All-Polymer
Solar Cells with 3.3% Efficiency Based
on Naphthalene Diimide-Selenophene Copolymer Acceptor
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Abstract
The lack of suitable acceptor (n-type)
polymers has limited the
photocurrent and efficiency of polymer/polymer bulk heterojunction
(BHJ) solar cells. Here, we report an evaluation of three naphthalene
diimide (NDI) copolymers as electron acceptors in BHJ solar cells
which finds that all-polymer solar cells based on an NDI-selenophene
copolymer (PNDIS-HD) acceptor and a thiazolothiazole copolymer (PSEHTT)
donor exhibit a record 3.3% power conversion efficiency. The observed
short circuit current density of 7.78 mA/cm<sup>2</sup> and external
quantum efficiency of 47% are also the best such photovoltaic parameters
seen in all-polymer solar cells so far. This efficiency is comparable
to the performance of similarly evaluated [6,6]-Phenyl-C<sub>61</sub>-butyric acid methyl ester (PC<sub>60</sub>BM)/PSEHTT devices. The
lamellar crystalline morphology of PNDIS-HD, leading to balanced electron
and hole transport in the polymer/polymer blend solar cells accounts
for its good photovoltaic properties