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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%.

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

Abstract:

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_0.83Cs_0.17Pb(I_1-xBr_x)₃ 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_OC) 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_0.83Cs_0.17Pb(I_1-xBr_x)₃ show that such V_OC 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.