为了实现净零排放，提高太阳能电池效率至关重要。多结太阳能电池，特别是三结太阳能电池，因其能最大化太阳能转化效率而备受关注。尽管理论上效率可达51%，但材料限制常使其表现不如预期。近期，一个国际研究团队在《Nature Nanotechnology》上发表文章，展示了迄今为止最大且最高效的三结钙钛矿-硅串联太阳能电池。该团队通过优化钙钛矿材料化学和器件设计，成功解决了表面缺陷问题，并采用了新的材料组合，如用PDCl取代氟化锂，用铷取代甲胺，以及使用金纳米颗粒连接钙钛矿结。最终，他们开发出了16平方厘米的器件，实现了23.3%的稳定态功率转换效率，创下了大面积器件的记录，并在严格的热循环测试中表现出色，预示着其在实际应用中的巨大潜力。

☀️ **大面积高效太阳能电池的开发是实现净零排放的关键。** 多结太阳能电池，尤其是三结太阳能电池，通过堆叠具有不同带隙的半导体材料，能够更有效地捕获太阳光谱的各个部分，从而最大化太阳能到电力的转换效率。尽管理论上三结太阳能电池的功率转换效率（PCE）可达51%，但实际制备中面临材料选择、成本和制造复杂性等挑战，导致性能远未达到理论极限。

🌟 **钙钛矿材料在太阳能电池领域展现出巨大潜力。** 钙钛矿材料因其成本效益高、效率可观、易于制造以及能与硅结合形成多结器件等优点，成为当前太阳能电池研究的热点。研究人员通过直接在硅基底上逐层制造钙钛矿层，实现了单片集成，减少了连接点数量。然而，钙钛矿层中的表面缺陷仍然是影响其性能和稳定性的一个关键因素。

🔬 **创新材料和设计显著提升了三结钙钛矿-硅太阳能电池的性能与稳定性。** 为解决表面缺陷问题，研究团队采用了一种名为哌嗪-1,4-二鎓氯化物（PDCl）的材料替代传统的氟化锂，并用铷（rubidium）替代了常用的甲胺（methylammonium）。这些改变不仅提高了器件的耐光稳定性，还通过优化金纳米颗粒在氧化锡上的连接方式，促进了电荷的有效传输和光的吸收。这种精细的工程优化，特别是在最小化颗粒覆盖率同时保证足够欧姆接触以实现垂直载流子流动方面，为提高器件性能提供了宝贵的经验。

🚀 **创纪录的大面积三结钙钛矿太阳能电池的诞生。** 研究团队成功开发出面积为16平方厘米的三结钙钛矿-硅串联太阳能电池，并获得了独立认证的23.3%的稳态功率转换效率，这是目前报道的最大面积器件的最高纪录。尽管在1平方厘米的测试器件上，全钙钛矿三结电池效率可达28.7%，钙钛矿-硅三结电池效率可达27.1%，但本次研究的重点在于大面积器件的突破。此外，该1平方厘米器件还通过了国际电工委员会（IEC）61215热循环测试，证明了其在极端温度变化下的可靠性，在407小时连续运行后仍保持了95%的初始效率。

💡 **该技术预示着太阳能电池在实际应用中的广阔前景。** 此次研究成功实现了大面积器件的高效率和良好的稳定性，结合其通过严格的热循环测试，表明这种三结太阳能电池架构在不久的将来可能在实际应用中发挥重要作用，尽管距离理论极限仍有提升空间。

Improving the efficiency of solar cells will likely be one of the key approaches to achieving net zero emissions in many parts of the world. Many types of solar cells will be required, with some of the better performances and efficiencies expected to come from multi-junction solar cells. Multi-junction solar cells comprise a vertical stack of semiconductor materials with distinct bandgaps, with each layer converting a different part of the solar spectrum to maximize conversion of the Sun’s energy to electricity.

When there are no constraints on the choice of materials, triple-junction solar cells can outperform double-junction and single-junction solar cells, with a power conversion efficiency (PCE) of up to 51% theoretically possible. But material constraints – due to fabrication complexity, cost or other technical challenges – mean that many such devices still perform far from the theoretical limits.

Perovskites are one of the most promising materials in the solar cell world today, but fabricating practical triple-junction solar cells beyond 1 cm² in area has remained a challenge. A research team from Australia, China, Germany and Slovenia set out to change this, recently publishing a paper in Nature Nanotechnology describing the largest and most efficient triple-junction perovskite–perovskite–silicon tandem solar cell to date.

When asked why this device architecture was chosen, Anita Ho-Baillie, one of the lead authors from The University of Sydney, states: “I am interested in triple-junction cells because of the larger headroom for efficiency gains”.

Addressing surface defects in perovskite solar cells

Solar cells formed from metal halide perovskites have potential to be commercially viable, due to their cost-effectiveness, efficiency, ease of fabrication and their ability to be paired with silicon in multi-junction devices. The ease of fabrication means that the junctions can be directly fabricated on top of each other through monolithic integration – which leads to only two terminal connections, instead of four or six. However, these junctions can still contain surface defects.

To enhance the performance and resilience of their triple-junction cell (top and middle perovskite junctions on a bottom silicon cell), the researchers optimized the chemistry of the perovskite material and the cell design. They addressed surface defects in the top perovskite junction by replacing traditional lithium fluoride materials with piperazine-1,4-diium chloride (PDCl). They also replaced methylammonium – which is commonly used in perovskite cells – with rubidium. “The rubidium incorporation in the bulk and the PDCl surface treatment improved the light stability of the cell,” explains Ho-Baillie.

To connect the two perovskite junctions, the team used gold nanoparticles on tin oxide. Because the gold was in a nanoparticle form, the junctions could be engineered to maximize the flow of electric charge and light absorption by the solar cell.

“Another interesting aspect of the study is the visualization of the gold nanoparticles [using transmission electron microscopy] and the critical point when they become a semi-continuous film, which is detrimental to the multi-junction cell performance due to its parasitic absorption,” says Ho-Baillie. “The optimization for achieving minimal particle coverage while achieving sufficient ohmic contact for vertical carrier flow are useful insights”.

Record performance for a large-scale perovskite triple-junction cell

Using these design strategies, Ho-Baillie and colleagues developed a 16 cm² triple-junction cell that achieved an independently certified steady-state PCE of 23.3% – the highest reported for a large-area device. While triple-junction perovskite solar cells have exhibited higher PCEs – with all-perovskite triple-junction cells reaching 28.7% and perovskite–perovskite–silicon devices reaching 27.1% – these were all achieved on a 1 cm² cell, not a large-area cell.

In this study, the researchers also developed a 1 cm² cell that was close to the best, with a PCE of 27.06%, but it is the large-area cell that’s the record breaker. The 1 cm² cell also passed the International Electrotechnical Commission’s (IEC) 61215 thermal cycling test, which exposes the cell to 200 cycles under extreme temperature swings, ranging from –40 to 85°C. During this test, the 1 cm² cell retained 95% of its initial efficiency after 407 h of continuous operation.

The combination of the successful thermal cycling test combined with the high efficiencies on a larger cell shows that there could be potential for this triple-junction architecture in real-world settings in the near future, even though they are still far away from their theoretical limits.

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