title: Controlling the texture and crystallinity of evaporated lead phthalocyanine thin films for near-infrared sensitive solar cells.
abstract: To achieve organic solar cells with a broadened spectral absorption, we aim to promote the growth of the near-infrared (NIR)-active polymorph of lead phthalocyanine (PbPc) on a relevant electrode for solar cell applications. We studied the effect of different substrate modification layers on PbPc thin film structure as a function of thickness and deposition rate (rdep). We characterized crystallinity and orientation by grazing incidence X-ray diffraction (GIXD) and in situ X-ray reflectivity (XRR) and correlated these data to the performance of bilayer solar cells. When deposited onto a self-assembled monolayer (SAM) or a molybdenum oxide (MoO3) buffer layer, the crystallinity of the PbPc films improves with thickness. The transition from a partially crystalline layer close to the substrate to a more crystalline film with a higher content of the NIR-active phase is enhanced at low rdep, thereby leading to solar cells that exhibit a higher maximum in short circuit current density (JSC) for thinner donor layers. The insertion of a CuI layer induces the formation of strongly textured, crystalline PbPc layers with a vertically homogeneous structure. Solar cells based on these templated donor layers show a variation of JSC with thickness that is independent of rdep. Consequently, without decreasing rdep we could achieve JSC=10 mA/cm2, yielding a bilayer solar cell with a peak external quantum efficiency (EQE) of 35% at 900 nm, and an overall power conversion efficiency (PCE) of 2.9%.
authors.affiliation: imec , Kapeldreef 75, 3001 Heverlee, Belgium.
authors.forename: Karolien
authors.initials: K
authors.lastname: Vasseur
authors.forename: Katharina
authors.initials: K
authors.lastname: Broch
authors.forename: Alexander L
authors.initials: AL
authors.lastname: Ayzner
authors.forename: Barry P
authors.initials: BP
authors.lastname: Rand
authors.forename: David
authors.initials: D
authors.lastname: Cheyns
authors.forename: Christian
authors.initials: C
authors.lastname: Frank
authors.forename: Frank
authors.initials: F
authors.lastname: Schreiber
authors.forename: Michael F
authors.initials: MF
authors.lastname: Toney
authors.forename: Ludo
authors.initials: L
authors.lastname: Froyen
authors.forename: Paul
authors.initials: P
authors.lastname: Heremans
mesh_terms: D003460:Crystallization; D007259:Infrared Rays; D008982:Molybdenum / Q000737:chemistry; D009942:Organometallic Compounds / Q000737:chemistry*; D010087:Oxides / Q000737:chemistry; D012993:Solar Energy
chemical_list: C446702:Lead phthalocyanine; D009942:Organometallic Compounds; D010087:Oxides; C539565:molybdenum dioxide; D008982:Molybdenum