Scientists from Shanghai Jiao Tong University and Wuhan University of Technology have fabricated a two-terminal (2T) tandem solar cell using a top semi-transparent perovskite layer and a bottom copper-indium-gallium-selenide (CIGS) cell.
They reported improved perovskite coverage on the rough, irregular surfaces of commercial CIGS substrates and reduced bulk defects – longstanding challenges for perovskite-CIGS tandem cells. The team said these surface features have historically hindered effective integration and limited performance.
Researchers used D-homoserine lactone hydrochloride (D-HLH) as an additive in the perovskite precursor to enhance crystallization of the absorber layer. This reportedly reduced film defects, enabled more uniform coverage, and improved the interface between the perovskite and CIGS layers.
The group also addressed interface recombination between the perovskite absorber and the buckminsterfullerene (C60) electron transport layer, where incomplete passivation traps minority carriers. They applied a dual passivation approach combining surface reconstruction and field-effect passivation.
“The surface reconstruction involves the use of 2-thiopheneethylammonium iodide (2-TEAI) and N,N-dimethylformamide (DMF), which effectively passivate the defect sites at the PVK surface and grain boundaries,” they explained. “Meanwhile, lithium fluoride (LiF) is introduced as a field-effect passivation layer, which repels hole carriers away from the perovskite/C60 interface, further reducing recombination losses.”
Following these two strategies, the researchers built the top perovskite device using a substrate of indium tin oxide (ITO), a nickel(II) oxide (NiOx) hole transport layer (HTL), a 2PACz-based self-assembled monolayer (SAM), a perovskite absorber, a C60 electron transport layer (ETL), a transparent indium zinc oxide (IZO) back contact, a LiF interlayer, and a silver (Ag) metal contact.
The device reached a power conversion efficiency of 19.1%, compared to 17.9% for a reference perovskite solar cell using the same architecture but without D-HLH or the dual passivation strategy. The researchers said they achieved an average efficiency above 21.8% with a combination of 2-TEAI and LiF, demonstrating the effectiveness of the dual passivation approach.
They then integrated the perovskite cell with a bottom CIGS cell in a 0.16 cm² tandem device that achieved 24.6% power conversion efficiency.
“Realizing both bulk and surface/interface passivation by the combined use of D-HLH, 2-TEAI, and LiF has mitigated PVK crystallization and complex interface carrier recombination issues,” it concluded.
The tandem cell was described in the study “Crystallization Modulation and Holistic Passivation Enables Efficient Two-Terminal Perovskite/CuIn(Ga)Se2 Tandem Solar Cells,” which was recently published in Nano-Micro Letters.
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