Solar cells based on n+-AZO/p-BaSi2 heterojunction: Advanced opto-electrical modelling and experimental demonstration

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Abstract

We performed advanced opto-electrical simulations on thin-film BaSi2 solar cells. First, absorption spectra of BaSi2-pn homojunction solar cells on Si substrate were calculated based on flat and/or pyramidally-textured surfaces, wherein 20-nm-thick n+-BaSi2 was the topmost electron transport layer. By changing the front surface structure from flat to texture, the reflectance decreased in the wavelength (λ) range 700–1200 nm and the photocurrent density (Jph) delivered by the photogenerated carriers in the 500-nm thick p-BaSi2 layer increased by 1.2 mA/cm2. Simulations revealed that the key factor inhibiting light absorption in the p-BaSi2 layer was parasitic absorption in the n+-BaSi2 and in the c-Si substrate. To solve these optical issues, we propose a new device structure, Al-doped n+-ZnO (AZO, 50 nm)/i-ZnO (20 nm)/p-BaSi2 (500 nm) heterojunction solar cell (HJSC). In this device structure, the parasitic absorption reduced drastically, and Jph reached 30.23 mA/cm2. Furthermore, by replacing the Si substrate with a glass substrate, the light trapping worked more effectively, and the absorber layer thickness required for Jph to saturate was reduced to 1 μm, yielding 32.06 mA/cm2. Based on these simulation results, we manufactured n+-AZO/p-BaSi2 HJSC. The internal quantum efficiency exceeded 30% at λ = 600 nm, meaning that we demonstrated the operation of n+-AZO/p-BaSi2 HJSC for the first time. We investigated origins of small efficiencies compared to those simulated, and found that the passivation of defects in the p-BaSi2 layer and the reduction of carrier recombination at the i-ZnO/p-BaSi2 interface would significantly improve the solar cell performance.

Original languageEnglish
Article number111181
Number of pages12
JournalSolar Energy Materials and Solar Cells
Volume230
DOIs
Publication statusPublished - 2021

Keywords

  • Al-doped zinc oxide
  • Barium disilicide
  • Electron affinity
  • Parasitic absorption
  • Recombination

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