Inhibited Aggregation of Lithium Salt in Spiro-OMeTAD for Perovskite Solar Cells

Guoxin Li,Ruosheng Zeng,Yukun Wang,Lixiang Huang,Wenhong Sun

doi:10.3390/cryst12020290

Abstract

High-efficiency and stable hole transport materials (HTMs) play an essential role in high-performance planar perovskite solar cells (PSCs). 2,2,7,7-tetrakis(N,N-di-p-methoxyphenylamine)-9,9-spirobi-fluorene (Spiro-OMeTAD) is often used as HTMs in perovskite solar cells because of its excellent characteristics, such as energy level matching with perovskite, good film-forming ability, and high solubility. However, the accumulation and hydrolysis of the common additive Li-TFSI in Spiro-OMeTAD can cause voids/pinholes in the hole transport layer (HTL), which reduces the efficiency of the PSCs. In order to improve the functional characteristics of HTMs, in this work, we first used CsI as a dopant to modify the HTL and reduce the voids in the HTL. A small amount of CsI is introduced into Spiro-OMeTAD together with Li-TFSI and 4-tert-butylpyridine (TBP). It is found that CsI and TBP formed a complex, which prevented the rapid evaporation of TBP and eliminated some cracks in Spiro-OMeTAD. Moreover, the uniformly dispersed TBP inhibits the agglomeration of Li-TFSI in Spiro-OMeTAD, so that the effective oxidation reaction between Spiro-OMeTAD and air produces Spiro-OMeTAD+ in the oxidation state, thereby increasing the conductivity and adjusting the HTL energy. Correspondingly, the PCE of the planar PSC of the CsI-modified Spiro-OMeTAD is up to 13.31%. In contrast, the PSC without CsI modification showed a poor PCE of 10.01%. More importantly, the PSC of Spiro-OMeTAD treated with CsI has negligible hysteresis and excellent long-term stability. Our work provides a low-cost, simple, and effective method for improving the performance of hole transport materials and perovskite solar cells.

Highlights

Research Center for Optoelectronic Materials and Devices, School of Physical Science & Technology, Guangxi Key Laboratory of Processing for Non-Ferrous Metallic and Featured Materials, School of Physical Science and Technology, MOE Key Laboratory of New Processing Technology for
The electron transport layer (SnO2 ), photosensitive layer (MAPbI3 ), and hole transport layer (Spiro-OMeTAD) are gyro-coated on patterned Indium-tin oxide (ITO) substrates successively.the device is transferred to a vacuum chamber at 2 × 10−4 Pa for electrode modified layer (MoO3 ) evaporation and electrode (Cu)
2 crystallites aremain the main reasons the degradation of perovskite solar cells this In work, found that thethat main for thefor performance degradation of solarofcells this we work, we found thereason main reason the performance degradation solaris that the surface of the hole transport layer of Spiro-OMeTAD not optimized by CsI is rough and had voids, which allows the intrusion of moisture from the air

Summary

Introduction

Research Center for Optoelectronic Materials and Devices, School of Physical Science & Technology, Guangxi Key Laboratory of Processing for Non-Ferrous Metallic and Featured Materials, School of Physical Science and Technology, MOE Key Laboratory of New Processing Technology for. 1. Introduction with regard to jurisdictional claims in Organic-inorganic hybrid perovskite has attracted much attention because of its low exciton binding energy, high absorption coefficient, wide spectral range, and long exciton diffusion length. Introduction with regard to jurisdictional claims in Organic-inorganic hybrid perovskite has attracted much attention because of its low exciton binding energy, high absorption coefficient, wide spectral range, and long exciton diffusion length It is a potential candidate material for next-generation photovoltaic devices [1,2,3,4,5,6]. Organic-inorganic hybrid lead halide perovskite solar cells (PSCs) have the characteristics of good solution processability, low cost, and high energy conversion efficiency [7,8] whicd considered to be a new generation of photovoltaic technology [9,10]. In the typical structure of PSC, the electron transport layer (ETL) and hole transport layer (HTL)

Methods

Results

Conclusion