title: Barium: an efficient cathode layer for bulk-heterojunction solar cells.
abstract: We report Barium (Ba) cathode layer for bulk-heterojunction solar cells which enhanced the fill factor (FF) of p-DTS(FBTTh2)2/PC71BM BHJ solar cell up to 75.1%, one of the highest value reported for an organic solar cell. The external quantum efficiency exceeds 80%. Analysis of recombination mechanisms using the current-voltage (J-V) characteristics at various light intensities in the BHJ solar cell layer reveals that Ba prevents trap assisted Shockley-Read-Hall (SRH) recombination at the interface and with different thicknesses of the Ba, the recombination shifts towards bimolecular from monomolecular. Moreover, Ba increases shunt resistance and decreases the series resistance significantly. This results in an increase in the charge collection probability leading to high FF. This work identifies a new cathode interlayer which outclasses the all the reported interlayers in increasing FF leading to high power conversion efficiency and have significant implications in improving the performance of BHJ solar cells.
authors.affiliation: Center for Polymers and Organic Solids, University of California at Santa Barbara, Santa Barbara, California 93106-5090, USA. drvinaygupta@netscape.net
authors.forename: Vinay
authors.initials: V
authors.lastname: Gupta
authors.forename: Aung Ko Ko
authors.initials: AK
authors.lastname: Kyaw
authors.forename: Dong Hwan
authors.initials: DH
authors.lastname: Wang
authors.forename: Suresh
authors.initials: S
authors.lastname: Chand
authors.forename: Guillermo C
authors.initials: GC
authors.lastname: Bazan
authors.forename: Alan J
authors.initials: AJ
authors.lastname: Heeger