title: Interfacial Depletion Regions: Beyond the Space Charge Limit in Thick Bulk Heterojunctions.
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.
authors.affiliation: IMEC , Kapeldreef 75, Leuven B-3001, Belgium.|Department of Electrical Engineering, KULeuven , Kasteelpark Arenberg 10, Leuven B-3001, Belgium.
authors.forename: Jeffrey G
authors.initials: JG
authors.lastname: Tait
authors.affiliation: IMEC , Kapeldreef 75, Leuven B-3001, Belgium.
authors.forename: Ulrich W
authors.initials: UW
authors.lastname: Paetzold
authors.affiliation: IMEC , Kapeldreef 75, Leuven B-3001, Belgium.
authors.forename: David
authors.initials: D
authors.lastname: Cheyns
authors.affiliation: BASF Schweiz AG , CH-4002 Basel, Switzerland.
authors.forename: Mathieu
authors.initials: M
authors.lastname: Turbiez
authors.affiliation: IMEC , Kapeldreef 75, Leuven B-3001, Belgium.|Department of Electrical Engineering, KULeuven , Kasteelpark Arenberg 10, Leuven B-3001, Belgium.
authors.forename: Paul
authors.initials: P
authors.lastname: Heremans
authors.affiliation: Department of Electrical Engineering and Andlinger Center for Energy and the Environment, Princeton University , Princeton, New Jersey 08544, United States.
authors.forename: Barry P
authors.initials: BP
authors.lastname: Rand
keywords: bulk heterojunction; depletion region; optoelectrical model; space charge limited current; spray-coating