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Centimetre-scale perovskite solar cells with fill factors of more than 86 per cent

Nature volume 601, pages 573–578 (2022)Cite this article

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Abstract

Owing to rapid development in their efficiency1 and stability2, perovskite solar cells are at the forefront of emerging photovoltaic technologies. State-of-the-art cells exhibit voltage losses3,4,5,6,7,8 approaching the theoretical minimum and near-unity internal quantum efficiency9,10,11,12,13, but conversion efficiencies are limited by the fill factor (<83%, below the Shockley–Queisser limit of approximately 90%). This limitation results from non-ideal charge transport between the perovskite absorber and the cell’s electrodes5,8,13,14,15,16. Reducing the electrical series resistance of charge transport layers is therefore crucial for improving efficiency. Here we introduce a reverse-doping process to fabricate nitrogen-doped titanium oxide electron transport layers with outstanding charge transport performance. By incorporating this charge transport material into perovskite solar cells, we demonstrate 1-cm2 cells with fill factors of >86%, and an average fill factor of 85.3%. We also report a certified steady-state efficiency of 22.6% for a 1-cm2 cell (23.33% ± 0.58% from a reverse current–voltage scan).

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Fig. 1: XPS characterization of TiOxNy films annealed at different temperatures.
Fig. 2: TEM characterization and simulation of the diffraction pattern.
Fig. 3: Optoelectronic properties of TiOxNy films annealed at different temperatures.
Fig. 4: Device characterization and simulation.

Data availability

The data that support the findings of this study are available from the corresponding authors on reasonable request.

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Acknowledgements

This work was supported by the Australian Government through the Australian Renewable Energy Agency and the Australian Research Council. Responsibility for the views, information or advice expressed herein is not accepted by the Australian Government. J.P. acknowledges the financial support of a Postdoc Fellowship from the Australian Centre for Advanced Photovoltaics. T.P.W. is the recipient of an Australian Research Council Future Fellowship (project number FT180100302) funded by the Australian Government. T.P.W. also acknowledges the support of the Open Fund of the State Key Laboratory of Optoelectronic Materials and Technologies (Sun Yat-sen University). D.Z. acknowledges funding from the National Natural Science Foundation of China (grant numbers 11574403 and 11974431). The work was partly conducted at the ACT node of the Australian National Fabrication Facility, and the ANU node of the Australian Microscopy and Microanalysis Facility. We thank S. Surve and S. Zhao for experimental assistance.

Author information

Authors and Affiliations

  1. School of Engineering, The Australian National University, Canberra, Australian Capital Territory, Australia

    Jun Peng, Daniel Walter, Yiliang Wu, The Duong, Heping Shen, Klaus J. Weber, Thomas P. White & Kylie R. Catchpole

  2. Centre for Advanced Microscopy, The Australian National University, Canberra, Australian Capital Territory, Australia

    Felipe Kremer & Frank Brink

  3. School of Physics & State Key Laboratory of Optoelectronic Materials and Technologies, Sun Yat-sen University, Guangzhou, China

    Yi Ji, Jin Xiang & Dingyong Zhong

  4. Research Center for New Energy Technology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai, China

    Wenzhu Liu

  5. Research School of Chemistry, The Australian National University, Canberra, Australian Capital Territory, Australia

    Teng Lu & Yun Liu

  6. Australian National Fabrication Facility, Research School of Physics, The Australian National University, Canberra, Australian Capital Territory, Australia

    Li Li & Olivier Lee Cheong Lem

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  1. Jun Peng
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Contributions

J.P. conceived the idea, designed the overall experiments and led the project. J.P. optimized the sputtered TiOxNy thin films. J.P. and Y.W. prepared and characterized the perovskite cell devices. F.K. and F.B. performed the TEM measurements and analysis. D.W., T.P.W. and K.J.W. conducted the device numerical simulation. Y.J. and J.X. performed the XPS/UPS measurements and analysis. D.Z. supervised the XPS/UPS measurements and analysis. Y.W. performed the Hall effect measurements and analysis. W.L. performed the EQE measurements. T.L. and Y.L. performed the atomic force microscopy measurements. T.D. and H.S. performed the steady-state and time-resolved photoluminescence, UV–Vis transmittance and absorption measurements. L.L. and O.L.C.L. conducted the SEM measurements. K.R.C. and T.P.W. supervised the project. J.P. wrote the manuscript. All authors contributed to the discussion of the results and revision of the manuscript.

Corresponding authors

Correspondence to Jun Peng, Thomas P. White or Kylie R. Catchpole.

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Competing interests

The Australian National University has filed a PCT patent (PCT/AU2021/051266) related to the subject matter of this manuscript.

Peer review information

Nature thanks Michael McGehee, Md. Shahiduzzaman and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data figures and tables

Extended Data Fig. 1 Surface morphology characterisation by AFM.

a, Bare FTO substrate. b, FTO/TiN substrate without post-annealing treatment (labeled as ‘As-deposited’). c, FTO/TiOxNy substrate annealed at 300oC (labeled as ‘300 C’). d, FTO/TiOxNy substrate annealed at 350oC (labeled as ‘350 C’). e, FTO/TiOxNy substrate annealed at 400oC (labeled as ‘400 C’). f, FTO/TiOxNy substrate annealed at 450oC (labeled as ‘450 C’). g, FTO/TiOxNy substrate annealed at 500oC (labeled as ‘500 C’). h, FTO/TiOxNy substrate annealed at 550oC (labeled as ‘550 C’). Note that the legend of ‘RMS’ represents root mean square of the surface roughness.

