Improving the long-term stability of PBDTTPD polymer solar cells through material purification aimed at removing organic impurities
AuthorsMateker, William R.
Douglas, Jessica D.
Sachs-Quintana, I. T.
Bartelt, Jonathan A.
Hoke, Eric T.
El Labban, Abdulrahman
McGehee, Michael D.
KAUST DepartmentKAUST Solar Center (KSC)
Physical Sciences and Engineering (PSE) Division
Chemical Science Program
MetadataShow full item record
AbstractWhile bulk heterojunction (BHJ) solar cells fabricated from high M n PBDTTPD achieve power conversion efficiencies (PCE) as high as 7.3%, the short-circuit current density (JSC) of these devices can drop by 20% after seven days of storage in the dark and under inert conditions. This degradation is characterized by the appearance of S-shape features in the reverse bias region of current-voltage (J-V) curves that increase in amplitude over time. Conversely, BHJ solar cells fabricated from low Mn PBDTTPD do not develop S-shaped J-V curves. However, S-shapes identical to those observed in high Mn PBDTTPD solar cells can be induced in low M n devices through intentional contamination with the TPD monomer. Furthermore, when high Mn PBDTTPD is purified via size exclusion chromatography (SEC) to reduce the content of low molecular weight species, the JSC of polymer devices is significantly more stable over time. After 111 days of storage in the dark under inert conditions, the J-V curves do not develop S-shapes and the JSC degrades by only 6%. The S-shape degradation feature, symptomatic of low device lifetimes, appears to be linked to the presence of low molecular weight contaminants, which may be trapped within samples of high Mn polymer that have not been purified by SEC. Although these impurities do not affect initial device PCE, they significantly reduce device lifetime, and solar cell stability is improved by increasing the purity of the polymer materials. © 2013 The Royal Society of Chemistry.
SponsorsThe authors acknowledge Dr George Burkhard, Jason Bloking, and Plextronics for helpful discussions. We acknowledge the synthetic contribution of Dr Shiming Zhang in the photovoltaic polymer program at KAUST. This work was supported by the Center for Advanced Molecular Photovoltaics (CAMP) (Award no KUS-C1-015-21) made possible by the King Abdullah University of Science and Technology (KAUST). I. T. S. Q. was supported by the National Science Foundation Graduate Research Fellowship. J.A.B acknowledges additional funding from the National Defense Science and Engineering Fellowship. Additional support was provided for E. T. H. by the Fannie and John Hertz Foundation.
PublisherRoyal Society of Chemistry
JournalEnergy and Environmental Science