Researchers from the Indian Institute of Technology Roorkee, CSIR-National Physical Laboratory and Academy of Scientific and Innovative Research (AcSIR) have designed a solution-based fabrication approach involving a high-performance semi-transparent perovskite cell (ST-PSC) stacked in tandem with a hybrid heterojunction silicon solar cell (HHSC).
The hybrid heterojunction solar cell was embedded as a bottom device in a four-terminal perovskite-silicon solar cell using the new solution processing technique. The novel cell architecture, according to the team, could be produced at significantly lower costs compared to conventional perovskite-silicon tandem designs.
The researchers proposed to use hybrid heterojunction solar cells (HHSCs) as bottom devices in four-terminal (4T) perovskite-silicon tandem PV cells as HHSCs have a simple structure and can be produced using low-temperature fabrication processes, while also showing promising efficiencies. “These HHSCs aim to eliminate up to 35% of energy consumption during solar cell production and exploit the advantages of both functional layer and Si materials in a cost-effective approach,” the team stated in their work, noting that these cells are based on carrier-selective functional layers relying on either molybdenum oxide (MoOx), graphene, carbon nanotube (CNT), PEDOT:PSS, or poly(3-hexylthiophene) (P3HT).
For their new HHSC architecture, the research team chose PEDOT:PSS, which is a polymer known for its low cost and easy preparation properties. It was fabricated with a silver (Ag) metal contact, a textured n-type silicon (n-Si) absorber coated with PEDOT:PSS, and an indium gallium (In:Ga) interface. Its power conversion efficiency reached 10.92% and the fill factor was 66.04%.
The textured surface of the n-Si absorber is claimed to reduce surface reflectance while providing saw-damage free/smooth surface and increased junction area, which is crucial for high quality and efficient PEDOT:PSS/n-Si junction formation. “The addition of ethylene glycol in the PEDOT:PSS enhances its electrical conductivity and induces a strong inversion layer at PEDOT:PSS/n-Si interface near the n-Si surface,” the group said, noting that the cell was prepared using a solution processing technique.
The top perovskite device was constructed with a transparent fluorine-doped tin oxide (FTO) substrate, a hole transport layer (HTL) made of nickel(II) oxide (NiOx), a perovskite absorber, an electron transport layer (ETL) based on phenyl-C61-butyric acid methyl ester (PCBM) and molybdenum trioxide (MoO3), an Rh101 buffer layer and a silver (Ag) metal contact.
This collaborative integration of efficient ST-PSC along with a cost-effective HHSC yielded a 4-terminal tandem efficiency of 15.41%, a substantial enhancement of over 41% compared to the standalone HHSC under standard 1 sun illumination conditions. The concept was further confirmed by the results of SCAPS-1D simulation. These findings open the door to developing next generation solution processable 4T tandem solar cells.
