The PERC+ cell: More output power for less aluminium paste

摘要

Passivated emitter and rear cell (PERC) technology has been forecast to become mainstream in the next few years, gaining around a 30% market share. This paper presents a novel PERC solar cell design in which a screen-printed rear aluminium (Al) finger grid is used instead of the conventional full-area Al rear layer, while implementing the same PERC manufacturing sequence. This novel cell concept, called 'PERC+', offers several advantages over PERC. In particular, the Al paste consumption for PERC+ cells is drastically reduced to 0.15g per wafer, as opposed to 1.6g per wafer for conventional PERC cells. The aluminium back-surface fields (Al-BSFs) created by the Al fingers are 2μm deeper, which increases the open-circuit voltage by 3mV. Moreover, the five-busbar Al finger grid enables the use of PERC+ cells in bifacial applications, offering front-side efficiencies of up to 21.2% and rear-side efficiencies of up to 16.6%, measured with a black chuck, and a corresponding bifaciality of up to 78%. When a reflective brass chuck is used for measurement, PERC+ cells demonstrate efficiencies of up to 21.5%, compared with 21.1% for conventional PERC cells. The PERC+ efficiency is higher, since the deeper aluminium back-surface field (Al-BSF) increases the open-circuit voltage and also because the reflective brass chuck increases the internal rear reflectance, leading to higher short-circuit currents. PERC+ cells are therefore expected to be an attractive candidate for both bifacial glass-glass modules and monofacial modules with a white backsheet. While ISFH developed the aforementioned PERC+, SolarWorld independently pioneered a very similar bifacial PERC+ cell process that has been successfully transferred to mass production. Novel glass-glass bifacial PERC+ modules based on a very simple, lean and cost-effective bifacial cell process were launched at Intersolar 2015. These new bifacial PERC+ modules have demonstrated an increase in annual energy yield between 5 and 25% in simulations, which has also been confirmed by the first outdoor measurements.