Efficiency - Page 3

Interface engineering plays a significant role in the constant improvement in the performance of perovskite photovoltaics, but such devices still suffer from several issues, including unavoidable open circuit voltage (VOC) losses. Now, an international team of researchers from Università Degli Studi Di Pavia, King Abdullah University of Science and Technology (KAUST), Chinese Academy of Sciences (CAS), University of Cambridge, Istituto Italiano di Tecnologia (IIT), Slovak Academy of Sciences and Imperial College London have proposed a different approach by creating a photo-ferroelectric perovskite interface. 

Graphical representation of the 2D/3D/2D perovskite heterostructure. Image from: Nature Communications

By engineering an ultrathin ferroelectric two-dimensional perovskite (2D) which sandwiches a perovskite bulk, the scientists exploited the electric field generated by external polarization in the 2D layer to enhance charge separation and minimize interfacial recombination. As a result, they observed a net gain in the device VOC reaching 1.21 V, the highest value reported to date for highly efficient perovskite PVs, leading to a champion efficiency of 24%. 

Two-dimensional Ruddlesden-Popper (2DRP) phase perovskites have excellent long-term environmental and structure stability. However, the efficiency of 2DRP perovskite solar cells (PSCs) still lags behind that of their 3D counterparts due to the large exciton binding energy between the large-volume organic spacer and the inorganic plate compared to their 3D analogs.

To address this issue, researchers from China's Northwestern Polytechnical University and Xijing University have used a thin layer of self-assembled monolayer material between the transporting layer and the perovskite film for efficient and stable 2DRP-based PSCs. 

Slot-die coating (SDC) technology is a potential approach to mass produce large-area, high-performance perovskite solar cells (PSCs) at low cost. However, when the interface in contact with the perovskite ink has low wettability, the SDC cannot form a uniform pinhole-free perovskite film, which reduces the performance of the PSC.

Optimizing Slot-Die Coating for Commercial Solar Cell Production. Image credit: InfinityPV

Researchers from Korea's Jeonbuk National University have examined the correlation between interfacial roughness, wettability, and the overall efficiency of perovskite solar cells produced using slot-die-coating. This work offers a comprehensive understanding of how modifying the roughness of the hole transport layer (HTL) can improve the quality of perovskite films, enhance charge transport, and ultimately lead to high-efficiency perovskite solar cells with long-term stability.

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 Chungnam National University and Russian Academy of Sciences have reported a method to increase the efficiency of perovskite solar cells (PSCs) by modifying the surface of a fluorine-doped indium tin oxide (FTO) substrate using an atmospheric pressure plasma treatment. 

The surface modification of the FTO film involved several challenges, such as control of the blocking layer uniformity, removal of pinholes, and deposition of a dense layer. This strategy allows the suppression of charge recombination at the interface between the FTO substrate and hole conductor. 

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.

Scientists at the Fraunhofer Institute for Solar Energy Systems ISE have developed a perovskite silicon tandem solar cell with 31.6% efficiency. 

The new 1 cm² solar cell is special in that the perovskite layer of the top cell was deposited on an industrially textured silicon heterojunction solar cell using a hybrid manufacturing route. The successful use of textured standard silicon solar cells and the uniform application of the perovskite layer on the texturized surface are important prerequisites for the industrial production of perovskite silicon tandem solar cells.

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.