High-Efficiency Perovskite-Silicon Tandem Solar Cells with Self-Assembled Monolayer Interlayers Achieving 31.2% Power Conversion Efficiency
Abstract
We report monolithic perovskite-silicon tandem solar cells with a certified power conversion efficiency of 31.2%, surpassing the single-junction Shockley-Queisser limit. The key innovation is a self-assembled monolayer (SAM) of [2-(9H-carbazol-9-yl)ethyl]phosphonic acid (2PACz) deposited on an indium tin oxide (ITO) recombination layer, which provides optimal energy level alignment and minimizes interfacial recombination losses. The tandem device employs a 1.68 eV wide-bandgap Cs₀.₀₅FA₀.₈MA₀.₁₅PbI₂.₅Br₀.₅ perovskite top cell and a silicon heterojunction (SHJ) bottom cell. Outdoor stability testing over 1,000 hours under maximum power point tracking shows only 8.5% relative efficiency degradation.
Keywords: perovskite solar cells, tandem solar cells, silicon heterojunction, self-assembled monolayer, photovoltaics
1. Introduction
Single-junction crystalline silicon solar cells dominate the photovoltaic market with >95% market share, but their efficiency is approaching the theoretical Shockley-Queisser limit of ~29.4%. Perovskite-silicon tandem architectures offer a pathway to surpass this limit by harvesting a broader spectrum of solar radiation — the wide-bandgap perovskite top cell absorbs high-energy photons while transmitted low-energy photons are captured by the silicon bottom cell.
2. Device Fabrication
The monolithic tandem device stack consists of: Ag grid / MgF₂ / ITO / C₆₀ / perovskite / 2PACz SAM / ITO recombination layer / a-Si:H(n) / c-Si(n) / a-Si:H(i) / a-Si:H(p) / ITO / Ag. The perovskite layer was deposited by a two-step sequential deposition method in a nitrogen-filled glovebox.
Table 1. Photovoltaic parameters of champion tandem cells with different interlayer treatments
| Interlayer | VOC (V) | JSC (mA/cm²) | FF (%) | PCE (%) |
|---|---|---|---|---|
| None (bare ITO) | 1.82 | 19.1 | 76.2 | 26.5 |
| PTAA | 1.88 | 19.4 | 79.5 | 29.0 |
| NiOx | 1.86 | 19.5 | 78.1 | 28.3 |
| 2PACz SAM | 1.92 | 19.8 | 82.1 | 31.2 |
3. Results and Discussion
The J-V characteristics of the champion tandem device are shown in Figure 1. The 2PACz SAM interlayer yields a remarkable open-circuit voltage of 1.92 V, which is within 95% of the radiative limit, indicating minimal non-radiative recombination at the perovskite/transport layer interfaces.
4. Conclusions
We have demonstrated that self-assembled monolayer interlayers are a transformative approach for perovskite-silicon tandem solar cells, achieving a certified 31.2% power conversion efficiency. The 2PACz SAM provides simultaneously improved V_OC, J_SC, and fill factor through superior energy level alignment, passivation of interfacial defects, and enhanced charge extraction. Combined with the demonstrated 1,000-hour operational stability, these results move perovskite-silicon tandems closer to commercial viability for next-generation photovoltaics.
References
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