Interfacial Depletion Regions: Beyond the Space Charge Limit in Thick Bulk Heterojunctions

Jeffrey G. Tait, Ulrich W. Paetzold, David Cheyns, Mathieu Turbiez, Paul Heremans, Barry P. Rand

Research output: Contribution to journalArticle

21 Scopus citations

Abstract

Space charge limited photocurrent is typically described as the limiting factor in carrier extraction efficiency for organic bulk heterojunctions with increasing thickness. It successfully characterizes the carrier extraction efficiency in these devices with thin to moderate thickness and dissimilar carrier mobilities. However, in this article we show that space charge limited photocurrent cannot solely explain the intensity dependent spectral response of extremely thick organic photovoltaics. In addition, interfacial depletion regions near the contacts contribute to the field distribution and carrier collection. Here, we describe charge collection efficiency with an optical p-i-n model, allowing for collection from band bending due to mobility-induced and interfacial-doping-induced space charge regions. We verify the model with up to 1400 nm thick spray-coated devices in both p-i-n (conventional) and n-i-p (inverted) architecture, including variations of thickness, illumination intensity, transport materials, and bifacial (semitransparent) devices.

Original languageEnglish (US)
Pages (from-to)2211-2219
Number of pages9
JournalACS Applied Materials and Interfaces
Volume8
Issue number3
DOIs
StatePublished - Jan 27 2016

All Science Journal Classification (ASJC) codes

  • Materials Science(all)

Keywords

  • bulk heterojunction
  • depletion region
  • optoelectrical model
  • space charge limited current
  • spray-coating

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