Tantalum Oxide as an Efficient Alternative Electron Transporting Layer for Perovskite Solar Cells.

Meenal Deo,Alexander Möllmann,Daniel Stadler,Sanjay Mathur,Jinane Haddad,Ashish Kulkarni,Tim Ludwig,Feray Ünlü,Aman Bhardwaj,Yasuhiro Tachibana,Maning Liu,Thomas Kirchartz

doi:10.3390/nano12050780

Abstract

Electron transporting layers facilitating electron extraction and suppressing hole recombination at the cathode are crucial components in any thin-film solar cell geometry, including that of metal–halide perovskite solar cells. Amorphous tantalum oxide (Ta2O5) deposited by spin coating was explored as an electron transport material for perovskite solar cells, achieving power conversion efficiency (PCE) up to ~14%. Ultraviolet photoelectron spectroscopy (UPS) measurements revealed that the extraction of photogenerated electrons is facilitated due to proper alignment of bandgap energies. Steady-state photoluminescence spectroscopy (PL) verified efficient charge transport from perovskite absorber film to thin Ta2O5 layer. Our findings suggest that tantalum oxide as an n-type semiconductor with a calculated carrier density of ~7 × 1018/cm3 in amorphous Ta2O5 films, is a potentially competitive candidate for an electron transport material in perovskite solar cells.

Highlights

IntroductionPublisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations
A reference device was fabricated without any blocking layer (Ta0) to show the beneficial effect of adding tantalum oxide to an electron transporting layer (ETL)
We have demonstrated the incorporation of thin amorphous Ta2 O5 interfacial layers as alternative ETLs in perovskite solar cells to replace the commonly used TiO2 blocking layer

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. ETLs that combine high photostability and good electronic compatibility among functional components (ETL, HTL, photo absorber) with low defect densities at the ETL/perovskite interface In this context, tantalum oxide is one of the yet unexplored but potentially promising materials owing to its high transparency, chemical stability and favorable band alignment with perovskite, as demonstrated in this study for a triple-cation mixed-halide perovskite (Cs0.05 (MA0.17 FA0.83 )(0.95) Pb(I0.83 Br0.17 ) ). Employed Ta2 O5 as a passivation layer between mesoporous TiO2 and perovskite layers and observed an increase in open circuit voltage, leading to better performances Despite these efforts, Ta2 O5 has not been explored in all dimensions, emphasizing both the potential and the necessity for further investigation in this field. This was further corroborated by steady-state photoluminescence (PL) measurements demonstrating efficient electron injection from perovskite to the thin Ta2 O5 layer

Deposition of Ta2 O5 Films and Fabrication of Perovskite Solar Cells

Deposition of Ta2O5 Films and Fabrication of Perovskite

Characterization of Deposited Ta

Results and Discussion

O5 filmsatannealed

Conclusions