A unified description of current-voltage characteristics in organic and hybrid photovoltaics under low light intensity.
We develop a simple model that can explain the current-voltage ( J- V) curves of excitonic photovoltaic solar cells, spanning polymer:polymer, polymer:fullerene, and polymer:nanocrystal devices. We show that by subtracting out the dark current, we can explain apparent intensity-dependent characteristics and thus identify geminate recombination as the dominant loss mechanism and establish its electric field dependence. We present an analytic fit to the J- V curves of all measured devices based on a single fitted parameter, the electric field required to split 50% of geminate charge pairs, which we term the critical field. Devices of different material combinations and morphologies can all be described by this method and yield critical fields varying between >1 x 10(8) V/m for blends of poly(9,9'-dioctylfluorene- co-bis- N, N'-(4-butylphenyl)-bis- N, N'-phenyl-1,4-phenylenediamine) (PFB) and poly(9,9'-dioctylfluorene- co-benzothiadiazole) (F8BT) and 8 x 10 (5) V/m for slow-grown blends of poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). A comparison with material properties reveals that the primary route to improved photovoltaic materials is enhanced charge delocalization.
Marsh
R A
RA
Cavendish Laboratory, J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom. ram47@cam.ac.uk
McNeill
C R
CR
Abrusci
A
A
Campbell
A R
AR
Friend
R H
RH
D003198:Computer Simulation; D004553:Electric Conductivity; D011211:Electric Power Supplies; D004563:Electrochemistry / Q000295:instrumentation* / Q000379:methods; D004867:Equipment Design; D019544:Equipment Failure Analysis; D037741:Fullerenes / Q000737:chemistry* / Q000528:radiation effects; D008027:Light; D008962:Models, Theoretical; D010777:Photochemistry / Q000295:instrumentation* / Q000379:methods; D011108:Polymers / Q000737:chemistry / Q000528:radiation effects; D011829:Radiation Dosage
D037741:Fullerenes; D011108:Polymers