Interfacial and bulk properties of hole transporting materials in perovskite solar cells: spiro-MeTAD versus spiro-OMeTAD

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2020, Vol.8 (17), p.8527-8539
• Main Authors: Sallenave, Xavier, Shasti, Mona, Anaraki, Elham Halvani, Volyniuk, Dmytro, Grazulevicius, Juozas Vidas, Zakeeruddin, Shaik M, Mortezaali, Abdollah, Grätzel, Michael, Hagfeldt, Anders, Sini, Gjergji
• Format: Article
• Language: English
• Subjects: Chemical Sciences
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/D0TA00623H

Two spiro-MeTAD compounds (1 and 2) were synthesized, characterized by experimental and quantummechanical methods, and used as hole transporting materials (HTMs) in perovskite solar cells (PSCs). Thenew compounds differ from spiro-OMeTAD only by the presence of methyl substituents as compared tomethoxy groups. This modification results in the absorption band blue shifting by 20 nm as comparedto spiro-OMeTAD, increased glass transition temperature for 2, and reduced ionization potentials by0.02–0.12 eV. Hole mobilities five times larger were obtained for spiro-MeTAD/spiro-MeTAD, which ismaintained in the presence of additives. Despite this improvement, J–V measurements in PSCs resultedin a power conversion efficiency (PCE) of 17.2% and 17.05% for 1 and 2 HTMs, respectively, as comparedto 19.24% for spiro-OMeTAD. Photoluminescence measurements of perovskite:HTM layers indicatemuch stronger quenching in the case of spiro-OMeTAD/spiro-MeTAD. These results point to thedominant importance of the perovskite:HTM interfacial properties as compared to the HTM holetransport properties in the bulk. Given that improved hole-mobility and energy-level alignment are themain targets of the current research efforts in this domain, our results alert to the necessity to prioritizethe improvement of perovskite–HTM interaction properties.