Precise Control of Thermal and Redox Properties of Organic Hole‐Transport Materials

Abstract

We report design principles of the thermal and redox properties of synthetically accessible spiro-based hole transport materials (HTMs) and show the relevance of these findings to high-performance perovskite solar cells (PSCs). The chemical modification of an asymmetric spiro[fluorene-9,9'-xanthene] core is amenable to selective placement of redox active triphenylamine (TPA) units.W etherefore leveraged computational techniques to investigate five HTMs bearing TPAgroups judiciously positioned about this asymmetric spiro core.Itwas determined that TPAg roups positioned about the conjugated fluorene moiety increase the free energy change for holeextraction from the perovskite layer,w hile TPAs about the xanthene unit govern the T g values.T he synergistic effects of these characteristics resulted in an HTM characterized by both al ow reduction potential ( % 0.7 Vv s. NHE) and ah igh T g value (> 125 8 8C) to yield adevice power conversion efficiency (PCE) of 20.8 %inaP SC.

Efficiencyvs.stability: dopant-free hole transporting materials towards stabilized perovskite solar cells

“…It was determined that TPA groups positioned about the conjugated fluorene moiety increase the free energy change for hole-extraction from the perovskite layer, while TPAs about the xanthene unit govern the T g values and hole mobility. 4-fold HTM-FX and HTM-FX’ exhibited PCEs of 19.5% and 20.8%, respectively 94. Recently, the fluorene-terminated spiro-OMeTAD alternative DM has been reported to have achieved a record efficiency of 23.2% so far.…”

Cut from the Same Cloth: Enamine-Derived Spirobifluorenes as Hole Transporters for Perovskite Solar Cells

“… 17 Several groups have studied central 9,9′spirobifluorene-linked HTMs including dimethylfluorenyl-, ethylcarbazolyl-, and fluorinated methoxyphenyl-terminated compounds, which have been recently reported by Seo, 18 Chen, 19 and Yang, 20 respectively. However, the main focus is still directed on the development of new central spiro-cored structures such as spiro[fluorene-9,9′-xanthene], 21 − 25 spirobisacridine, 26 thiophene-containing spiro cores, 27 − 29 and other spiro-type derivatives. 30 , 31 However, the peripheral part is equally or of even more importance in fine tuning the properties of the HTM.…”

Recent Advances in Organic Hole Transporting Materials for Perovskite Solar Cells

“…Another interesting exploration was focusing on the structural design on thermal and electrochemical behaviors of the spiro[fluorene-9,9 0 -xanthene] (SFX)-based HTMs bearing TPA groups by associated simple reaction chemistry. [60] A remarkable change in hole extraction and electrochemical redox properties by more than 300 eV occurs as a result of the linking TPA groups to the conjugated fluorene moiety. Whereas TPA pending group to the xanthene unit enhances the hole mobility and increases the T g values by more than 30 C. Fourfold HTM-FX and HTM-FX 0 exhibited PCEs of 19.5% and 20.8%, respectively.…”