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An international team of researchers has designed a two-terminal perovskite-silicon tandem solar cell that uses novel hybrid interconnect layers to reduce recombination losses in the top perovskite device. The tandem cell achieved an impressive fill factor of 81.8%, which the scientists say is the highest value recorded to date for this cell technology.
A group of researchers led by Chinas Jinan University has developed a two-terminal (2T) perovskite-silicon tandem solar cell based on special hybrid interconnect layers (ICLs) that avoid direct contact between the perovskite absorber and the transparent conducting oxide (TCO).
“Typical self-assembled monolayers (SAMs) directly on the transparent conductive oxide recombination (TCO) layer exhibit poor uniformity and compactness, resulting in high current losses and poor reproducibility of tandem solar cells,” Yousheng Wang, corresponding author of the research, told pv magazine . “To solve this problem, we proposed sputter-treated nickel oxide (NiOx) as the seed layer of SAMs to build the hybrid interconnect layers. The sputter-treatment technique provides easy coating on a complex substrate and high reproducibility.”
According to Wang, NiOx materials can further increase the coupling of SAM molecules with the substrate. Thus, hybrid ICLs could improve the interface uniformity between TCO and MeO-2PACz-based SAM, which is also known as [2-(3,6-Dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid, and reduce the leakage current. “Then, a good energy level alignment was constructed between perovskite and hybrid ICLs, which is beneficial for carrier extraction and transport,” he added. “Hybrid ICLs further decrease interface defects and bulk defects.”
The scientists constructed the tandem cell with a silicon heterojunction bottom device and an inverted perovskite top solar cell with 19.73% efficiency and 1.71 eV energy bandgap integrating the ICLs. The latter was designed with an indium tin oxide (ITO) substrate, a nickel(II) oxide (NiOx) hole transport layer (HTL), the MeO-2PACz SAM, a 2-phenylethylammonium iodide-doped (PEAI) perovskite absorber, a buckminsterfullerene (C60)-based electron transport layer (ETL), a transparent indium zinc oxide (IZO) back contact, and a silver (Ag) metal contact.
The performance of the tandem device was analyzed and compared with that of a reference cell based on a NiOx HTL but without the MeO-2PACz SAM. The latter achieved a power conversion efficiency of 22.27%, an open-circuit voltage of 1.75 V, a short-circuit current density of 17.85 mA cm-2 and a fill factor of 71.15%. The former obtained an efficiency of 28.47%, an open-circuit voltage of 1.88 V, a short-circuit current density of 18.25 mA cm-2 and a fill factor of 81.8%.
The group highlighted that the tandem cell fill factor is currently one of the highest in the scientific literature for perovskite-silicon devices. “NiOx/MeO-2PACz hybrid ICLs have been found to significantly reduce leakage current and non-radiative recombination losses by avoiding direct contact between perovskites and TCO,” they explain. “Our results provide an effective method to improve the uniformity and reduce the leakage current of the MeO-2PACz coating on the substrate.”
The solar cell was presented in the paper “ Hybrid interconnecting layers reduce current leakage losses in perovskite/silicon tandems with 81.8% fill factor ” published in Cell Reports Physical Science . The research group consisted of academics from Forschungszentrum Jülich GmbH in Germany, as well as Wuyi University and the University of Macau in China. |
