Low‐Cost N,N′‐Bicarbazole‐Based Dopant‐Free Hole‐Transporting Materials for Large‐Area Perovskite Solar Cells

Abstract

Despite the recent unprecedented development of efficient dopant‐free hole transporting materials (HTMs) for high‐performance perovskite solar cells (PSCs) on small‐area devices (≤0.1 cm2), low‐cost dopant‐free HTMs for large‐area PSCs (≥1 cm2) with high power conversion efficiencies (PCEs) have rarely been reported. Herein, two novel HTMs, 3,3′,6,6′ (or 2,2′,7,7′)‐tetrakis(N,N′‐di‐p‐methoxyphenylamine)‐N,N′‐bicarbazole (3,6 BCz‐OMeTAD or 2,7 BCz‐OMeTAD), are synthesized via an extremely simple route from very cheap raw materials. Owing to their excellent film‐forming abilities and matching energy levels, 3,6 BCz‐OMeTAD and 2,7 BCz‐OMeTAD can be successfully employed as a perfect ultrathin (≈30 nm) hole transporting layer in large‐area PSCs up to 1 cm2. The 3,6 BCz‐OMeTAD and 2,7 BCz‐OMeTAD based large‐area PSCs show highest PCEs up to 17.0% and 17.6%, respectively. More importantly, high performance large‐area PSCs based on 2,7 BCz‐OMeTAD retain 90% of the initial efficiency after 2000 h storage in an ambient environment without encapsulation.

A structure–property study of fluoranthene-cored hole-transporting materials enables 19.3% efficiency in dopant-free perovskite solar cells

“…[29][30][31] On the other hand, the branched structure has also been successfully adopted in designing efficient dopant-free HTMs. [35][36][37][38][39] By integrating these two molecular strategies, Nazeeruddin et al developed a new class of star-shaped D-A type dopant-free HTMs using quinolizino acridine (FA) and triazatruxene as the core moiety to yield a high PCE of 19.03%. 40,41 Note that, despite these achievements, all of those top-performing dopant-free HTMs developed so far are derived from complicated p-conjugated scaffolds requiring tedious synthesis and purication, such as BDT, [25][26][27][28][29][30][31] quinolizino acridine (FA), 40 triazatruxene 41 and so on, making their synthetic costs too high to be used for widespread applications.…”

LiTFSI‐Free Spiro‐OMeTAD‐Based Perovskite Solar Cells with Power Conversion Efficiencies Exceeding 19%

“…Novel additives, such as H 3 PO 4 [28] and fluorine-containing Lewis acid, [29] are also employed to enhance the HTM conductivity while reducing the hysteresis in devices due to the lack of extrinsic ion migration such as Li ion. [31][32][33] Another approach is the use of dicationic salts of spiro-OMeTAD, the mechanism of which is shown in Equation (3) [34,35] spiro-OMeTAD spiro-OMeTAD 2 spiro-OMeTAD 2 + → + + [18,30] The by-products of the oxidation, such as reduced metal cations and counter ions, remain as impurities in the final devices with still undetermined effects on device performance.…”

Hole Transport Materials in Conventional Structural (n–i–p) Perovskite Solar Cells: From Past to the Future

“…The Z1011 device exhibited a higher stability at room temperature in dry air without encapsulation when compared to the spiro‐OMeTAD device by maintaining over 50% of its initial efficiency after 1008 h. The Z1013 device even exhibited a higher thermal stability. Per‐SC employing 2,7‐BCz‐OMeTAD based on N , N ′‐bicarbazole exhibited high efficiency even in large‐area devices of up to 1 cm 2 . Bicarbazole possesses versatile and easily tunable optoelectronic properties and provides rigidity and steric hindrance caused by its perpendicular twisted structures, like spiro‐OMeTAD, which leads to high T g .…”