Stability

Tokyo Chemical Industry (TCI), a global supplier of laboratory chemicals and specialty materials, is now offering Phenylethylamine Hydroiodides materials, used for surface treatment of perovskite layers in solar panels. These materials improve the stability of the solar panels.

Research has shown that by applying the Phenylethylamine Hydroiodides materials, one can expect improved stability of over 90%. In one research, the 1,2-Benzenediethanamine Dihydroiodide was applied to a perovskite PV device (FTO/TiO2/SnO2/perovskite/Amine Iodide/Spiro-OMeTAD/Au), and achieved an increase in stability of over 90% after 1,100 hours. See here for more info.

While formamidinium lead triiodide (FAPbI₃) perovskite can be used to create highly efficient perovskite solar cells (PSCs), the thermodynamically unstable α-phase poses a challenge to device long-term stability. Thermal annealing is essential for producing high-quality polycrystalline films that stabilize the α-FAPbI₃ phase, but it also induces partial decomposition of FAPbI₃ into PbI₂, leading to extra phase instability of FAPbI₃ films.

Researchers from the University of Science and Technology of China, Chinese Academy of Sciences, NingboTech University and Nankai University have developed a zero dimensional (0D) perovskite-decorated strategy to enhance the intrinsic stability of FAPbI₃ film by stabilization of the initially formed α-FAPbI₃ phase. 

Researchers from City University of Hong Kong, National Renewable Energy Laboratory (NREL) and Imperial College London have improved the long-term stability of perovskite solar cells with an atomic-layer deposition (ALD) method that replaces the fullerene electron transport layer with tin oxide. 

Professor Zhu Zonglong (left) and Dr Gao Danpeng of City University of Hong Kong hold their innovative solar cells. Image credit: Eurekalert

The team started by depositing the perovskite and the hole-transporter layer in a single step. Then, they used ALD to create an oxygen-deficient tin oxide layer to reduce the band offset to a thicker, overgrown layer of normal tin oxide. Solar cells had a power conversion efficiency of more than 25%, and they retained more than 95% of efficiency after 2000 hours of maximum power point operations at 65°C. 

Researchers from Thailand's Mahidol University, Rajamangala University of Technology Thanyaburi and Synchrotron Light Research Institute have presented two novel air-stable hole transporting materials (HTMs) based on a spiro[fluorene-9,9′-xanthene] (SFX) core functionalized with N-methylcarbazole (XC2-M) and N-hexylcarbazole (XC2-H) rings. 

These HTMs were synthesized via a straightforward, three-step process with good overall yields (∼40%) and low production costs. To further reduce device cost, carbon back electrodes were employed. The resulting PSCs, with a structure of FTO/SnO₂/Cs_0.05FA_0.73MA_0.22Pb(I_0.77Br_0.23)₃/HTM/C, achieved power conversion efficiencies (PCEs) of 13.5% (XC2-M) and 10.2% (XC2-H), comparable to the reference spiro-OMeTAD device (12.2%). 

Researchers from NingboTech University, Hunan Institute of Engineering, Hangna Nanofabrication Equipment Co. and University Malaysia Sabah have developed an inverted perovskite solar cell with an interface passivator based on lead carbanion (Pb–C^–), that reportedly achieved the highest open-circuit voltage ever recorded for an inverted perovskite PV device. The lead carbanion layer was responsible for reducing defects at the interface between the perovskite layer and the electron transport layer.

Inverted perovskite cells, or “p-i-n” cells, have the hole-selective contact p at the bottom of intrinsic perovskite layer i with electron transport layer n at the top. Conventional halide perovskite cells have the same structure but reversed – a “n-i-p” layout. In a n-i-p architecture, the solar cell is illuminated through the electron-transport layer (ETL) side; in the p-i-n structure, it is illuminated through the hole‐transport layer (HTL) surface. Inverted perovskite solar cells are known for their impressive stability but have been held back by relatively low efficiencies. This issue mainly arises at the point where the perovskite layer meets the electron transport layer, causing energy loss instead of being converted into useful power, primarily caused by carrier recombination, especially at the interface between perovskite and the electron transport layer.

Researchers from Korea's Daegu Gyeongbuk Institute of Science and Technology (DGIST), Gyeongsang National University (GNU) and Kookmin University have developed a method to improve both the performance and the stability of solar cells using perovskite quantum dots. They developed longer-lasting solar cells by addressing the issue of distortions on the surface of quantum dots, which deteriorate the performance of solar cells.

