Molecular Engineering of Copper Phthalocyanines: A Strategy in Developing Dopant‐Free Hole‐Transporting Materials for Efficient and Ambient‐Stable Perovskite Solar Cells

Abstract

production cost, simple processability, and remarkably high power conversion efficiency (PCE). [1][2][3][4] A great deal of research effort has been dedicated to the development of PSCs, including perovskite compositional engineering, advanced deposition techniques for the fabrication of high-quality perovskite films, device architecture design, and charge-selective layer optimization, as well as stability improvement etc. [5][6][7][8][9] In just a few years, the PCE of PSCs has been dramatically increased from the initial 3.8% to a certified value of over 23%, making them one of the most promising choices among low cost nextgeneration solar cell technologies. [10,11] In state-of-the-art PSCs, charge-selective contacts including hole-transporting materials (HTMs) and electron-transporting materials (ETMs) are indispensable components for achieving high PCE and high stability. [12][13][14] They play essential roles in extracting and collecting the photo-generated charge from the perovskite to the respective electrode, thus effectively reducing undesirable recombination losses at the interface and improving solar cell performance. To date, the most efficient PSCs typically utilize 2,2′,7,7′-tetrakis(N,N-di-pmethoxyphenylamine)-9,9′-spirobifluorene (Spiro-OMeTAD) Copper (II) phthalocyanines (CuPcs) have attracted growing interest as promising hole-transporting materials (HTMs) in perovskite solar cells (PSCs) due to their low-cost and excellent stability. However, the most efficient PSCs using CuPc-based HTMs reported thus far still rely on hygroscopic p-type dopants, which notoriously deteriorate device stability. Herein, two new CuPc derivatives are designed, namely CuPc-Bu and CuPc-OBu, by molecular engineering of the non-peripheral substituents of the Pc rings, and applied as dopant-free HTMs in PSCs. Remarkably, a small structural change from butyl groups to butoxy groups in the substituents of the Pc rings significantly influences the molecular ordering and effectively improves the hole mobility and solar cell performance. As a consequence, PSCs based on dopant-free CuPc-OBu as HTMs deliver an impressive power conversion efficiency (PCE) of up to 17.6% under one sun illumination, which is considerably higher than that of devices with CuPc-Bu (14.3%). Moreover, PSCs containing dopant-free CuPc-OBu HTMs show a markedly improved ambient stability when stored without encapsulation under ambient conditions with a relative humidity of 85% compared to devices containing doped Spiro-OMeTAD. This work thus provides a fundamental strategy for the future design of cost-effective and stable HTMs for PSCs and other optoelectronic devices.

An Efficient Strategy for Boosting Photogenerated Charge Separation by Using Porphyrins as Interfacial Charge Mediators

“…2.4 eV), and low onset potential. Meanwhile, porphyrins can be chosen as a mediator to maximize charge utilization as compared to previously reported photosensitizers, since they show relatively high hole mobility and it is possible to adjust their optical and electronic properties by modifying the peripheral and nonperipheral substituents and metal center …”

“…Meanwhile,p orphyrins can be chosen as am ediator to maximize charge utilization as compared to previously reported photosensitizers, [28] since they show relatively high hole mobility [29] and it is possible to adjust their optical and electronic properties by modifying the peripheral and nonperipheral substituents and metal center. [30] In this study,anovel interface charge modulation system was designed, and the resulting configuration (R-BV/CoPy/ FN-H, Figure 1a;h erein, reduced BiVO 4 ,5 ,10,15,20-tetrakis(4-carboxyphenyl)porphyrin-Co,a nd FeNi(OH) x are denoted as R-BV,C oPy,a nd FN-H, respectively) presented ah igh photocurrent of 4.75 mA cm À2 at 1.23 V( versus the reversible hydrogen electrode (RHE)) under AM 1.5 G illumination (100 mW cm À2 ). Intensity modulated photocurrent spectroscopy (IMPS) and I-t curves tests further revealed that CoPy (as the interface charge transfer mediator in the system) efficiently suppresses the interface recombination of accumulated holes with electrons,which is analogous to athe role of the volleyball setter in av olleyball match.…”

Impact of Linking Topology on the Properties of Carbazole‐Based Hole‐Transport Materials and their Application in Solid‐State Mesoscopic Solar Cells

“…After that, high PCEs of 16.91% and 18.92% were accomplished in PSCs by using the methoxydiphenylamine substituted carbazole as HTMs in 2016 and 2018, respectively, as reported by Nazeeruddin, Getautis and Snaith et al Most recently, Sellinger and Snaith et al reported PCEs over 18% and >1000 h operational stability by applying a lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)‐free carbazole‐based HTM, ET44, in PSCs . Although promising device performance in PSCs have been verified with carbazole‐based HTMs, the PCEs of related devices still cannot rival the efficiency rendered by the well‐known HTM‐Spiro‐OMeTAD (2,2′,7,7′‐tetrakis‐( N , N ‐di‐ p ‐methoxy‐phenyl‐amine)9,9′‐spirobifluorene) in PSCs . Particularly, the fundamental understanding of the impact of linking topology on the properties of carbazole‐based HTMs is lacking, and such knowledge is vital for future design concepts for even more efficient carbazole‐based HTMs for the application in high‐performance ssMSCs.…”

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

“…Metal phthalocyanines (MPcs) are highly thermal, chemical, and photostable p ‐type semiconductors, with intense absorption in the near‐infrared region, and are intensely used in thin‐film transistors and organic solar cells, which make them an interesting class of HTMs for PSCs . These low‐cost materials also offer relatively high hole mobility and high hydrophobicity . MPc's special properties can be adjusted by introducing various peripheral and nonperipheral substitutions with different electronic and spatial properties, as well as changing metal centers to control their structural and energetic features .…”

“…Sun and co‐workers introduced 4‐butylphenoxy and 4‐butoxyphenoxy groups as nonperipheral substituents to CuPc, and the isomer mixtures of CuPc‐Bu and CuPc‐OBu materials are prepared and used as dopant‐free HTMs in PSCs . They have reported PCEs of 14.3% and 17.6% for remarkably stable devices based on CuPc‐Bu and CuPc‐OBu HTMs, respectively.…”