to enhance printed line geometry and contact formation. Over the last 15 years, screen printing of Ag-pastes for Si-solar cell metallization has become a success story by decreasing the printed electrode width from ≈120 µm in 2007 reported by Mette [2] toward only 20 µm reported by Tepner et al. in 2020. [3] Therefore, flatbed screen printing is catching up with other fine-line printing approaches for solar cell metallization. Recent studies reported finger widths down to 17 µm by using the parallel dispensing approach [4] and 20 µm by using pattern transfer printing. [5] Both results demonstrated homogenous line widths at competitive printing speeds. These achievements of screen printing have their origin in the continuous efforts of the industry around metallization to improve their technology and products and the scientific community providing an in-depth insight into the underlying physics around that topic. Over the years, the latter provided various research studies, focusing on understanding the impact of paste rheology, [6-10] optimizing the electrical performance of Ag-contacts, [11-14] and the impact of screen design on printing results. [6,15-19] Commonly available Ag-pastes for front-side PERC are highly filled suspensions containing up to 95 wt% spherical Ag-particles with diameters below 5 µm. [2,20] They show non-Newtonian flow characteristics with strong shear thinning behavior after exhibiting significant yield stress. [21,22] A fast and reproducible screen printing process imposes a few crucial requirements on the rheology because the paste is first excessively sheared when being transferred through a fine mesh. [23] Afterward, it is further pushed onto the substrate through the screen opening width w n and the height EOM (emulsion over mesh). During this motion, shearing should already be minimized because the recovery of the zero shear viscosity is highly time-dependent (thixotropic behavior). [6,24] Usually, this minimization of shearing within the screen opening is achieved by the paste's ability to slip at the emulsion surface. This effect has been the focus of several research studies, which showed how slip effects are enhancing screen-printing performance. [25-27] After the paste has been pushed through the screen opening onto the substrate, the Today's photovoltaic production chain is moving into a material crisis as the use of silver for front-side metallization of passivated emitter and rear contact solar cells remains a crucial requirement. The shared effort of the scientific and industrial community to further reduce Ag-consumption as much as possible without compromising cell efficiency has become more challenging in recent years. Further improvements require a deep understanding on the paste-screen interaction at narrow line widths. This study presents the impact of Ag-paste rheology on fine line screen ...

CIGS Mini‐Modules with Dispensed Metallization on Transparent Conductive Oxide Layer

“…The spreading coefficient ξ spreading describes the ratio of the finger width w core to the finger width w shading . [ 36,52 ] …”

“…The spreading coefficient ξ spreading describes the ratio of the finger width w core to the finger width w shading . [36,52] AR o ¼ h f ,max w shading (1) The CIGS mini-modules are prepared for the measurement as follows: after the P1 and P2 scribing, the metallization is applied on the TCO layer, and subsequently, the P3 structuring is realized mechanically. Hence, the P2 structures of the metallized CIGS mini-modules contain the TCO material and metal paste, whereas the P2 structures of the grid-free CIGS mini-modules include only the TCO layer.…”

Fluid‐Dynamics‐Processed Highly Stretchable, Conductive, and Printable Graphene Inks for Real‐Time Monitoring Sweat during Stretching Exercise

“…[23,24] Printing technologies are low-cost mass-production processes through which inks are transferred onto plastic, paper, textile, metallic, and ceramic substrates. [23][24][25][26][27][28] They are widely used to print a variety of wearable electronics, transistors, sensors, solar cells, batteries, supercapacitors, and other devices [23,24,[29][30][31][32][33][34][35] The formulation of functional inks with unique properties is essential for printing wearable sensors. [36][37][38] Recently, 2D layered graphene materials have attracted considerable attention as promising conductive fillers for printed flexible and stretchable devices owing to their high electrical conductivity, excellent mechanical properties, and good chemical stability.…”

Investigation of Thick-Film-Paste Rheology and Film Material for Pattern Transfer Printing (PTP) Technology

“…The paste viscosity, in contrast, seems not to correlate to the achieved aspect ratio, as can be seen in Figure 4d. It should be mentioned that the viscosity was shown to be a decisive parameter for a proper paste transfer through the screen mesh in screen-printing technology [17][18][19][20]. Our results indicate that the theoretical aspect ratio of 0.67 for trench 1 might be reached for a paste with higher yield stress or weaker dependence of yield stress on the temperature.…”