Investigating the Molecular Orientation and Thermal Stability of Spiro‐OMeTAD and its Dopants by Near Edge X‐Ray Absorption Fine Structure

• DOI: 10.1002/apxr.202200045
• Publication Date: 2023-04-22T10:59:11Z
• Authors: Anita Brady‐Boyd; Kerry Hazeldine; Rachel E. Cross; Gongxizi Ren; Arthur Connell; Christopher P. Ke...; Peter J. Holliman; D. Andrew Evans
• Keywords: Thermal Stability; XANES; Absorption edge; Tetracyanoquinodimethane

Abstract This study describes the utilization of near edge X‐ray absorption fine structure (NEXAFS) to investigate hole transporting material (HTM) 2,2ʹ,7,7ʹ‐tetrakis( N , ‐di‐ p ‐methoxyphenylamine)‐ 9,9ʹ‐spirobifluorene (Spiro‐OMeTAD) and its most common dopants, lithium bis‐(trifluoromethylsulfonyl) imide (LiTFSI), 4‐ tert ‐butylpiridine ( t BP), 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4‐TCNQ). By changing angle sample with respect beam, orientation molecules on surface can be observed. The data suggest that it is difficult determine any orientational preference for Spiro‐OMeTAD deposited a due 3D propeller‐like geometry this molecule. Both doped undoped samples show thermal stability beyond glass transition temperature molecules. Significant changes spectra are observed addition in particular C K‐edge. Differences also valence band when dopants added. It demonstrated how doping combination LiFTSI BP and, F4‐TCNQ act as p‐type by altering position HOMO levels. induces larger change levels compared LiTFSI BP. These results important increase understanding effect have next generation solar cells.