Lowering Molecular Symmetry To Improve the Morphological Properties of the Hole‐Transport Layer for Stable Perovskite Solar Cells

Abstract

Inspired by the structural feature of the classical hole-transport material (HTM), Spiro-OMeTAD, many analogues based on a highly symmetrical spiro-core were reported for perovskite solar cells (PSCs). However, these HTMs were prone to crystallize because of the high molecular symmetry, forming non-uniform films, unfavorable for the device stability and large-area processing. By lowering the symmetry of spiro-core, we report herein a novel spirobisindane-based HTM, Spiro-I, which could form amorphous films with high uniformity and morphological stability. Compared to the Spiro-OMeTAD-based PSCs, those containing Spiro-I exhibit similar efficiencies for small area but higher ones for large area (1 cm ), and especially much higher air stability (retaining 80 % of initial PCE after 2400 h storage without encapsulation). Moreover, the Spiro-I can be synthesized from a cheap starting material bisphenol A and used with a small amount for the device fabrication.

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

“…As for FBA3, the improved lm morphology may be attributed to the fact that in comparison with FBA2, the molecular symmetry can be further destroyed due to meta-methoxy substitutions on the TPA units. 59 To test the effectiveness of these prepared uoranthene derivatives as dopant-free HTMs, a typical n-i-p planar PVSC was fabricated in a device conguration of ITO/C 60 /perovskite/ HTL/MoO 3 /Ag. The device fabrication details are described in the ESI.…”

Dopant‐Free Small‐Molecule Hole‐Transporting Material for Inverted Perovskite Solar Cells with Efficiency Exceeding 21%

“…Both SM‐HTMs show a weak π–π stacking peak either along the out‐of‐plane direction or in‐plane direction, indicating nearly amorphous nature of the MPA‐BTI and MPA‐BTTI pristine films. Nevertheless, it was found that superior film uniformity and morphological stability could be even more important than hole mobility in determining device performance of PVSCs . Based on space charge‐limited current (SCLC) method, the hole mobility of neat MPA‐BTI film is determined to be 3.99 × 10 −5 cm 2 V −1 s −1 which is comparable to that (2.13 × 10 −5 cm 2 V −1 s −1 ) of the widely used Spiro‐OMeTAD .…”

New Spiro‐Phenylpyrazole/Dibenzosuberene Derivatives as Hole‐Transporting Material for Perovskite Solar Cells

“…For deciphering this hidden factor, microscopic film morphology was investigated as it can play an important role in the overall performance of the photovoltaic application. [24a‐c] Figure shows the atomic force microscopy (AFM) topographies of HTM‐coated FTO glasses in this study. Figure a is the topographic image of spiro‐OMeTAD film; it appears homogeneous, except the observation of a few pits.…”