The Role of Cutting-Edge Module Technology in Energy Transformation

Cut cells reduce the effective resistive losses in modules by lowering electric currents and it provides potentially higher shade tolerance. Due to these specific reasons, full cells have disappeared completely for wafer sizes larger than 182 mm × 182 mm. Half-cut cells are now the mainstream configuration and are expected to remain like this for the next decade. From a reliability perspective, the smaller cells resulting from cutting are less susceptible to cracking than larger cells. However, the cutting process introduces the potential for cell cracking due to defects along the cut edges. The risk of cell damage can be reduced by optimising the cutting process. Researchers have demonstrated that cutting cells via thermal laser separation produces less damage than cutting them via laser scribing and cleavage.

Starting from 2020, wafer thicknesses have dropped significantly to reduce polysilicon usage. Current predictions associate the thinnest wafer forecasts with n-type cell architectures, which best exploit the efficiency gains possible from thin wafers (~80µm especially in the cast of HJT). Thinner silicon cells are more flexible and thus come up with flexible modules with curved module designs. However, thinner cells inherently are more susceptible to cracking after they have been laminated inside a module. Thus a structured approach is required to address cell fracture risk, accounting for updated manufacturing processes, improved quality control, and overall PV module designs.

With respect to Interconnect technologies, three major changes are generally observed. These are increased redundancy, geometry, process changes, and material changes. In the past, a traditional three-busbar cell was utilized and subsequently moved to a five-busbar cell and 10-12 busbar configuration in the recent past. By including more busbars and interconnections, the individual ribbon size can be kept small, and the build-up of mechanical stresses can be reduced. More busbars and interconnections also enable reductions in cell finger width, which reduces costs by reducing silver metallisation and increases efficiency by increasing the active cell area. Very recently, the trend towards busbarless approach has significantly increased and in this case, the busbars are omitted, and the tabbing wires are directly connected to the grid fingers. Finally, shingled cells eliminate the gap between cells altogether, with cells overlapping each other by 1–2 mm and typically connected by electrically conductive adhesive (ECA). 

Structured foil and low-temperature solders lower the temperature requirements during the module packaging process and enable the use of new cell technologies, such as Heterojunction technology (HJT), which require lower processing temperatures after fabrication. Similarly, electrically conductive adhesives (ECA) can be cured at lamination temperature or below and is, therefore, suitable for temperature-sensitive technologies. It is already predictable that the round wires will displace the flat ribbons over the next decade, with increased use of structured foil and shingled technologies in the future.

Currently, there are contradictory results with respect to any difference in module operating temperature for glass–glass and glass–backsheet configurations. First, the increased temperature (reversibly) reduces power output by reducing cell efficiency. Second, the increased temperature can accelerate irreversible degradation processes, risking module reliability. Glass is a better thermal conductor compared to polymer backsheets and may dissipate heat more quickly, mitigating such concerns. However, recent work suggests that glass–glass module designs may introduce higher residual stresses into the cells during the lamination process compared with traditional glass–backsheet designs. As the encapsulant contracts, a typical polymer backsheet can contract with it, minimizing stresses. However, a rigid glass layer does not contract as easily with the encapsulant, resulting in higher cell deflections and stresses around the ribbon-shaped tapwires. This mechanism is especially prominent in laminates using EVA-based encapsulants, leading to higher cell stresses compared with laminates using POE-based encapsulants. Changing from EVA- to POE-based encapsulant reduces the effect of residual stresses in glass–glass type constructions because the storage modulus and Coefficient of thermal expansion (CTE) for POE are lower than for EVA

Making glass thinner than the standard 3.2mm is one solution to the challenges presented by heavy, large bifacial modules. Thinner glass reduces transportation and installation costs, and it enhances solar transmittance. ITRPV projections show front glass thicker than 3 mm losing market share primarily to glass between 2 and 3 mm thick (see Fig. 3a). Most of the rear glass (see Fig. 3b) is already thinner than front glass, at 2 to 3mm, and it is projected to continue thinning over time. Potential risks of thinner glass include reduced structural integrity and resistance to damage of modules from severe weather events and handling during installation. 

        Fig.3a ITRPV prediction for front glass    Fig. 3b ITRPV prediction for rear glass