Extended Data Fig. 2 XPS element analysis.

The atomic ratio of O to Ti and N to Ti for TiOxNy thin films annealed at different temperatures.

Extended Data Fig. 3 TEM characterisation.

a, TiOxNy without annealing (‘As-deposited’). b, TiOxNy annealed at 300oC. c, TiOxNy annealed at 400oC. d, TiOxNy annealed at 500oC.

Extended Data Fig. 4 TEM characterisation and simulation of the diffraction pattern.

a and b, TiOxNy annealed at 350oC. c and d, TiOxNy annealed at 450oC. e and f, TiOxNy annealed at 550oC. Note that the non-continuous diffraction ring visible in Fig. 4f diffraction pattern is caused by the low crystal density within the specimen.

Extended Data Fig. 5 Optical bandgap characterisation.

Tauc plots for the as-deposited TiN film and TiOxNy films annealed at different temperatures. Note that all films (~50 nm) were deposited on quartz substrates.

Extended Data Fig. 6 Device structure.

a, The cross-sectional SEM image of the TiOxNy-based cell with a structure of glass/FTO/TiOxNy (~40 nm)/meso-TiO2 (~50 nm)/ultrathin PMMA:PCBM (<3nm)/Perovskite (~500 nm)/ultrathin PMMA (<3 nm)/P3HT:CuPc (~65 nm)/Gold. b, The cross-sectional SEM image of the TiOx-based cell with a structure of glass/FTO/TiOx (~50 nm)/meso-TiO2 (~50 nm)/ultrathin PMMA:PCBM (<3 nm)/Perovskite (~500 nm)/ultrathin PMMA (<3 nm)/P3HT:CuPc (~65 nm)/Gold. Note that the meso-TiO2 and perovskite represent mesoporous TiO2 and Cs0.05FA0.9MA0.05PbI2.74Br0.26, respectively.

Extended Data Fig. 7 Device characterisation.

a, VOC and JSC distribution for the TiOx-based cells (12 cells) and the TiOxNy-based cells (14 cells). b, The J-V curve of the perovskite cells based on the TiOxNy ETLs, which were annealed at 550oC. c, The J-V parameters distribution of the TiOxNy (annealed at 550oC) based cells (15 cells).

Extended Data Fig. 8 Effects of electron transport layers with different carrier densities on the performance of perovskite solar cells.

a, Simulated J-V curves where only ETL doping is varied using dopant densities taken from Hall effect measurements. b, Experimental J-V curves for the reference TiOx and TiOxNy PSCs. Reduction in FF and increase in Ohmic series resistance is predominantly due to electron depletion in the ETL layer. c, Energy level diagram of electron quasi-Fermi levels and conduction band, illustrating the resistive voltage loss in the ETL for the lowly-doped cases. Note that Energy levels and electron concentrations are calculated at 22.5 mA/cm2 for ETLs with doping densities equivalent to TiOx (5x1014 cm−3) and TiOxNy (3x1017 cm−3). d, Electron concentration in the ETL for doping levels from 5x1014 – 1018 cm−3. Note that the dash-dot horizontal lines mark the dopant defect concentration, indicating the magnitude of electron depletion. With the exception of extremely high doping at 1018 cm−3, in no case does the free electron concentration reach even the same order of magnitude as the fixed dopant concentration. e-f, Contour plots of perovskite solar cell fill factor (e) and open-circuit voltage (f) across a range of ETL doping levels and electron affinity. Note that the stars mark the conditions simulated in Fig. 9a. The vertical dashed lines mark the doping levels of the TiOx and optimized TiOxNy films fabricated in this work. Electron depletion from the ETL suggests that high doping is in general necessary to achieve fill factors on the order of 85% or above.

Extended Data Fig. 9 Device stability characterisation.

a, Light-soaking stability tests. b, Damp-heat stability tests. Note that SPO represents steady-state power output measured by maximum power point voltage (VMPP) tracking under continuous 1 sun illumination intensity. The device structure of the encapsulated cells is glass/FTO/TiOxNy (or TiOx)/m-TiO2/PMMA:PCBM/Perovskite/PMMA/P3HT:CuPc/MoOx (~10 nm)/IZO (~40 nm)/Au, where the perovskite is Cs0.05FA0.9MA0.05PbI2.74Br0.26. Details of encapsulation are provided in the experimental section.

Extended Data Table 1 Summarised parameters for the Hall-effect measurements
Full size table

Supplementary information

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This file contains model details, Figs. 1–6, Tables 1–5 and additional references.

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Peng, J., Kremer, F., Walter, D. et al. Centimetre-scale perovskite solar cells with fill factors of more than 86 per cent. Nature 601, 573–578 (2022). https://doi.org/10.1038/s41586-021-04216-5

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