Novel N-Type π-Conjugated Polymers for All-Polymer Solar Cell

solar cell;photovoltaics;organic chemistry

He, Yinghuiadvisor:Bassani, Dario ; affiliation1:Faculty of Engineering ; advisor:Li, Yuning ; Li, Yuning ; Bassani, Dario ;

University of Waterloo

关键词: organic chemistry;    Doctoral Thesis;    solar cell;    photovoltaics;   

Others  :  https://uwspace.uwaterloo.ca/bitstream/10012/12466/3/He_Yinghui.pdf

瑞士|英语

来源: UWSPACE Waterloo Institutional Repository

【 摘 要 】

Organic solar cells (OSCs), also known as, organic photovoltaics (OPVs), appear as a promisingtechnology for renewable energy owing to their light weight, great flexibility and low-cost fabricationprocess. So far most of the OPVs have been using fullerene derivatives, such as PCBM or PC71BM,as the electron acceptor in the active layer, which have been proven to a bottleneck for this technology.Therefore, developing non-fullerene acceptors has become the new driving force for this field. Allpolymersolar cells (all-PSCs) that have the advantages of robustness, stability and tunability havealready achieved PCE up to 9%. However, there is still a significant gap between the all-PSCs andfullerene-based OSCs (PCE approaching 12%) despite tremendous effort that has been put into theoptimization of both material and device. Thus, developing novel acceptor materials is imperative forimproving the performance of all-PSCs. In this thesis, three classes of π-conjugated polymers weredesigned and synthesized for the application of all-PSC. The first class of polymers is based on an novelelectron-deficient moiety, (3E,7E)-3,7-bis(2-oxoindolin-3-ylidene)-5,7-dihydropyrrolo[2,3-f]indole-2,6(1H,3H)-dione (IBDP). The IBDP-based polymers (P1 and P2) showed balanced ambipolartransport property (electron mobility up to 0.10 cm2 V-1 s-1 and hole mobility up to 0.19 cm2 V-1 s-1) inOTFTs. In addition to the good charge transport properties, the IBDP polymers exhibited strong andbroad adsorption profile across the visible and NIR region up 1100 nm as well as elevated LUMO levelsat -3.70 eV. With these advantageous features, these IBDP polymers were used as acceptor with poly(3-hexylthiophene-2,5-diyl) (P3HT) as the donor in all-PSCs. After donor/acceptor ratio optimization, theresultant all-PSC devices showed high PCE of 3.38%, which is the highest PCE that has been obtainedfrom P3HT-based all-PSCs so far. The second class consists of three (3E,7E)-3,7-bis(2-oxoindolin-3-ylidene)benzo[1,2-b:4,5-b’]difuran-2,6(3H,7H)-dione (IBDF)-based polymers that feature a new typeof side chains that contain an ester group. The resultant IBDF polymers exhibited excellent electrontransport properties with electron mobility up to 0.35 cm2 V-1 s-1 in OTFTs. When used as acceptor in all-PSCs with PTB7-Th as donor, low PCEs (<0.4%) were obtained, which was found to be caused bythe poor miscibility of the donor and acceptor, as well as the inferior bulk charge transport propertiesof the IBDF polymers. Finally, a new building block, dihydroxylnaphthalene diimide (NDIO), wasintroduced for the first time into π-conjugated polymers. Due to the alkoxy groups, the electron affinityof the NDIO polymer is significantly higher than the NDI analogues, which led to an enhanced electrontransport property and more stable performance in OTFTs upon air-exposure. When used as acceptorin all-PSCs with PTB7-Th as the donor, a decent PCE of 3.25 % was realized. In particular, the FF(0.61) of the solar cell devices is much higher than those of the NDI polymers based all-PSCs, whichwas attributed to the balanced charge transport for both hole and electron in the active layer, as well asthe suppressed bimolecular recombination.