title: Origin of photogenerated carrier recombination at the metal-active layer interface in polymer solar cells.
abstract: The role of the metal-active layer interface in photogenerated recombination has been investigated using nanoscale current sensing atomic force microscopy (CS-AFM) and intensity modulated photocurrent spectroscopy (IMPS) in as-deposited, pre-annealed and post-annealed bulk heterojunction (BHJ) solar cells. Aluminum (Al) confined post-annealed BHJ solar cells exhibited a significantly improved device efficiency compared to pre-annealed BHJ solar cells having similar photocarrier harvesting ability in the active layer. The nanoscale topography and CS-AFM results indicate a uniform PCBM rich phase at the metal-active layer interface in the post-annealed cells, but PCBM segregation in the pre-annealed cells. These two different annealing processes showed different carrier dynamics revealed using IMPS under various light intensities. The IMPS results suggest reduced photo generated carrier recombination in uniform PCBM rich post-annealed BHJ solar cells. This study reveals the importance of the metal-bend interface in BHJ solar cells in order to obtain efficient charge carrier extraction for high efficiency.
authors.affiliation: Functional and Renewable Energy Materials Laboratory, Department of Physics, Indian Institute of Technology Ropar, Punjab 140 001, India. mkumar@iitrpr@ac.in.
authors.forename: Mukesh
authors.initials: M
authors.lastname: Kumar
authors.forename: Ashish
authors.initials: A
authors.lastname: Dubey
authors.forename: Khan Mamun
authors.initials: KM
authors.lastname: Reza
authors.forename: Nirmal
authors.initials: N
authors.lastname: Adhikari
authors.forename: Qiquan
authors.initials: Q
authors.lastname: Qiao
authors.forename: Venkat
authors.initials: V
authors.lastname: Bommisetty