Molecular Doping for Hole Transporting Materials in Hybrid Perovskite Solar Cells

Vanira Trifiletti,Norberto Manfredi,Silvia Colella,Thibault Degousée,Aurora Rizzo,Oliver Fenwick

doi:10.3390/met10010014

Abstract

Hybrid lead halide perovskites have been revolutionary in the photovoltaic research field, reaching efficiencies comparable with the most established photovoltaic technologies, although they have not yet reached their competitors’ stability. The search for a stable configuration requires the engineering of the charge extraction layers; in this work, molecular doping is used as an efficient method for small molecules and polymers employed as hole transport materials in a planar heterojunction configuration on compact-TiO2. We proved the viability of this approach, obtaining significantly increased performances and reduced hysteresis on compact titania-based devices. We investigated the photovoltaic performance correlated to the hole transport material structure. We have demonstrated that the molecular doping mechanism is more reliable than oxidative doping and have verified that molecular doping in polymeric hole transport materials leads to highly efficient perovskite solar cells, with long-term stability.

Highlights

Hybrid lead halide perovskites are revolutionary materials for a wide range of optoelectronic and electronic applications [1,2,3]
Spiro-OMeTAD has given excellent results—the doping occurs by the oxidation of the complex that it forms with the additive lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in an open system condition
We can conclude that p-type molecular doping by careful tuning of the dopant weight per cent is promising in enhancing the photovoltaic performance of perovskite cells

Summary

Introduction

Hybrid lead halide perovskites are revolutionary materials for a wide range of optoelectronic and electronic applications [1,2,3]. In the photovoltaic research field, they have shown efficiencies comparable with the most established photovoltaic technologies, overcoming the thin-film technologies, perovskite-based solar cells have not yet reached their competitors’ stability [1,4,5,6]. A step towards achieving devices with long-term stability has recently been achieved with mixed-cation lead mixed-halide perovskites, such as (HC(NH2 )2 )0.83 Cs0.17 Pb(I0.6 Br0.4 )3 [7,8]. In conventional device architecture (substrate, cathode, electron transporting material (ETM), hybrid perovskite, hole transporting material (HTM), anode), the most commonly employed HTM, due to its significant solubility and excellent hole mobility, is Spiro-OMeTAD ((2,20 ,7,70 -Tetrakis N, N-di-p-methoxyphenylamine)-9,90 -spirobifluorene) [10,11]. It is hard to collect consistent results, because the amount of oxidised

Methods

Results

Conclusion