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In this paper, we report on the stability of p-type passivated emitter and rear cells under ultraviolet (UV) exposure with various silicone nitride passivation coatings and embedded in different encapsulation polymers. Our results reveal that UV transparent polymers can result in a module power loss of up to 6% under a UV irradiation dose of 497 kWh/m 2 . We show that the degradation in power is caused by a reduction in open circuit voltage. This loss is related to an increased recombination in the cell, which we ascribe to a degradation of the surface passivation. With ray tracing simulations, we determine the number of photons reaching the passivation interface. Assuming that all photons with energies above 3.5 eV de-passivate the interface is in agreement with our experimental results.

We report on the UV radiation hardness of photovoltaic modules with bifacial n-type Passivated Emitter and Rear Totally diffused crystalline Si cells that are embedded in an encapsulation polymer with enhanced UV transparency. Modules with front junction cells featuring an AlO x /p þ -type Si passivation interface at the illuminated side are stable for a UV irradiation dose of 598 kWh m À2 . In contrast, irradiating modules with back junction cells featuring an a-SiN y /n þ -type Si passivation interface at the illuminated side reduces the output power by 15%. The quantum efficiency of the a-SiN ypassivated module degrades in the spectral range between 300 and 1000 nm, which we ascribe to a degradation of the surface passivation. Modeling the experimental data shows that photons with an energy above 3.4 eV contribute to the degradation effect and enhance the front surface recombination current density by a factor of 15.

This paper reviews the main research results related to PERC+ silicon solar cells. Compared to today's industry typical passivated emitter and rear cell (PERC) silicon solar cells with full-area rear aluminum layer, PERC+ solar cells apply an aluminum finger grid on the rear side and hence are able to absorb diffuse light from the rear side in addition to the direct sunlight which is absorbed from the front side. This bifaciality increases the energy yield of silicon solar modules by up to 25%. Since its first publication in 2015, the PERC+ cell concept has been rapidly adopted by several solar cell manufacturers due to the very similar process technology of bifacial PERC+ cells and main stream monofacial PERC cells. We summarize technological challenges, published PERC+ conversion efficiencies and PERC+ module technologies. First energy yield data of PERC+ field installations demonstrate the high energy yield potential of PERC+ solar cells.

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