Abstract
Detailed analyses of the microstructures of bulk-heterojunction (BHJ) layers are important for the development of high-performance photovoltaic organic solar cells (OSCs). However, analytical methods for BHJ layer microstructures are limited because BHJ films are composed of a complex mixture of donor and acceptor materials. In our previous study on the microstructure of a BHJ film composed of donor polymers and fullerene-based acceptors, we analyzed donor polymer-only films after selectively extracting fullerene-based acceptors from the film by atomic force microscopy (AFM). Not only was AFM suitable for a clear analysis of the morphology of the donor polymers in the BHJ film, but it also allowed us to approximate the acceptor morphology by analyzing the pores in the extracted films. Herein we report a method for the selective extraction of nonfullerene acceptors (NFAs) from a BHJ layer in OSCs and provide a detailed analysis of the remaining BHJ films based upon AFM. We found that butyl glycidyl ether is an effective solvent to extract NFAs from BHJ films without damaging the donor polymer films. By using the selective extraction method, the morphologies of NFA-free BHJ films fabricated under various conditions were studied in detail. The results may be useful for the optimization of BHJ film structures composed of NFAs and donor polymers.
Highlights
Organic solar cells (OSCs) have undergone tremendous development in recent years thanks to features that have enabled them overcome the limitations found in their inorganic counterparts, the most notable of which are light weight, possible incorporation into flexible devices, and roll-to-roll processing, with the potential of low-cost mass production of power generation devices [1,2,3]
To apply the selective extraction method and the subsequent atomic force microscopy (AFM) observation to OSCs based on NFAs and donor polymers, we first tested various organic solvents, such as n-hexane, N,N-dimethylformamide (DMF), tetrahydrofuran (THF), dichloromethane (DCM), diethyl ether (Et2O), butyl glycidyl ether (BGE), toluene, and pyridine, for their ability to selectively extract EH-IDTBR from donor/acceptor blend films composed of EH-IDTBR and PTB7:ITIC-based films (PTB7) ((weight of donor: D)/(total weight: D + A) = 0.50)
PBDB-T does not dissolve in BGE, and BGE washing did not affect the morphology of the PBDB-T thin films (Figure S3c,d), which indicated that the selective extraction of EH-IDTBR takes place in BHJ films composed of PBDB-T
Summary
Organic solar cells (OSCs) have undergone tremendous development in recent years thanks to features that have enabled them overcome the limitations found in their inorganic counterparts, the most notable of which are light weight, possible incorporation into flexible devices, and roll-to-roll processing, with the potential of low-cost mass production of power generation devices [1,2,3]. To fabricate an effective BHJ structure in films with the above features, detailed analyses of BHJ film microstructures are imperative to yield efficient OSCs with high photovoltaic performance To this end, X-ray measurement, electron microscopy, and other special measurements are usually used. To study the BHJ layer microstructure, the selective extraction method [14,15] has been adopted, by which donor polymer-only films are obtained after the extraction of small molecular acceptors from the donor/acceptor blend films (Figure 1b) Using this method, the morphology of donor materials in BHJ films can be observed by atomic force microscopy (AFM). Lou waUpidSreeAlcyu)ru.ssToerhdfeoforirnthOdeSiueClmedcetrtvoiinncetosr,axzniidsnpceoa(rcIteiTntyOglal)acyseuetorbnfisalttmrea,htayendsdr(apstoehl(ye9(e93t.,94r9-ee5ts%hisy, ttleraanncecedemio=xety1atl0hsiΩobpashsiesqn))eaa)s:nd Au pwoleyr(4e-sptyurrecnhe asuslefdonfartoe)m(PEthDeOFT:uPrSuS)u(cChleivCiohsePm) aiscaalmCatoerrpiaol froarthioonle (trTaonkspyoort,inJagplaayne)r These materials were purchased from 1-Material Inc.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
