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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, FA0.83Cs0.17Pb(I1‐xBrx)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 (VOC) 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 FA0.83Cs0.17Pb(I1‐xBrx)3 show that such VOC 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. [ABSTRACT FROM AUTHOR]

Two dimensional/three‐dimensional (2D/3D) metal halide perovskite heterostructures have attracted great interest in photovoltaic and light‐emitting diode (LEDs) applications. In both, their implementation results in an improvement in device efficiency yet the understanding of these heterostructures remains incomplete. In this work the role of organic cations, essential for the formation of 2D perovskite structures is unraveled, in a range of metal halide perovskite heterostructures. These heterostructures are used to fabricate efficient green perovskite LEDs and a strong dependence between cation content and device performance is shown. The crystal structure, charge‐carrier transport and dynamics, and the electronic structure of these heterostructures are studied and it is shown that the presence of crystalline 2D perovskite inhibits electron injection and ultimately lowers device performance. This work highlights the importance of optimizing the composition of these heterostructures in ensuring optimal device performance across all parameters and suggests that developing routes to inject charge‐carriers directly into 2D perovskite structures will be important in ensuring the continued development of perovskite LEDs based on these heterostructures. [ABSTRACT FROM AUTHOR]

Defect management in perovskite solar cells (PSCs) via surface passivation has become a cornerstone in maximizing both stability and solar-to-electrical power conversion efficiency (PCE) of devices by reducing defect densities and/or improving energetic alignment between the perovskite and charge-transporting layers. Despite this, few reports explore the use of roll-to-roll compatible technologies to deposit such interfacial treatments, limiting the applicability of passivation in real-world contexts. In this work, iso-butylammonium bromide (i-BABr) is spray-coated onto a Cs0.15FA0.85PbI2.85Cl0.15 perovskite surface which is deposited using gas-assisted ultrasonic spray coating. It is found that i-BABr treatments result in the formation of a quasi-2D perovskite layer. The spray-coated surface treatment results in an impressive 80 mV improvement in the median open-circuit voltage with respect to untreated devices. Importantly, the spray-coated passivation results in very similar positive benefits to the application of spin-coated treatments demonstrating the promise of the spray-passivation methodology. It is shown that devices created in this manner demonstrate PCEs of up to 21.0% (19.4% stabilized), representing the highest reported efficiency for one-step, spray-coated methylammonium-free PSCs. This work represents the first demonstration of a spray-coated surface passivation treatment that is compatible with high-throughput, roll-to-roll processing. [ABSTRACT FROM AUTHOR]

Understanding the kinetic competition between charge extraction and recombination, and how this is impacted by mobile ions, remains a key challenge in perovskite solar cells (PSCs). Here, this issue is addressed by combining operando photoluminescence (PL) measurements, which allow the measurement of real‐time PL spectra during current–voltage (J–V) scans under 1‐sun equivalent illumination, with the results of drift‐diffusion simulations. This operando PL analysis allows direct comparison between the internal performance (recombination currents and quasi‐Fermi‐level‐splitting (QFLS)) and the external performance (J–V) of a PSC during operation. Analyses of four PSCs with different electron transport materials (ETMs) quantify how a deeper ETM LUMO induces greater interfacial recombination, while a shallower LUMO impedes charge extraction. Furthermore, it is found that a low ETM mobility leads to charge accumulation in the perovskite under short‐circuit conditions. However, thisalone cannot explain the remarkably high short‐circuit QFLS of over 1 eV which is observed in all devices. Instead, drift‐diffusion simulations allow this effect to be assigned to the presence of mobile ions which screen the internal electric field at short‐circuit and lead to a reduction in the short‐circuit current density by over 2 mA cm−2 in the best device. [ABSTRACT FROM AUTHOR]

Mixed lead‐tin (Pb:Sn) halide perovskites are promising absorbers with narrow‐bandgaps (1.25–1.4 eV) suitable for high‐efficiency all‐perovskite tandem solar cells. However, solution processing of optimally thick Pb:Sn perovskite films is notoriously difficult in comparison with their neat‐Pb counterparts. This is partly due to the rapid crystallization of Sn‐based perovskites, resulting in films that have a high degree of roughness. Rougher films are harder to coat conformally with subsequent layers using solution‐based processing techniques leading to contact between the absorber and the top metal electrode in completed devices, resulting in a loss of VOC, fill factor, efficiency, and stability. Herein, this study employs a non‐continuous layer of alumina nanoparticles distributed on the surface of rough Pb:Sn perovskite films. Using this approach, the conformality of the subsequent electron‐transport layer, which is only tens of nanometres in thickness is improved. The overall maximum‐power‐point‐tracked efficiency improves by 65% and the steady‐state VOC improves by 28%. Application of the alumina nanoparticles as an interfacial buffer layer also results in highly reproducible Pb:Sn solar cell devices while simultaneously improving device stability at 65 °C under full spectrum simulated solar irradiance. Aged devices show a six‐fold improvement in stability over pristine Pb:Sn devices, increasing their lifetime to 120 h. [ABSTRACT FROM AUTHOR]

Mixed‐halide perovskites offer ideal bandgaps for tandem solar cells, but photoinduced halide segregation compromises photovoltaic device performance. This study explores the influence of a hole‐transport layer, necessary for a full device, by monitoring halide segregation through in situ, concurrent X‐ray diffraction and photoluminescence measurements to disentangle compositional and optoelectronic changes. This work demonstrates that top coating FA0.83Cs0.17Pb(Br0.4I0.6)3 perovskite films with a poly(triaryl)amine (PTAA) hole‐extraction layer surprisingly leads to suppression of halide segregation because photogenerated charge carriers are rapidly trapped at interfacial defects that do not drive halide segregation. However, the generation of iodide‐enriched regions near the perovskite/PTAA interface enhances hole back‐transfer from the PTAA layer through improved energy level offsets, increasing radiative recombination losses. It is further found that while passivation with a piperidinium salt slows halide segregation in perovskite films, the addition of a PTAA top‐coating accelerates such effects, elucidating the specific nature of trap types that are able to drive the halide segregation process. This work highlights the importance of selective passivation techniques for achieving efficient and stable wide‐bandgap perovskite photovoltaic devices. [ABSTRACT FROM AUTHOR]