Journal
ADVANCED MATERIALS
Volume 34, Issue 50, Pages -Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/adma.202206717
Keywords
fused-ring electron acceptor; nonfullerene; organic solar cell; quasi-homojunction
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Funding
- NSFC [21875182, U21A20101, 21734001, 52103219]
- China Postdoctoral Science Foundation [2017M612199]
- Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy [DE-AC02-05CH11231]
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In contrast to classical bulk heterojunction (BHJ) in organic solar cells (OSCs), the quasi-homojunction (QHJ) with extremely low donor content (<= 10 wt.%) is unusual and generally yields much lower device efficiency. However, by selecting appropriate polymer donors and nonfullerene acceptors, high-efficiency QHJ devices can be fabricated by generating free charges in the acceptor domains.
In contrast to classical bulk heterojunction (BHJ) in organic solar cells (OSCs), the quasi-homojunction (QHJ) with extremely low donor content (<= 10 wt.%) is unusual and generally yields much lower device efficiency. Here, representative polymer donors and nonfullerene acceptors are selected to fabricate QHJ OSCs, and a complete picture for the operation mechanisms of high-efficiency QHJ devices is illustrated. PTB7-Th:Y6 QHJ devices at donor:acceptor (D:A) ratios of 1:8 or 1:20 can achieve 95% or 64% of the efficiency obtained from its BHJ counterpart at the optimal D:A ratio of 1:1.2, respectively, whereas QHJ devices with other donors or acceptors suffer from rapid roll-off of efficiency when the donors are diluted. Through device physics and photophysics analyses, it is observed that a large portion of free charges can be intrinsically generated in the neat Y6 domains rather than at the D/A interface. Y6 also serves as an ambipolar transport channel, so that hole transport as also mainly through Y6 phase. The key role of PTB7-Th is primarily to reduce charge recombination, likely assisted by enhancing quadrupolar fields within Y6 itself, rather than the previously thought principal roles of light absorption, exciton splitting, and hole transport.
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