Analysis of wet chemical tunnel oxide layer characteristics capped with phosphorous doped amorphous silicon for high efficiency crystalline Si solar cell application

  • Kang, Ji-yoon (College of Information and Communication Engineering, Sungkyunkwon University) ;
  • Jeon, Minhan (College of Information and Communication Engineering, Sungkyunkwon University) ;
  • Oh, Donghyun (College of Information and Communication Engineering, Sungkyunkwon University) ;
  • Shim, Gyeongbae (College of Information and Communication Engineering, Sungkyunkwon University) ;
  • Park, Cheolmin (Department of Energy Science, Sungkyunkwon University) ;
  • Ahn, Shihyun (College of Information and Communication Engineering, Sungkyunkwon University) ;
  • Balaji, Nagarajan (Department of Energy Science, Sungkyunkwon University) ;
  • Yi, Junsin (College of Information and Communication Engineering, Sungkyunkwon University)
  • Published : 2016.02.17

Abstract

To get high efficiency n-type crystalline silicon solar cells, passivation is one of the key factor. Tunnel oxide (SiO2) reduce surface recombination as a passivation layer and it does not constrict the majority carrier flow. In this work, the passivation quality enhanced by different chemical solution such as HNO3, H2SO4:H2O2 and DI-water to make thin tunnel oxide layer on n-type crystalline silicon wafer and changes of characteristics by subsequent annealing process and firing process after phosphorus doped amorphous silicon (a-Si:H) deposition. The tunneling of carrier through oxide layer is checked through I-V measurement when the voltage is from -1 V to 1 V and interface state density also be calculated about $1{\times}1012cm-2eV-1$ using MIS (Metal-Insulator-Semiconductor) structure . Tunnel oxide produced by 68 wt% HNO3 for 5 min on $100^{\circ}C$, H2SO4:H2O2 for 5 min on $100^{\circ}C$ and DI-water for 60 min on $95^{\circ}C$. The oxide layer is measured thickness about 1.4~2.2 nm by spectral ellipsometry (SE) and properties as passivation layer by QSSPC (Quasi-Steady-state Photo Conductance). Tunnel oxide layer is capped with phosphorus doped amorphous silicon on both sides and additional annealing process improve lifetime from $3.25{\mu}s$ to $397{\mu}s$ and implied Voc from 544 mV to 690 mV after P-doped a-Si deposition, respectively. It will be expected that amorphous silicon is changed to poly silicon phase. Furthermore, lifetime and implied Voc were recovered by forming gas annealing (FGA) after firing process from $192{\mu}s$ to $786{\mu}s$. It is shown that the tunnel oxide layer is thermally stable.

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