Isolation of Hole Versus Electron Current at p-Si/TiO2 Selective Contact Using a Heterojunction Bipolar Transistor Structure

Janam Jhaveri, Alexander H. Berg, James C. Sturm

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

Carrier-selective contacts provide an exciting avenue for developing high-efficiency, low-cost silicon photovoltaics (PV). However, evaluating and understanding the different current mechanisms across a carrier-selective contact is difficult as the current measured represents the sum of both electron and hole current components. In this paper, we develop a heterojunction bipolar transistor (HBT) structure with the electron-selective p-type Si/titanium dioxide(TiO2)/Al contact as the base-emitter junction, which enables one to separately measure the electron and hole currents across the selective contact. An HBT with a current gain as large as ∼220 is achieved. The method is then used to evaluate the current mechanisms across a p-Si/TiO2/Al heterojunction PV cell, where the TiO2/p-Si replaces the n+-p junction. We determine that there is an optimal TiO2 thickness of 4.1 nm for CVD-deposited TiO2; and at the optimal thickness, the hole current is 8% of the total current, thus demonstrating that TiO2/Si is indeed a hole-blocking electron-selective contact. The hole current ratio is corroborated with reverse-recovery experiments, confirming the validity of the HBT method.

Original languageEnglish (US)
Pages (from-to)726-732
Number of pages7
JournalIEEE Journal of Photovoltaics
Volume8
Issue number3
DOIs
StatePublished - May 2018

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Electrical and Electronic Engineering

Keywords

  • Heterojunction
  • heterojunction bipolar transistor (HBT)
  • photovoltaics
  • selective contact
  • silicon
  • titanium dioxide

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