Tandem

The fabrication of perovskite/Si tandem solar cells often encounters the challenge of selecting a suitable sputtering buffer layer (SBL) to prevent damage during the transparent electrode deposition. In their recent work, researchers from China's Northwestern Polytechnical University and Shaanxi Joint Laboratory of Graphene (NPU), Chinese Academy of Sciences and Ningbo New Materials Testing and Evaluation Center Co. developed a perovskite-silicon tandem solar cell that uses an indium oxide sputtering buffer layer to protect the perovskite absorber and the electron transport layer from damages that might occur during the electrode deposition process. The new layer not only granted this protection but also showed strong optical and electrical properties. 

The team introduced the indium oxide (In₂O₃) buffer layer via e-beam deposition to fabricate semi-transparent perovskite solar cells. The optical transmittance and electrical conductivity of In₂O₃ highly depend on the deposition rate. High deposition rate results in high ratio of metallic indium in the film, which causes severe parasitic absorption. A 20 nm-thick In₂O₃ film deposited at lower rate demonstrated high conductivity, transmittance and robust protection during sputtering. 

Researchers from Zhejiang University, Soochow University, King Abdullah University of Science and Technology (KAUST), The Hong Kong Polytechnic University and Suzhou Maxwell Technologies have addressed common challenges related to hole transport layers that are commonly used for the perovskite top cells, such as defects, non-conformal deposition or de-wetting of the overlying perovskite on the textured silicon bottom cells.

The team decided to develop a strategy based on co-deposition of copper(I) thiocyanate and perovskite, where effective perovskite grain boundary passivation and efficient hole collection are simultaneously achieved by the embedded copper(I) thiocyanate, which creates local hole-collecting contacts. Fabricated monolithic perovskite/silicon tandem devices achieved a certified power conversion efficiency of 31.46% for 1 cm² area devices. 

The certified efficiency of 1 cm² scale all-perovskite tandem solar cells tends to lag behind that of their small-area (~0.1 cm2) counterparts. This performance deficit originates from inhomogeneity in wide-bandgap (WBG) perovskite solar cells (PSCs) at a large scale. The inhomogeneity is thought to be introduced at the bottom interface and within the perovskite bulk itself. 

Researchers from Nanjing University, Jilin University, University of Cambridge, University of Victoria, The Australian National University, Chinese Academy of Sciences (CAS) and Renshine Solar (Suzhou) have reported an all-perovskite tandem solar cell based on a wide-bandgap top perovskite cell with a 20.5% efficiency. 

Researchers from the  Chinese Academy of Sciences (CAS) and Zhejiang University have developed a highly passivated TOPCon bottom cell, achieving perovskite/silicon tandem solar cells (TSCs) with high open-circuit voltages (VOCs) and excellent efficiencies. 

The structure and performance of tandem devices with highly passivated TOPCon bottom cells. Image by Ningbo Institute of Materials Technology and Engineering (NIMTE) 

Numerous defects at the fragile silicon oxide/c-Si interface and the weak field-effect passivation on textured substrates reduce the VOCs of current TOPCon silicon solar cells, thus limiting their application for high-performance perovskite/silicon TSCs. In this study, the researchers prepared highly passivated p-type TOPCon structures and double-sided TOPCon bottom cells on industrial textured wafers via industry-compatible fabrication methods, including ambient-pressure thermal oxidation and in situ plasma-enhanced chemical vapor deposition.

Researchers from Helmholtz Zentrum Berlin (HZB) and École Polytechnique Fédérale de Lausanne (EPFL) have presented optimization strategies for top cell processing and integration into silicon heterojunction (SHJ) bottom cells based on industrial Czochralski (Cz)-Si wafers of 140 μm thickness. 

Schematic illustration of the perovskite/silicon tandem solar cell based on 140 μm Cz-Si. Image credit: ACS Applied Materials & Interfaces

The team showed that combining the self-assembled monolayer [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz) with an additional phosphonic acid (PA) with different functional groups, can improve film formation when used as a hole transport layer improving wettability, minimizing shunt fraction and reducing nonradiative losses at the buried interface. 

Semi-transparent solar cells are appealing for many different applications such as building-integrated photovoltaics (BIPVs), tandem solar cells and in wearable electronics. Perovskites could be ideal for semi-transparent applications as they are versatile and easy to optimize.

Semi-transparent perovskite solar cells (ST-PSCs) must try to maximize efficiency and transparency. Methods such as bandgap engineering, thinning perovskite layers, and creating discontinuous structures are being developed to improve their performance. However, challenges still remain with ST-PSC development, such as phase stability and defect management.

Researchers from King Abdullah University of Science and Technology (KAUST) and  Helmholtz-Zentrum Berlin (HZB) have developed a perovskite-silicon tandem solar cell that achieves efficient charge extraction and interface passivation. The team improved the performance of blade-coated tandems by introducing 2D perovskite layers at the bottom interface. 

Image credit: Joule

These modifications enhanced the blade-coated tandem performance to a certified PCE of 31.2%, owing to efficient charge extraction and interface passivation. This work demonstrates the efficiency potential for scalable ink-based fabrication, emphasizing stability and manufacturability, which are crucial for the widespread adoption and commercial success of this promising photovoltaic (PV) technology.

Together with his collaborators at Helmholtz-Zentrum Berlin and Technical University of Berlin, Dr. Felix Lang from the University of Potsdam previously launched perovskite tandem solar cells into space to test their performance with extreme radiation levels and temperature cycles. Recently, he successfully received the first data from his experiment.

July 9, 2024 was the day of the maiden launch of the new Ariane 6 rocket from Guiana Space Centre by ESA. On-board a satellite was a special solar cell experiment. The satellite itself was successfully released one hour and six minutes after launch. “The solar cells have survived launch and started to produce energy, even without perfect alignment to the sun,” says Felix Lang, who celebrates this first success with his junior research group at the chair of Prof. Dr. Dieter Neher, funded by a Freigeist-Fellowship of the Volkswagen Foundation.

Jiangsu Xiehang Energy Technology (Fellow Energy/Xiehang Energy), a holding company of Turkey’s Chen Solar photovoltaic module and smart device manufacturer, has announced its plan to build a perovskite solar cell and module factory in Sichuan Province, China.

Fellow Energy had negotiated with the local government of Dechang County, Sichuan Province, for the construction of the project. It plans to build a solar cell factory to produce 2GW of perovskite-silicon tandem solar cells and 5GW of high-efficiency solar modules annually upon completion of the facility.

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).