Researchers from Nanjing University in China have developed a perovskite-silicon tandem solar cell featuring an inverted perovskite top cell based on a new polymer hole-transport layer (HTL) that combines improved wettability with high film uniformity. The combination is intended to promote uniform perovskite deposition and create a homogeneous hole-selective interface, while enabling device fabrication under ambient conditions.
The scientists said that although inverted p–i–n perovskite solar cells offer advantages such as low-temperature processing, improved stability and compatibility with silicon bottom cells in tandem devices, scaling the technology from small cells fabricated in an inert atmosphere to large-area devices produced under ambient conditions remains challenging.
One of the key requirements for scalable production is an HTL that supports uniform coating and crystallization of the perovskite absorber. Such a layer requires good wettability and morphological uniformity, as well as efficient hole transport and strong adhesion to the transparent conductive oxide (TCO) substrate. Conventional poly(triarylamine) (PTAA) offers good charge transport and film uniformity, but its hydrophobic surface makes reproducible perovskite coating difficult. Carbazole phosphonic acid (PACz)-based self-assembled monolayers (SAMs), meanwhile, provide strong substrate binding but can suffer from poor film uniformity and a narrow processing window, particularly on textured silicon substrates.
To address these limitations, the research team developed PNCC, a copolymer combining triarylamine and PACz units. The material is designed to combine the charge-transport properties of PTAA-like polymers with the strong substrate-binding characteristics of PACz materials.
“In our work, we report a newly developed copolymer that enables high-performance perovskite solar cells,” corresponding author Shangshang Chen told pv magazine. “State-of-the-art p–i–n perovskite solar cells predominantly rely on two families of organic HTMs: SAMs and PTAA. Nevertheless, both materials suffer from intrinsic limitations: PTAA exhibits unsatisfactory wettability, while PACz-based SAMs lack sufficient film uniformity. Our newly designed PNCC copolymer addresses these inherent drawbacks simultaneously. Importantly, PNCC is compatible with both single-junction perovskite devices and perovskite-silicon tandem solar cells under ambient processing conditions.”
The researchers synthesized PNCC by copolymerizing PACz and triarylamine units at a molar ratio of 1:3, with the triarylamine units suppressing carbazole cyclization and improving charge transport. Further analysis showed that, compared with PTAA and Me-4PACz, PNCC provided a more uniform interface, with fewer voids at the buried PNCC/perovskite interface. Photoluminescence measurements also indicated reduced non-radiative recombination and longer carrier lifetimes. The researchers attributed these improvements to better film quality and defect passivation provided by PNCC’s phosphonic acid groups.
Based on this approach, the academics fabricated single-junction p–i–n perovskite solar cells via blade coating under ambient conditions.
The devices featured a planar architecture comprising a glass/indium tin oxide (ITO) substrate, the PNCC HTL, an approximately 800 nm perovskite absorber, a buckminsterfullerene (C60) electron-transport layer, a bathocuproine (BCP) buffer layer and a copper (Cu) contact. Both the PNCC and perovskite layers were blade-coated under ambient conditions.
Tested under standard illumination conditions, the champion device achieved a power conversion efficiency of 26.6%, an open-circuit voltage of 1.21 V, a short-circuit current density of 26.1 mA/cm² and a fill factor of 84.1%. An unidentified accredited third-party laboratory certified the device at 26.5% efficiency. By comparison, PTAA- and Me-4PACz-based reference cells achieved efficiencies of 23.5% and 24.1%, respectively.
In stability testing, the PNCC-based cell retained 99.8% of its initial efficiency after 1,200 hours of light soaking in air at around 40 C. It also retained 95.1% of its initial efficiency after 1,400 hours at 65 C and 92.8% after 1,200 hours at 85 C.
The researchers then applied PNCC as a standalone HTM in two-terminal perovskite-silicon tandem cells. The polymer formed conformal coatings on textured silicon without the aggregates observed with PTAA and Me-4PACz. The champion tandem device achieved a power conversion efficiency of 33.3%, with an independently certified efficiency of 33.0%. Across 18 tandem devices, the researchers reported an average efficiency of 32.0%.
The encapsulated tandem cell also retained 85% of its initial efficiency after 1,140 hours of one-sun illumination at 65 C in air.
The researchers said the results demonstrate the potential of ambient processing for producing stable, high-performance solar cells while providing a scalable pathway toward photovoltaic manufacturing.
The cell concept was presented in the study “Scalable ambient fabrication of single-junction and perovskite–silicon tandem solar cells,” published in Nature Sustainability.
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