Photoinduced Bulk Polarization and Its Effects on Photovoltaic Actions in Perovskite Solar Cells

Ting Wu, Liam Collins, Jia Zhang, Pei Ying Lin, Mahshid Ahmadi, Stephen Jesse, Bin Hu

Research output: Contribution to journalArticle

20 Citations (Scopus)

Abstract

This article reports an experimental demonstration of photoinduced bulk polarization in hysteresis-free methylammonium (MA) lead-halide perovskite solar cells [ITO/PEDOT:PSS/perovskite/PCBM/PEI/Ag]. An anomalous capacitance-voltage (CV) signal is observed as a broad "shoulder" in the depletion region from -0.5 to +0.5 V under photoexcitation based on CV measurements where a dc bias is gradually scanned to continuously drift mobile ions in order to detect local polarization under a low alternating bias (50 mV, 5 kHz). Essentially, gradually scanning the dc bias and applying a low alternating bias can separately generate continuously drifting ions and a bulk CV signal from local polarization under photoexcitation. Particularly, when the device efficiency is improved from 12.41% to 18.19% upon chlorine incorporation, this anomalous CV signal can be enhanced by a factor of 3. This anomalous CV signal can be assigned as the signature of photoinduced bulk polarization by distinguishing from surface polarization associated with interfacial charge accumulation. Meanwhile, replacing easy-rotational MA+ with difficult-rotational formamidinium (FA+) cations largely minimizes such anomalous CV signal, suggesting that photoinduced bulk polarization relies on the orientational freedom of dipolar organic cations. Furthermore, a Kelvin probe force microscopy study shows that chlorine incorporation can suppress the density of charged defects and thus enhances photoinduced bulk polarization due to the reduced screening effect from charged defects. A bias-dependent photoluminescence study indicates that increasing bulk polarization can suppress carrier recombination by decreasing charge capture probability through the Coulombic screening effect. Clearly, our studies provide an insightful understanding of photoinduced bulk polarization and its effects on photovoltaic actions in perovskite solar cells.

Original languageEnglish
Pages (from-to)11542-11549
Number of pages8
JournalACS Nano
Volume11
Issue number11
DOIs
Publication statusPublished - 2017 Nov 28

All Science Journal Classification (ASJC) codes

  • Materials Science(all)
  • Engineering(all)
  • Physics and Astronomy(all)

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