Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Real-time x-ray scattering studies of film formation in high performing small-molecule organic solar cells



Sebastian Engmann, Felicia A. Bokel, Andrew Herzing, Hyun W. Ro, Dean DeLongchamp, Lee J. Richter, Claudio Girotto, Bruno Caputo


We have studied the influence of the additive diiodoctane on the formation dynamics of high performance bulk heterojunction (BHJ) films based the small molecule donor 7,7'-(4,4bis(2- ethylhexyl)-4H-silolo[3,2-b:4,5-b']dithiophene-2,6-diyl)bis(6-fluoro-5-(5'-hexyl-[2,2'- bithiophen]-5-yl)benzo[c][1,2,5]thiadiazaole), p-DTS(FBTTh2)2. Real-time, in-situ, grazing- incidence X-ray scattering experiments allow us to characterize both the development of crystalline order via wide angle scattering and phase separation via small angle scattering. The performance of small molecule based solar cells has been demonstrated to be extremely sensitive to the specific additive level, unlike analogous polymer systems. We find that the additive both induces increased crystallinity and coarsens the spatial scale of phase separation. The phase separation length scale varies monotonically with additive loading, suggesting the origin of the extreme sensitivity is avoiding excessive coarsening. The additive acts as both a solvent and a plasticizer, controlling the nucleation density and promoting crystal growth.
Journal of Materials Chemistry A


organic solar cell, photovolatics, fullerene, X-ray diffraction, small-angle scattering


Engmann, S. , Bokel, F. , Herzing, A. , Ro, H. , DeLongchamp, D. , Richter, L. , Girotto, C. and Caputo, B. (2015), Real-time x-ray scattering studies of film formation in high performing small-molecule organic solar cells, Journal of Materials Chemistry A, [online],, (Accessed June 18, 2024)


If you have any questions about this publication or are having problems accessing it, please contact

Created May 22, 2015, Updated October 12, 2021