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processed a family of new squaraine donor materials.<br />
The interplay of J sc , V oc and FF determines the final efficiency. V oc depends on the<br />
energy offset at the donor/acceptor interface, which can be improved by tuning and<br />
designing new squaraine donor materials. J sc is enhanced through understanding the<br />
energy harvesting process and shifting the absorption spectrum into longer<br />
wavelengths. High FF is achieved through controlling the charge collection process<br />
and building new device architectures.<br />
In this introductory chapter, we have discussed the basic principles of organic<br />
solar cells on how to efficiently convert photons into free carriers. Two different<br />
organic solar cell structures have been introduced and their comparison was<br />
discussed. The past progress on solution-processed organic solar cells has implied the<br />
importance of the donor material choice to improve device performance. Our goals in<br />
this work are to (1) explore new squaraine donor materials; (2) explore novel device<br />
architectures for efficiency improvement; (3) understand the correlation between<br />
molecular structure and device performance.<br />
In Chapter 2, we examine squaraine device performance employing SQ:PC 70 BM<br />
and SQ:PC 60 BM bulk HJ structures, in comparison with SQ/C 70 and SQ/C 60 planar<br />
HJ structures. This result indicates that the nanoparticle morphology introduces<br />
internal resistance into the solution-based SQ:PC 70 BM and SQ:PC 60 BM blend thin<br />
films. The distribution of the SQ donor nanoparticles in the acceptor matrix as a<br />
function of relative concentration results in a trade-off between exciton dissociation<br />
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