Self-assembling monolayers in mixed tin-lead perovskite solar cells

Isabella Taupitz^a, Sebastian Berwig^a, Yeonghun Yun^a, Maxim Simmonds^a, Alexandra Miaskiewicz^a, Philipp Tockhorn^a, Steve Albrecht^a

^aHelmholtz-Zentrum Berlin für Materialien, Hahn-Meitner-Platz, 1, Berlin, Germany

Materials for Sustainable Development Conference (MATSUS)
Proceedings of MATSUS Spring 2024 Conference (MATSUS24)

#PerTanCell - Perovskite Tandem Solar Cells

Barcelona, Spain, 2024 March 4th - 8th

Organizers: Kai Brinkmann and Felix Lang

Poster, Isabella Taupitz, 549
Publication date: 18th December 2023

Tandem solar cells are able to exceed the maximum efficiency (detailed balance limit) of single junction
devices by far. In all-perovskite tandem solar cells, two perovskite absorbers with different bandgaps
(narrow-bandgap, NBG with Eg<1.3 eV and wide-bandgap, WBG with Eg>1.5 eV) are paired for optimal
utilization of the solar spectrum whilst profiting from the excellent optoelectronic properties of
perovskite films. Recently, all-perovskite tandem solar cells have reached 28% certified power-
conversion efficiency and are quickly approaching that of silicon-perovskite tandem solar cells [1]. Yet,
losses at the interface between tin/lead NBG subcell and hole transport layer (HTL) still limit the
performance of all-perovskite tandem solar cells. Very recently a few approaches have been published
demonstrating a successful replacement of the standard HTL PEDOT:PSS, which is known for its
detrimental influence on device performance, by self-assembling monolayer (SAM) materials [2–6].
Nevertheless, the details of charge-carrier dynamics and other film characteristics such as
crystallization of SAM-based mixed Sn/Pb perovskite films still lack understanding.
In this work, we study the influence of the pseudo-halide additive lead-thiocyanate (Pb(SCN)2) on the
performance of PEDOT:PSS- and SAM-based mixed Sn/Pb perovskite devices. Additive engineering
with thiocyanate compounds has been a major research focus for NBG perovskites and led the way to
the current record efficiencies in single-junction NBG and all-perovskite solar cells. However, our study
shows that a perovskite composition which has been developed for PEDOT:PSS fails solar cell behavior
upon replacing PEDOT:PSS with SAM (PCE > 16 % vs. PCE < 2 %). Results from JV measurements, as
well as transient surface photovoltage (trSPV) and transient photoluminescence (trPL) measurements
suggest that charge carrier extraction is blocked in SAM-based, Pb(SCN)2-containing devices.
Remarkably, morphology analysis and absolute PL measurements show significantly enlarged grain
size, smooth surface morphology and increased quasi Fermi-level splitting (QFLS) of Pb(SCN)2
containing films when fabricated on SAM, compared to films without Pb(SCN)2 (~0.75 eV vs. ~0.85 eV).
In contrast, for films fabricated on PEDOT:PSS there are only minor differences. These findings point
out, that a mixed Sn/Pb NBG perovskite composition which has been developed for high performance
PEDOT:PSS-based devices and all-perovskite tandems might not show the same device characteristics
when brought in contact with other HTMs instead. In conclusion, our study demonstrates that a careful
re-assessment of additive engineering plays a crucial role when replacing the standard hole-transport
material PEDOT:PSS in NBG sub-cells of all-perovskite tandem solar cells

References:

[1] Lin, R.; Wang, Y.; Lu, Q.; Tang, B.; Li, J.; Gao, H.; Gao, Y.; Li, H.; Ding, C.; Wen, J.; Wu, P.; Liu, C.; Zhao, S.; Xiao, K.; Liu, Z.; Ma, C.; Deng, Y.; Li, L.; Fan, F.; Tan, H. All- Perovskite Tandem Solar Cells with 3D/3D Bilayer Perovskite Heterojunction. Nature 2023, 620 (7976), 994–1000.

[2] Liu, C.; Lin, R.; Wang, Y.; Gao, H.; Wu, P.; Luo, H.; Zheng, X.; Tang, B.; Huang, Z.; Sun, H.; Zhao, S.; Guo, Y.; Wen, J.; Fan, F.; Tan, H. Efficient All‐Perovskite Tandem Solar Cells with Low‐Optical‐Loss Carbazolyl Interconnecting Layers. Angew. Chem. Int. Ed. 2023, e202313374.

[3] Pitaro, M.; Alonso, J. S.; Mario, L. D.; Romero, D. G.; Tran, K.; Zaharia, T.; Johansson, M. B.; Johansson, E. M. J.; Loi, M. A. A Carbazole-Based Self-Assembled Monolayer as the Hole Transport Layer for Efficient and Stable Cs0.25FA0.75Sn0.5Pb0.5I3 Solar Cells. J. Mater. Chem. A 2023, 11 (22), 11755–11766.

[4] Kapil, G.; Bessho, T.; Sanehira, Y.; Sahamir, S. R.; Chen, M.; Baranwal, A. K.; Liu, D.; Sono, Y.; Hirotani, D.; Nomura, D.; Nishimura, K.; Kamarudin, M. A.; Shen, Q.; Segawa, H.; Hayase, S. Tin–Lead Perovskite Solar Cells Fabricated on Hole Selective Monolayers. ACS Energy Lett. 2022, 7 (3), 966–974.

[5] Datta, K.; Wang, J.; Zhang, D.; Zardetto, V.; Remmerswaal, W. H. M.; Weijtens, C. H. L.; Wienk, M. M.; Janssen, R. A. J. Monolithic All-Perovskite Tandem Solar Cells with Minimized Optical and Energetic Losses. Adv. Mater. 2022, 34 (11), 2110053.

[6] Leijtens, T.; Prasanna, R.; Bush, K. A.; Eperon, G. E.; Raiford, J. A.; Gold-Parker, A.; Wolf, E. J.; Swifter, S. A.; Boyd, C. C.; Wang, H.-P.; Toney, M. F.; Bent, S. F.; McGehee, M. D. Tin–Lead Halide Perovskites with Improved Thermal and Air Stability for Efficient All-Perovskite Tandem Solar Cells. Sustain. Energy Fuels 2018, 2 (11), 2450–2459.

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