The high-efficiency sustainable development of the photovoltaic industry requires simultaneous improvements in cell efficiency and aesthetics. Back-contact (BC) silicon solar cells, featuring a front-grid-free structure, combine high theoretical efficiency (29.2%) with aesthetic advantages. However, their low bifaciality rate (<80%) has constrained large-scale application.

This study proposes a dual-surface light management strategy: constructing hierarchical micrometer/submicrometer pyramids (HMS) on the light-receiving surface of tunnel-passivated back-contact (TBC) cells, while forming nano-polished surfaces (NPS) in the rear gap area. The Millennial QE quantum efficiency tester accurately quantifies the spectral response characteristics of different surface structures, such as HMS anti-reflective layers and NPS light traps. A commercial-scale 350 cm² single-junction silicon cell achieved a certified total area efficiency of 27.03%, with a bifacial ratio exceeding 80%, overcoming a critical barrier to BC technology industrialization.

Efficiency Records and Structural Innovations

TBC Solar Cell Structure and Performance; a: Schematic diagram of cell structure; b: I-V/P-V curves of 350 cm² cells; c: Comparison of different texturing processes; d: Efficiency distribution of mass-produced cells; e: Statistical values of Jₛc, Vₒc, and FF

I-V/P-V Curves of Record-Breaking Cells, Key Parameters:

Short-Circuit Current Density (Jsc): 42.32 mA/cm² (Significantly higher than literature values)

Open-Circuit Voltage (Voc): 744.7 mV

Fill Factor (FF): 85.77%

This efficiency breakthrough stems from the HMNS synergistic structure (HMS front surface + NPS rear gap zone):

Mass production statistics (130μm silicon wafers): HMNS average efficiency reaches 26.49%, a 0.24% improvement over conventional microtexture (CMS)

Current gain dominates: HMNS Jsc increases by 0.38 mA/cm², validating light management effectiveness

HMS front surface anti-reflection mechanism

HMS Surface Antireflection Mechanism; a-b: SEM images of CMS and HMS pyramids; c: Formation mechanism of HMS surface; d: Reflectance spectrum; e-f: Optical loss analysis of CMS and HMS cells;

Stepped submicron structures formed via mild alkaline etching:

Reflectance reduced to 13.47% (CMS: 17.24%), primarily due to increased critical angle (52°→60°) and enhanced submicron scattering

Optical loss analysis: Reflectance loss reduced by 0.42 mA/cm², EQE-integrated Jsc increased to 41.80 mA/cm²

Aesthetic optimization: HMS surface exhibits uniform dark color, resolving CMS multi-angle chromatic aberration

NPS back-gap light trap design

Surface Light Confinement Mechanism of NPS; a: Formation Mechanism of NPS; b: SEM Image of NPS Surface; c: Equivalent Principle of Gradient Refractive Index Layer; d-e: Optical Loss Comparison Between HMS and HMNS Cells

Nanosphere-Crown Structure (30-250 nm) Achieved via Selective Polishing with Calcium Salt Additives:

Gradient Refractive Index Effect: Equivalent Medium Theory Reduces Light Loss at Silicon-Air Interface

Light-limiting advantage: HMNS escape loss reduced to 2.65 mA/cm² (CMS: 2.71 mA/cm²)

Passivation synergy: NPS surface recombination current density (J₀) only 0.18 fA/cm², 1/4 that of CMS

Key technologies for passivation and recombination control

Passivation and recombination analysis; a: Effect of Al₂O₃ thickness on passivation efficiency; b: iVoc comparison; c: Carrier lifetime; d: Recombination mechanism decomposition; e-f: CMS vs. NPS surface area ratio and recombination rate

Al₂O₃/SiNₓ stack optimization: HMS passivation performance rivals CMS when ALD cycles exceed 43 (thickness >6 nm)

Recombination mechanism analysis: NPS surface recombination rate is only 1/3 that of CMS, attributed to smoother morphology and preferred crystal orientation

Carrier lifetime enhancement: NPS extends injection lifetime at maximum power point (MPP) by 15%

Bidirectional Efficiency and Power Synergistic Optimization

Dual-sided conversion rate and efficiency synergistic enhancement;a: Dual-sided conversion rate simulation prediction;b: Efficiency limit prediction;c: Battery efficiency statistics for different p/n junction widths;d: Electrical loss analysis

Breakthrough in dual-sided conversion rate achieved through p/n junction width reduction:

Experimental verification: At p/n=200μm, dual-sided conversion rate reaches 81.33% (simulation value 81.85%)

Efficiency gain: HMNS efficiency increased by 0.15% at p/n=200μm, significantly higher than CMS (0.05%)

Root cause: NPS reduces gap recombination losses; electrical analysis shows 40% reduction in surface recombination

Mass production prediction: HMNS cell theoretical efficiency reaches 27.06%

This study successfully developed a dual-sided micro-nano optical management strategy, achieving a world record total area efficiency of 27.03% (ISFH certified) on a 350 cm² commercial-scale tunneled oxide passivated back-contact (TBC) single-junction silicon solar cell, while simultaneously increasing the bifacial factor to 81.33%. This technology achieves an average reflectance of 13.47% and a short-circuit current density of 42.32 mA/cm² by constructing a stepped submicron pyramid structure (HMS) on the front surface. In the rear gap region, a nanosphere-crown polished surface (NPS) design utilizes the gradient refractive index effect to suppress light escape losses to 2.65 mA/cm². Combined with optimized Al₂O₃/SiNₓ passivation stacking (>6 nm), the composite current density in the NPS region is reduced to 0.18 fA/cm². This TOPCon-compatible manufacturing innovation provides a mass-producible solution for breaking through the 28% efficiency barrier of single-junction silicon cells.

Millennial QE Quantum Efficiency Tester

email：market@millennialsolar.com

The Millennial QE Quantum Efficiency Tester measures the spectral response of solar cells and diagnoses areas of low spectral response through quantum efficiency analysis. It offers universal compatibility, a broad spectral measurement range, testing accuracy, and traceability.

Compatible with all solar cell types to meet diverse testing requirements

Spectral range extends from 300-2500nm with specialized customization options

Dual light source structure (xenon lamp + halogen lamp) ensures stable illumination

By measuring key parameters such as EQE (external quantum efficiency), IQE (internal quantum efficiency), reflectance, and short-circuit current density, the Millennial QE Quantum Efficiency Tester precisely analyzes the spectral response characteristics of TBC cells. This provides data support for optimizing backside passivated contacts (e.g., TOPCon layer) and light management strategies.