Low light performance is a critical metric in photovoltaic power generation, particularly in regions where solar irradiance fluctuates throughout the day. Standard module ratings are based on laboratory conditions of 1000 W per square metre, equivalent to clear midday sunlight. However, real world conditions rarely sustain this level, with lower irradiance dominating mornings, evenings, winter months and overcast periods.
Under such conditions, the ability of a module to maintain efficiency becomes essential for maximising energy yield. Ideally, module output should scale linearly with irradiance. In practice, internal electrical losses, particularly leakage current, reduce performance as light intensity drops.
Industry data shows that Tunnel Oxide Passivated Contact technology consistently outperforms Back Contact designs in weak light. At irradiance levels of 200 W per square metre, BC modules typically achieve 93% to 95% of expected output, while TOPCon modules such as JinkoSolar Tiger Neo 3.0 reach 96% to 97%.
The performance gap is primarily driven by differences in cell architecture. Leakage current, which reduces usable output, is closely linked to the quality of the p n junction and internal resistance. Higher shunt resistance limits leakage and preserves current flow.
Related news: JinkoSolar launches mass production of Tiger Neo 3 as global pre-orders exceed 15GW 
TOPCon cells benefit from a front and back electrode configuration that naturally separates p type and n type regions. This design improves junction integrity and significantly reduces leakage current. In contrast, BC cells place both regions on the rear side in an interdigitated layout, making effective isolation more difficult and increasing the likelihood of current loss. While this has minimal impact under strong sunlight, it becomes a major efficiency constraint under weak irradiance.
Spectral response further reinforces TOPCon’s advantage. Solar radiation under low light conditions contains a higher proportion of longer wavelength red light due to Rayleigh scattering in the atmosphere. The ability to capture and convert this portion of the spectrum is critical for maintaining output.
TOPCon cells demonstrate stronger responsiveness in the infrared and red spectrum. This is due to their reduced heavily doped rear surface area, which limits carrier recombination and parasitic absorption. In BC cells, the larger doped region on the back increases recombination losses, preventing effective utilisation of red light.
As a result, TOPCon modules are structurally better suited to convert available light into electricity during periods of low irradiance. The combination of reduced leakage current and improved spectral response enables more stable and higher energy yield across varying environmental conditions.
For energy developers and asset owners across Africa, where grid stability and generation consistency are key, these gains translate into improved project performance and stronger returns over the lifecycle of solar installations.
Author: Bryan Groenendaal

 






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