MRS Meetings and Events

 

EN06.06.08 2023 MRS Fall Meeting

Band-Like Transport and Charge Carrier Dynamics in BiOI Films

When and Where

Nov 29, 2023
10:45am - 11:00am

Hynes, Level 3, Room 306

Presenter

Co-Author(s)

Snigdha Lal1,Marcello Righetto1,Aleksander Ulatowski1,Silvia Motti1,2,Zhuotong Sun3,Judith Driscoll3,Robert Hoye1,Laura Herz1

University of Oxford1,University of Southampton2,University of Cambridge3

Abstract

Snigdha Lal1,Marcello Righetto1,Aleksander Ulatowski1,Silvia Motti1,2,Zhuotong Sun3,Judith Driscoll3,Robert Hoye1,Laura Herz1

University of Oxford1,University of Southampton2,University of Cambridge3
Following the emergence of lead halide perovskites (LHPs) as materials for efficient solar cells, research has progressed to explore stable, abundant and non-toxic alternatives. However, the performance of such lead-free perovskite-inspired materials (PIMs) still lags significantly behind that of their LHP counterparts. For bismuth-based PIMs, one significant reason is a frequently observed ultrafast charge-carrier localization (or self-trapping), which imposes a fundamental limit on long-range mobility. BiOI is a widely studied 2D layered material which has recently been explored as a Pb-free PIM for photovoltaic applications. A wide bandgap material, it is highly suitable for tandem applications. However, despite reported defect tolerance and strong band-edge absorption, the power conversion efficiencies for BiOI-based devices has remained stunted with record efficiencies reaching barely 2%. An extensive photophysical study is needed to elucidate the performance limiting factors for BiOI along with highlighting the true intrinsic potential of the material as a photovoltaic absorber.<br/>Here, we report the charge-carrier dynamics of BiOI and show that unlike many other Bi-based compositions such as Cs<sub>2</sub>AgBiBr<sub>6</sub> and Ag-Bi iodides, BiOI shows sustained band-like transport with respectable mobilities. Crucially our investigation reveals an absence of self-trapping despite the presence of strong electron phonon coupling and lower dimensionality. Using optical pump terahertz probe (OPTP) spectroscopy, time resolved microwave conductivity (TRMC) spectroscopy and time resolved photoluminescence (TRPL) spectroscopy, we unravel the early and long-time charge-carrier dynamics in BiOI and show that the material performance is limited by the presence of multi-phonon emission mediated non-radiative channels in the material. Using temperature-dependent OPTP transient, we quantify the bimolecular recombination constant and show that the material has low rates of band-to-band recombination likely originating from an indirect bandgap. Taken together with a slightly higher-lying direct bandgap, such low levels of intrinsic band-to-band recombination set high upper limits of achievable charge-carrier lifetime. Altogether, this contribution highlights the promise of BiOI solar cells.

Keywords

optical properties | photoconductivity

Symposium Organizers

Aron Huckaba, University of Kentucky
Cecilia Mattevi, Imperial College London
Elisa Riedo, New York University
Christopher Sutton, University of South Carolina

Publishing Alliance

MRS publishes with Springer Nature