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Investigating the Influence of Interfacial Contact Properties on Open Circuit Voltages in Organic Photovoltaic Performance: Work Function Versus Selectivity
Author(s) -
Ratcliff Erin L.,
Garcia Andres,
Paniagua Sergio A.,
Cowan Sarah R.,
Giordano Anthony J.,
Ginley David S.,
Marder Seth R.,
Berry Joseph J.,
Olson Dana C.
Publication year - 2013
Publication title -
advanced energy materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.08
H-Index - 220
eISSN - 1614-6840
pISSN - 1614-6832
DOI - 10.1002/aenm.201200669
Subject(s) - materials science , work function , organic solar cell , open circuit voltage , heterojunction , polymer solar cell , dark current , contact resistance , saturation (graph theory) , photovoltaic system , electron , saturation current , photovoltaics , optoelectronics , solar cell , nanotechnology , voltage , composite material , electrical engineering , photodetector , polymer , mathematics , engineering , layer (electronics) , combinatorics , physics , quantum mechanics
The role of work function and thermodynamic selectivity of hole collecting contacts on the origin of open circuit voltage (V OC ) in bulk heterojunction organic photovoltaics is examined for poly(N‐9′‐heptadecanyl‐2,7‐carbazole‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole) (PCDTBT) and [6,6]‐phenyl‐C 71 butyric acid methyl ester (PC 71 BM) solar cells. In the absence of a charge selective, electron blocking contact, systematic variation of the work function of the contact directly dictates the V OC , as defined by the energetic separation between the relative Fermi levels for holes and electrons, with little change in the observed dark saturation current, J 0 . Improving the charge selectivity of the contact through an increased barrier to electron injection from the fullerene in the blend into the hole contact results in a decreased reverse saturation current (decreased J 0 and increased shunt resistance, R SH ) and improved V OC . Based on these observations, we provide a set of contact design criteria for tuning the V OC in bulk heterojunction organic photovoltaics.