Influence of functionalized fullerene structure on polymer photovoltaic degradation

Abstract

a b s t r a c tThe time dependence of device performance has been measured for photocells using blends containing the conjugated polymer, poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) with two different functionalized C 60 electron acceptor molecules: commercially available [6,6]-phenyl C 61 butyric acid methyl ester (PCBM) or [6,6]-phenyl C 61 butyric acid octadecyl ester (PCBOD) produced in this laboratory. Performance was characterized by the short-circuit current output of the devices, with the time dependence of PCBM samples typically degrading exponentially. Variations in the characteristic lifetime of the devices were observed to depend on the molar fraction of the electron acceptor molecules (calculated with respect to the MEH-PPV monomer fraction). In comparison to the PCBM samples, the stability of the PCBOD blends was significantly enhanced, with a one or two order of magnitude improvement. Corresponding spectroscopic data with similar time evolution as the transport measurements suggest an independent means for determining and understanding degradation mechanisms.

Stability of Polymer Solar Cells

“…[109] stability. [121] Comparing the standard C 61 -butyric acid methyl ester (PCBM) with the longer chain analogue C 61 butyric acid octadecyl ester (PCBOD) they found a slower initial decay of the efficiency with the latter acceptor compound.…”

Effects of amorphous poly(3‐hexylthiophene) on active‐layer structure and solar cells performance

“…24,25 There is a threshold concentration for PCBM to dissolve in the interlamellar amorphous P3HT regions, above which a phase separation occurs and the aggregates may be in a scale larger than the exciton diffusion length so that efficiency decreases accordingly. 2 Many efforts have been made to retard the phase separation in polymer/fullerene blends so as to enhance the stability of devices, including the crosslinking of polymer to fix the structure, 26,27 the chemical modification of fullerene to lower the diffusion rate, [28][29][30] and the incorporation of additives or functional groups to enhance the miscibility between polymer and fullerene. 31,32 In addition, an increase of the amorphous fraction of polymer has been shown to be a strategy to efficiently improve the stability.…”

Structure-function relationships of fullerene esters in polymer solar cells: unexpected structural effects on lifetime and efficiency

“…Sample fabrication is described in previous work [22] and briefly summarized here. Indium Both spectroscopic and transport experiments are carried out for periods of hours or days.…”

“…In previous experiments in our laboratories alternative electron acceptors were synthesized including [6,6]-phenyl C 61 butyric acid octadecyl ester (PCBOD, 1a) [22] and [6,6]-phenyl C 61 butyric acid octyl ester (PCBO, 1b) [23] ( Figure 1). Based on detailed results for PCBOD and preliminary ones for PCBO, we have produced a more diverse set of PCB-alkyl esters and measured the figures of merit for photovoltaic devices using these additives.…”

“…For the electron donor (in this expression P3HT), we use the monomer molar mass. In other words, x = 0.5 represents a blend with one C 60 molecule per P3HT monomer [22][23][24]. Notation in the literature often uses weight concentrations.…”