Dopant‐Free Hole‐Transporting Layer Based on Isomer‐Pure Tetra‐Butyl‐Substituted Zinc(II) Phthalocyanine for Planar Perovskite Solar Cells

Abstract

Herein, the important role of the isomer purity of hole‐transporting materials (HTMs) in achieving high‐performance perovskite solar cells (PSCs) is highlighted. The isomer‐pure 2,9,16,24‐tetra‐n‐butyl‐Zn(II) phthalocyanine (RE‐ZnBu4Pc) is directly synthesized through a ring expansion method, without any further purification. The ground‐state absorption, fluorescence and thermal properties of RE‐ZnBu4Pc and the isomer mixture ZnBu4Pc, along with their hole mobilities and film morphologies are investigated, proving that RE‐ZnBu4Pc can be the more efficient HTM. The devices based on RE‐ZnBu4Pc, as dopant‐free HTMs, achieve a higher average power conversion efficiency (PCE of 11.49% ± 0.67%) and more stability at 25 °C and under 75% relative humidity than that of isomer mixture ZnBu4Pc (PCE of 9.51% ± 1.15%). RE‐ZnBu4Pc‐based PSCs also show better reproducibility in the fabrication process. This study demonstrates that better device performance can be expected for PSCs with isomer‐pure HTM materials.

Tetraphenylethylene-Arylamine Derivatives as Hole Transporting Materials for Perovskite Solar Cells

“…Nowadays, hundreds of small organic molecules, polymers, and inorganic materials have been prepared and used as HTMs in PSCs . Due to high efficiency in PSCs, well-defined structures, and smaller batch-to-batch variations, small molecules have been widely used. − The small-molecule 2,2′,7,7′-tetrakis­( N , N -di- p -methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD) derivatives still keep the highest PCE in PSCs in the published literature . However, the stiff price and low charge carrier mobility of spiro-OMeTAD limit its potential commercialized application. , Therefore, lots of alternative HTMs with different building blocks have been developed. , Among them, tetraphenylethylene-arylamine derivatives have been proven as efficient HTMs for PSCs, such as TAE-4, DBC-OMeDPA, DMZ, TPE, KR216 (Bifluo-OMeTAD), , EtheneTTPA (TAE-1, TAE, and TPE-4DPA), ,− pm-TPE-4DPA, and W2 .…”

Advancements in organic small molecule hole-transporting materials for perovskite solar cells: past and future

“…344 Variation of the central metal and peripheral substituents tunes the photo-electronic properties of phthalocyanines. [345][346][347] At the same time, adequate substitution of porphyrinoid modies the crystal packing. On the other hand, both in the solid and liquid state, the tBu-group affords good Pc solubility and minimized p-p stacking but it remains rigid.…”

Phthalocyanine in perovskite solar cells: a review

“…Recently, we compared the performance of PSCs using either a pure isomer or isomer mixture of tetra-n-butyl-substituted ZnPc as a dopant-free HTM in their structure. 91 The use of pure isomer materials in the device structure as the active layers has been confirmed as an efficient approach to achieve a higher performance and lifetime in the devices. 104,105 It has been verified that various isomers of a Pc compound can offer different values of charge carrier mobility.…”

“…The photovoltaic properties of some selected perovskite devices using tetra-substituted Pc compounds as the HTM layer are summarized in Table 2. 50,53,73–96 The molecular structures of the Pc materials used as dopant-free HTMs in PSCs are shown in Fig. 3.…”