Boosting Organic Solar Cell Electrical Performance by Introducing Large Aromatics onto Small‐Molecule Peripheral Side‐Chains. Issue 17 (28th June 2016)

• Record Type: Journal Article
• Authors: Zhang, Xinliang; Yao, Jiannian; Zhan, Chuanlang
• Is Part Of: Advanced materials interfaces. Volume 3:Issue 17(2016)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2016-06-28
• Subjects: bulk‐heterojunction -- diketopyrrolopyrrole -- organic solar cells -- small‐molecules -- structure‐performance relationship; Materials science -- Periodicals; 620.11
• DOI: 10.1002/admi.201600323
• Languages: English
• ISSNs: 2196-7350

Abstract

Abstract : It is reported herein that electrical performance of diketopyrrolopyrrole based small‐molecule solar cells are boosted via increasing the conjugation size fraction ( δ ) on lateral side‐chains and on the mainchain of small‐molecule donor. The conjugation size fraction is defined as δ = N p / N m, where N p is the number of five‐ or six‐member aromatic rings on the peripheral side‐chains and N m is that on the mainchain. As the DPP‐dimer's core structure varies from 5, 10‐bis((5‐(2‐ethylhexyl)thiophen‐2‐yl)dithieno[2, 3‐ d :2′, 3′‐ d ′]benzo[1, 2‐ b :4, 5‐ b ′]dithiophene (DT ‐BDT ) to 4, 8‐bis((5‐(2‐ethylhexyl)thiophen‐2‐yl)‐BDT (2T ‐BDT ), and then 4, 8‐bis(5′‐(2‐ethylhexyl)‐(2, 2′‐bithiophen)‐5‐yl)‐BDT (4T ‐BDT ), the term of δ increases from 2/13 to 2/11 and then 4/11. In the blended film with the fullerene acceptor, the donor phase size decreases from 35 to 24 and 15 nm, becoming more and more approaching to the effective exciton diffusion length. Consequently, the obtainable maximum generation rate of electron–hole bound pairs increases from 7.0 × 10 27 to 7.3 × 10 27 and then 7.7 × 10 27 m −3 s −1 . Meanwhile, reduction of donor crystallinity with the increase of δ leads to a higher effective carrier mobility, which suppresses recombination losses and leads to a larger carrier collection probability. Promotions of both charge separation and transport give a larger short‐circuit current density, a higher fill‐factor, and ultimately a larger efficiency. Abstract : Relative size of conjugation systems on lateral side‐chains relative to that on the mainchain of a small molecule donor is found to be a structural factor that effectively tunes donor phase size and molecular crystallinity, and consequently on small‐molecule organic solar cell performance.