Perovskite/silicon tandem cells can overcome the efficiency limitations of single-junction cells, but ITO sputtering in semi-transparent top cells (ST-PSCs) causes plasma damage. Traditional ALD-SnO₂ buffer layers hinder industrialization due to slow deposition rates and high costs. This study proposes a solution-processed metal oxide nanoparticle buffer layer (PBL) alternative. It simultaneously leverages the intrinsic roughness of post-wafer-dicing silicon to simplify the process. By optimizing the AZO-N21X buffer layer and enhancing film uniformity through dynamic spin-coating, it achieves efficient light trapping on single-sided polished p-type silicon wafers (unpolished backside).

Millennial Perovskite Maximum Power Point Tracking Test MPPT serves as part of the standard testing protocol, enabling real-time optimization of load resistance to maintain the cell at its maximum power point (Pmax), thereby accurately recording steady-state power output. The final stacked efficiency achieved is 25.3% (two-step perovskite method), providing a low-cost pathway for industrialization.

Buffer Layer Material Screening

Cell Structures of Opaque Perovskite Solar Cells (PSCs) with Different Protective Buffer Layers (PBLs)

The research team developed a solution-processed buffer layer PBL based on metal oxide nanoparticles, prepared via spin-coating. They compared three nanoparticle dispersions: ZnO, AZO, and SnO₂.

(A) Statistical distribution of power conversion efficiency for perovskite cells with buffer layers treated by different solutions under static/dynamic coating; (B) Power conversion efficiency of semi-transparent perovskite cells using buffer layers treated by different solutions and sputtered ITO

Necessity of dynamic spin coating: Static coating prolongs solvent contact with the PCBM layer, leading to bubble-like voids that reduce the fill factor (FF). Dynamic coating minimizes interaction time and enhances film uniformity (e.g., FF of AZO N-21X increases from 73% static to 76% dynamic).

(A) UV absorption of buffer layer; (B) PL quenching ratio versus grain size; (C) XRD pattern

AZO N-21X demonstrated optimal performance:

Excellent UV shielding capability (UV absorption rate reaching 20%).

Preferential growth perpendicular to the (002) crystal plane, large grain size, and high charge transport efficiency.

Outstanding resistance to sputtering damage, with the lowest photoluminescence quenching ratio (PLQ) of 0.1.

Silicon-based cell structure optimization

Comparison of EQE for Polished/Unpolished Silicon Wafer Cells

Using a front-polished, back-unpolished P-type silicon heterojunction (SHJ) cell as the base cell, light trapping is achieved by leveraging the inherent roughness of the back surface after wafer cutting (σₘₛ=241 nm), eliminating the need for additional texturing steps. Experiments demonstrate that this structure enhances photocurrent by approximately 0.6 mA/cm² compared to double-polished wafers. Additionally, P-type silicon wafers are 8%-10% less expensive than N-type wafers, balancing performance and cost-effectiveness.

Translucent Top Cell Performance

ST-PSCs based on AZO N-21X buffer layers, fabricated via dynamic spin coating, achieved a PCE of 18.1%, approaching the 18.4% of opaque reference cells. They also demonstrated excellent open-circuit voltage (Voc) and fill factor (FF) performance, validating the effectiveness of solution-processed buffer layers.

Multilayer Cell Integration

Schematic Structure of Monolithic Perovskite/Silicon Tandem Solar Cells

Tandem Efficiency

(A) J-V curve of the all-solution-processed perovskite top cell; (B) J-V curve of the two-step hybrid perovskite top cell (with maximum power point tracking); (C) (D) EQE spectra of the two tandem cell types

The optimized top cell was integrated with a p-type silicon bottom cell to fabricate a single-junction tandem cell. MPPT continuously tracks steady-state maximum power, avoiding errors caused by forward/reverse bias in J-V scans and providing more reliable efficiency evaluation.

The all-solution perovskite top-cell tandem efficiency reached 23.2%.

Using a two-step mixing method (evaporating PbI₂ and CsBr followed by spin-coating FAI/MABr/MACl solutions), the perovskite top-cell tandem efficiency was further enhanced to 25.3%, with a fill factor (FF) approaching 77%.

Progress in fully planar silicon-based perovskite/silicon tandem cells across different studies, and the efficiency of back-unpolished/front-polished silicon-based tandem cells in this research (highlighting the performance improvement from back-unpolishing).

The tandem efficiency achieved using unpolished backside silicon wafers (25.3%) significantly surpasses literature reports for fully planar silicon-based cells (generally <23%), confirming the light management advantages of backside roughness.

This work developed a solution-processed AZO nanoparticle buffer layer that effectively protects perovskite/silicon tandem cells from transparent electrode sputtering damage. This buffer layer enabled a semi-transparent perovskite top cell efficiency of 18.1%. Combining pre-polished/post-unpolished p-type silicon substrate cells with the natural roughness of the silicon wafer back surface to enhance light capture eliminates the need for texturing processes. The final monolithic tandem cell efficiency reached 25.3%, offering a new pathway for low-cost, large-scale fabrication.

 Millennial Perovskite Maximum Power Point Tracking Test MPPT

email：market@millennialsolar.com

Perovskite Maximum Power Point Tracking Test MPPT employs A+AA+ grade LED solar simulators as aging light sources. With advanced technology and multifunctional design, it provides robust support for perovskite solar cell research.

▶ Light Source Grade: A+AA+, Spectral Matching Grade A+, Uniformity Grade A, Long-Term Stability Grade A+

▶ Effective Spot Size: ≥250*250mm (customizable)

▶ Adjustable Irradiance: 0.2-1.5 sun, adjustable in 0.1 sun increments

▶ Independently Controllable Power Bands: 300-400 nm / 400-750 nm / 750-1200 nm

Millennial Perovskite Maximum Power Point Tracking (MPPT) testing delivers steady-state efficiency of perovskite tandem cells under real-world operating conditions (rather than transient scan values), ensuring accurate and practical efficiency data.