Bandgap-universal passivation enables stable perovskite solar cells with low photovoltage loss.

Science (New York, N.Y.) 384:6697 (2024) 767-775

Authors:

Yen-Hung Lin, Vikram, Fengning Yang, Xue-Li Cao, Akash Dasgupta, Robert DJ Oliver, Aleksander M Ulatowski, Melissa M McCarthy, Xinyi Shen, Qimu Yuan, M Greyson Christoforo, Fion Sze Yan Yeung, Michael B Johnston, Nakita K Noel, Laura M Herz, M Saiful Islam, Henry J Snaith

Abstract:

The efficiency and longevity of metal-halide perovskite solar cells are typically dictated by nonradiative defect-mediated charge recombination. In this work, we demonstrate a vapor-based amino-silane passivation that reduces photovoltage deficits to around 100 millivolts (>90% of the thermodynamic limit) in perovskite solar cells of bandgaps between 1.6 and 1.8 electron volts, which is crucial for tandem applications. A primary-, secondary-, or tertiary-amino-silane alone negatively or barely affected perovskite crystallinity and charge transport, but amino-silanes that incorporate primary and secondary amines yield up to a 60-fold increase in photoluminescence quantum yield and preserve long-range conduction. Amino-silane-treated devices retained 95% power conversion efficiency for more than 1500 hours under full-spectrum sunlight at 85°C and open-circuit conditions in ambient air with a relative humidity of 50 to 60%.

Unraveling Loss Mechanisms Arising from Energy‐Level Misalignment between Metal Halide Perovskites and Hole Transport Layers

Advanced Functional Materials Wiley (2024)

Authors:

Jae Eun Lee, Silvia G Motti, Robert DJ Oliver, Siyu Yan, Henry J Snaith, Michael B Johnston, Laura M Herz

Abstract:

<jats:title>Abstract</jats:title><jats:p>Metal halide perovskites are promising light absorbers for multijunction photovoltaic applications because of their remarkable bandgap tunability, achieved through compositional mixing on the halide site. However, poor energy‐level alignment at the interface between wide‐bandgap mixed‐halide perovskites and charge‐extraction layers still causes significant losses in solar‐cell performance. Here, the origin of such losses is investigated, focusing on the energy‐level misalignment between the valence band maximum and the highest occupied molecular orbital (HOMO) for a commonly employed combination, FA<jats:sub>0.83</jats:sub>Cs<jats:sub>0.17</jats:sub>Pb(I<jats:sub>1‐x</jats:sub>Br<jats:sub>x</jats:sub>)<jats:sub>3</jats:sub> with bromide content x ranging from 0 to 1, and poly[bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine] (PTAA). A combination of time‐resolved photoluminescence spectroscopy and numerical modeling of charge‐carrier dynamics reveals that open‐circuit voltage (V<jats:sub>OC</jats:sub>) losses associated with a rising energy‐level misalignment derive from increasing accumulation of holes in the HOMO of PTAA, which then subsequently recombine non‐radiatively across the interface via interfacial defects. Simulations assuming an ideal choice of hole‐transport material to pair with FA<jats:sub>0.83</jats:sub>Cs<jats:sub>0.17</jats:sub>Pb(I<jats:sub>1‐x</jats:sub>Br<jats:sub>x</jats:sub>)<jats:sub>3</jats:sub> show that such V<jats:sub>OC</jats:sub> losses originating from energy‐level misalignment can be reduced by up to 70 mV. These findings highlight the urgent need for tailored charge‐extraction materials exhibiting improved energy‐level alignment with wide‐bandgap mixed‐halide perovskites to enable solar cells with improved power conversion efficiencies.</jats:p>

Direct and integrating sampling in terahertz receivers from wafer-scalable InAs nanowires

Nature Communications Springer Nature 15:1 (2024) 103

Authors:

Kun Peng, Nicholas Paul Morgan, Ford M Wagner, Thomas Siday, Chelsea Qiushi Xia, Didem Dede, Victor Boureau, Valerio Piazza, Anna Fontcuberta i Morral, Michael B Johnston

Abstract:

Terahertz (THz) radiation will play a pivotal role in wireless communications, sensing, spectroscopy and imaging technologies in the decades to come. THz emitters and receivers should thus be simplified in their design and miniaturized to become a commodity. In this work we demonstrate scalable photoconductive THz receivers based on horizontally-grown InAs nanowires (NWs) embedded in a bow-tie antenna that work at room temperature. The NWs provide a short photoconductivity lifetime while conserving high electron mobility. The large surface-to-volume ratio also ensures low dark current and thus low thermal noise, compared to narrow-bandgap bulk devices. By engineering the NW morphology, the NWs exhibit greatly different photoconductivity lifetimes, enabling the receivers to detect THz photons via both direct and integrating sampling modes. The broadband NW receivers are compatible with gating lasers across the entire range of telecom wavelengths (1.2–1.6 μm) and thus are ideal for inexpensive all-optical fibre-based THz time-domain spectroscopy and imaging systems. The devices are deterministically positioned by lithography and thus scalable to the wafer scale, opening the path for a new generation of commercial THz receivers.

Strong coupling in molecular systems: a simple predictor employing routine optical measurements

Nanophotonics (2024)

Authors:

MS Rider, EC Johnson, D Bates, WP Wardley, RH Gordon, RDJ Oliver, SP Armes, GJ Leggett, WL Barnes

Abstract:

We provide a simple method that enables readily acquired experimental data to be used to predict whether or not a candidate molecular material may exhibit strong coupling. Specifically, we explore the relationship between the hybrid molecular/photonic (polaritonic) states and the bulk optical response of the molecular material. For a given material, this approach enables a prediction of the maximum extent of strong coupling (vacuum Rabi splitting), irrespective of the nature of the confined light field. We provide formulae for the upper limit of the splitting in terms of the molar absorption coefficient, the attenuation coefficient, the extinction coefficient (imaginary part of the refractive index) and the absorbance. To illustrate this approach, we provide a number of examples, and we also discuss some of the limitations of our approach.

The Role of the Organic Cation in Developing Efficient Green Perovskite LEDs Based on Quasi‐2D Perovskite Heterostructures

Advanced Functional Materials Wiley (2023)

Authors:

Alexandra J Ramadan, Woo Hyeon Jeong, Robert DJ Oliver, Junke Jiang, Akash Dasgupta, Zhongcheng Yuan, Joel Smith, Jae Eun Lee, Silvia G Motti, Olivia Gough, Zhenlong Li, Laura M Herz, Michael B Johnston, Hyosung Choi, Jacky Even, Claudine Katan, Bo Ram Lee, Henry J Snaith