title: Charge carrier generation and transport in different stoichiometry APFO3:PC61BM solar cells.
abstract: In this paper we studied carrier drift dynamics in APFO3:PC61BM solar cells of varied stoichiometry (2:1, 1:1, and 1:4 APFO3:PC61BM) over a wide time range, from subpicoseconds to microseconds with a combination of ultrafast optical electric field probing and conventional transient integrated photocurrent techniques. Carrier drift and extraction dynamics are strongly stoichiometry dependent: the speed of electron or hole drift increases with higher concentration of PC61BM or polymer, respectively. The electron extraction from a sample with 80% PC61BM takes place during hundreds of picoseconds, but slows down to sub-microseconds in a sample with 33% PC61BM. The hole extraction is less stoichiometry dependent: it varies form sub-nanoseconds to tens of nanoseconds when the PC61BM concentration changes from 33% to 80%. The electron extraction rate correlates with the conversion efficiency of solar cells, leading to the conclusion that fast electron motion is essential for efficient charge carrier separation preventing their geminate recombination.
authors.affiliation: Center for Physical Sciences and Technology , Savanoriu 231, LT-02300 Vilnius, Lithuania.
authors.forename: Vytenis
authors.initials: V
authors.lastname: Pranculis
authors.forename: Yingyot
authors.initials: Y
authors.lastname: Infahsaeng
authors.forename: Zheng
authors.initials: Z
authors.lastname: Tang
authors.forename: Andrius
authors.initials: A
authors.lastname: Devižis
authors.forename: Dimali A
authors.initials: DA
authors.lastname: Vithanage
authors.forename: Carlito S
authors.initials: CS
authors.lastname: Ponseca
authors.forename: Olle
authors.initials: O
authors.lastname: Inganäs
authors.forename: Arkady P
authors.initials: AP
authors.lastname: Yartsev
authors.forename: Vidmantas
authors.initials: V
authors.lastname: Gulbinas
authors.forename: Villy
authors.initials: V
authors.lastname: Sundström