A research group led by Jiangsu Ocean University in China has demonstrated a single-step surface texturing process that can reportedly boost absolute silicon solar cell efficiency of a tunnelling oxide passivating contact (TOPCon) by 1%. The cell-level performance was validated in laboratory and outdoor tests.
“This study introduces a novel, rapid single-step method for fabricating dense silicon submicron pyramids (SiSMPs) with an average base size of 0.68–0.76 μm by incorporating indium tin oxide additives into a conventional alkaline texturing solution,” first author of the research, Sihua Zhong, told pv magazine.
The researchers investigated SiSMPs surface texturing as a way to improve on the silicon micropyramids (SiMPs) currently used in industrial crystalline silicon solar cells. The study describes, in particular, an approach that “significantly simplifies” the SiSMPs fabrication process compared to existing multi-step or lithography-based techniques, according to Zhong. It also investigates the optimal functional films for use with SiSMPs to maximize solar cell optical gains.
“This novel single-step texturing process boosts solar cell efficiency by 1% absolute through broadband anti-reflection and lower electrical resistance,” Zhong said.
The study combined experimentation and simulation. In the experiments, the team used pseudo-square n-type Czochralski silicon (CZ Si) wafers, 110 μm thick and measuring 182 mm × 182 mm. Both TOPCon and silicon heterojunction (HJT) devices were fabricated with either SiSMPs or conventional SiMPs texturizing, and with either silicon nitride (SiNx) or indium tin oxide (ITO) films for comparison.
Outdoor electrical testing was carried out in a single day in April on a south-facing setup with a 34° tilt, matching the location’s latitude.
The results showed “enhanced energy yield for SiSMPs-textured devices” under both direct sunlight and shaded conditions. “The antireflection ability of the resulting submicron pyramid texture is much less sensitive to the incident angle than that of the micropyramid counterparts, leading to 6.8% higher daily energy output in outdoor tests,” Zhong said.
Shading performance improvements were also observed. “Interestingly, the modified devices show a 12% higher energy output than their conventional micropyramid-textured counterparts under shaded conditions,” Zhong added.
Optical performance of SiSMPs and SiMPs devices was modeled using finite-difference time-domain (FDTD) calculations, alongside other simulations. The team found that the engineered SiSMP structures exhibited “strong Mie scattering resonances” and lower reflectance than SiMP textures across a broad wavelength range.
Analysis attributed the improvements to reduced optical losses, which increased short-circuit current density by 0.7 mA/cm², and enhanced carrier collection through increased current pathways at the silver-silicon interface, boosting fill factor by 2.2% absolute.
Full-size SiSMP TOPCon devices achieved a power conversion efficiency (PCE) of 25.4%, representing a 1% absolute efficiency gain over SiMP-textured counterparts. HJT cells did not show the same broadband benefits in the EQE results, the researchers noted, attributing this to interference from doped amorphous silicon (a-Si:H) coating layers.
The researchers emphasized that these results are currently limited to the solar cell level, highlighting the need for further outdoor testing at the module level to confirm practical performance gains.
The study is detailed in “Surface texturing for advanced light management in crystalline silicon solar cells,” published in Renewable Energy. Other groups participating in the study were from JA Solar and Jiao Tong University.
Researching high-efficiency, low-cost crystalline silicon solar cell technologies is the group’s ongoing focus. “Our current projects include further optimizing the submicron surface texturing process by modifying the additives used and eliminating isopropanol, for instance; developing more reliable transparent conductive oxides with low indium content; and designing novel heterojunction solar cells that utilize wide-bandgap materials as carrier-selective contacts,” said Zhong.
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