A schematic diagram of bilateral ligand bonding on the surface of perovskite quantum dots. Image credit: Chemical Engineering Journal

Perovskite quantum dots can have excellent light-to-electricity conversion capabilities and are easy to mass-produce. However, according to the research team, in order to utilize them in solar cells, the ligands attached to the quantum dot surface must be replaced. This process often leads to distortions of the quantum dot surface, resembling crumpled paper, which results in decreased performance and shorter lifespans for the solar cells. To address this issue, the team adopted short ligands that securely hold the quantum dots from both sides, effectively uncrumpling the distorted surface. The ligands help restore the distorted lattice structure, smoothing the crumpled surface of the quantum dots. This significantly reduces surface defects, enabling the solar cells to operate more efficiently and extending their lifespan. Consequently, the power conversion efficiency of the solar cells increased from 13.6% to 15.3%, demonstrating stability by maintaining 83% of their performance for 15 days.

In contrast to conventional (n–i–p) PSCs, inverted (p–i–n) PSCs offer enhanced stability and integrability with tandem solar cell architectures, which have garnered increasing interest. However, p–i–n cells tend to suffer from energy level misalignment with transport layers, imbalanced transport of photo-generated electrons and holes, and significant defects with the perovskite films.

Recently, researchers from King Abdullah University of Science and Technology (KAUST), Newcastle University, National Renewable Energy Laboratory (NREL) and Saudi Aramco Research and Development Center developed a nonionic n-type molecule (tris(2,4,6-trimethyl-3-(pyridin-3-yl)phenyl)borane (3TPYMB) that, through hydrogen bonding and Lewis acid–base reactions with perovskite surfaces or grain boundaries, enables in situ modulation of perovskite energetics, effectively mitigating the key challenges of p–i–n perovskite solar cells (PSCs). 

Researchers from CHOSE (Centre for Hybrid and Organic Solar Energy) at Tor Vergata University of Rome, CNR-ISM and Saule Technologies have introduced an optimized blade coating process for the scalable fabrication of large-area (15 cm × 15 cm) perovskite solar modules with a nickel oxide hole transport layer, performed in ambient air and utilizing a non-toxic solvent system. 

The research group fabricated a 110 cm² perovskite solar module with an inverted configuration and a hole transport layer that uses nickel oxide instead of commonly utilized poly(triarylamine) (PTAA). The proposed architecture aims to achieve high efficiency that is competitive with PTAA-based panels while improving stability.

Researchers from China's Northwestern Polytechnical University, The Hong Kong University of Science and Technology, and Spain's Technical University of Madrid have developed a new lithium-free doping strategy to fabricate spiro-OMeTAD-based hole transport layers (HTLs) for applications in perovskite solar cell. A PV device built with a lithium salt-doped HTL achieved an efficiency of 25.45%.

Schematic illustration of a n-i-p PSC with spiro-OMeTAD HTLs doped by LiTFSI or Eu(TFSI)₂. Image from Nature Communications

The team's lithium-free doping strategy to fabricate a perovskite solar cell is based on a metal-free hole transport layer (HTL) made of spiro-OMeTAd that reportedly offers remarkable efficiency and stability levels. The research team explained that spiro-OMeTAD for perovskite cell applications is usually doped with a compound known as lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to enhance hole extraction and conductivity. This kind of doping, however, requires time-intensive air-oxidization for 24 hours, which reportedly represents an obstacle to the commercial production of perovskite PV devices.

Researchers at the Nova University of Lisbon, University of Aveiro and University of York have created an ultra-thin perovskite solar cell with a checkerboard tile pattern that shields the perovskite layer from UV degradation. The design includes a luminescent down-shifting encapsulant, which enhances UV photon conversion and boosts overall efficiency.

The team provided background for this work, stating that advanced light management techniques can enhance the sunlight absorption of perovskite solar cells (PSCs). When located at the front, they may act as a UV barrier, which is paramount for protecting the perovskite layer against UV-enabled degradation. Although it was recently shown that photonic structures such as Escher-like patterns could approach the theoretical Lambertian-limit of light trapping, it remains challenging to also implement UV protection properties for these diffractive structures while maintaining broadband absorption gains.