Kelly Schutt

Nickel oxide (NiO _x ) is a common hole transport layer (HTL) in perovskite photovoltaics, but the chemical reactivity of NiOx surfaces accelerates degradation when contacting perovskites. We developed an ultrathin, conformal tin oxide (SnO _x ) interlayer to suppress interfacial reactivity between NiO _x and perovskite. SnO _x is typically an electron transport layer, but we show that the energy alignment can be modified for hole extraction using molecules with dipoles. This synergy yielded high efficiency in perovskite photovoltaic devices and showed an ~10x improvement in T 90 lifetime in open-circuit conditions under AM1.5G at 65°C. This structure also improves resilience to thermomechanical durability, as minimodules retained 95.7% of their initial performance after 1000 thermal cycles (−65° to 85°C), highlighting the importance of interfaces for robust perovskite photovoltaic modules.

Current encapsulation architectures for thin‐film metal halide perovskite do not adequately eliminate all ambient stressors. Here, we develop low transmission rate barrier layers using atomic layer deposited (ALD) aluminum oxide grown directly on the completed photovoltaic (PV) device stack to provide an additional seal, prior to full packaging. We investigate the effect of deposition temperature and oxidant chemistries on the barrier growth for protection of perovskite photovoltaic devices. We characterize the layers individually, then integrate into devices to detail the tradeoff between protection and deposition compatibility. To enhance compatibility and impermeability, we present an approach using water as the aluminum oxidant during nucleation and switching from water to ozone for the remainder of the growth. At 50 nm, the barrier results in a water vapor transmission rate (WVTR) of 4.5·10 ⁻⁴ g/m ² /day, and 1,000‐hour device stability under 45°C with 85% relative humidity without further packaging. This barrier provides sufficient protection to enable minimal degradation of the perovskite solar cells while completely submerged in water for 140 minutes. Additionally, we characterize the oxygen transmission rate (OTR) to be 0.49 cm ³ /m ² /day at 23°C and 0% relative humidity, which is 1.5 orders of magnitude improvement over the OTR of the current encapsulation.

A new electrochemical metric quantifies detrimental redox activity in nickel oxide hole transport layers, directly linking surface reactivity to solar cell efficiency and guiding targeted passivation for stable, high-performance photovoltaics.

We highlight opportunities for a transformative shift in perovskite solar cell design by expanding electron transport layers (ETLs) beyond fullerenes. Fullerenes have known limitations, including constraints on open-circuit voltage, stability, and mechanical integrity. Recently, fullerene-free p-i-n cells with power conversion efficiencies exceeding 25% have been demonstrated via both naphthalene diimide-SnO _x bilayers and nonfullerene acceptor-based ETLs. Despite successes, fullerenes remain the de facto ETLs for perovskites. Drawing lessons from organic photovoltaics, where it took decades to transition from fullerenes to more broadly available and efficient materials, we explore pathways to accelerate the development and adoption of fullerene-free ETLs. This requires understanding the similarities and differences between organic and perovskite solar cells, which will necessitate carefully designing fullerene replacements with both, high efficiency and also, critically, durability under operation. Here, we incorporate literature data to facilitate comparisons, and independently conduct fracture energy measurements for alternative ETL configurations to motivate their adoption.

Here, a thorough study of the effects of multiple stressors on a series of FAMACsPb(IBr)3 solar cells was assessed to test the stability of such systems for space applications. Combinations of thermal cycling, constant illumination, and electric field during the temperature ramp were all investigated. In all cases, some degradation of the solar cells was apparent, which was nearly reversible in the case of protocol 1 (thermal) and protocol 2 (thermal with illumination). However, under protocols 3 and 4 (thermal, illumination, and variable electric field), the devices did not return to initial conditions, suggesting possible irreversible degradation. An evaluation of device parameters: short circuit current density (Jsc), fill factor (FF), and open circuit voltage (Voc) shows that the Jsc is the least affected parameter [T = 450 K, remaining factors Jsc(T)/Jsc(300 K) ≥ 94%] regardless of protocol. For all protocols, the remaining factors at T = 450 K were 85%–90% and 78%–85% for FF and Voc, respectively. Under protocol 4 (practical solar cell operation), the FF and Voc behavior lags behind that of protocols 1 and 2 until T > 420 K. Overall, the results indicate that metal halide perovskite solar cells have potential for space power applications, as the device’s remaining factors were ≥90% for protocols 4, 2, and 1 for T ≤ 380, 400, and 420 K, respectively. With regard to CubeSat missions testing metal halide perovskites by applying a controlled voltage (V = 0.001 V) between measurements (protocol 2), particularly when the device is idle, degradation from combined stressors can be mitigated, reducing the risk of irreversible damage.

Robust contact schemes that boost stability and simplify the production process are needed for perovskite solar cells (PSCs). We codeposited perovskite and hole-selective contact while protecting the perovskite to enable deposition of SnO _x /Ag without the use of a fullerene. The SnO _x , prepared through atomic layer deposition, serves as a durable inorganic electron transport layer. Tailoring the oxygen vacancy defects in the SnO _x layer led to power conversion efficiencies (PCEs) of >25%. Our devices exhibit superior stability over conventional p-i-n PSCs, successfully meeting several benchmark stability tests. They retained >95% PCE after 2000 hours of continuous operation at their maximum power point under simulated AM1.5 illumination at 65°C. Additionally, they boast a certified T ₉₇ lifetime exceeding 1000 hours.

Heterojunctions are used to tailor the properties of semiconductors in optoelectronic devices, yet for emerging devices composed of metal halide perovskites, fabricating perovskite/perovskite heterojunctions has proved challenging due to solvent incompatibilities and rapid homogenization due to ion migration. Recent studies have demonstrated various strategies for using perovskite nanocrystals as a component to fabricate perovskite/perovskite heterojunctions, either with a perovskite thin film or a second nanocrystal layer. Heterojunctions such as these can impart many advantages of both bulk and nanocrystalline perovskite morphologies. This perspective focuses on recent developments of solution‐processed perovskite heterojunctions for solar cells and novel optoelectronic devices, in particular, highlighting the demonstrated and potential advantages of nanocrystal‐enabled fabrication strategies. A central tenet of this perspective is that the synthesis and dispersion of perovskite nanocrystals in non‐polar organic solvents offers a key processing advantage over traditional perovskite precursor solutions in polar solvents since the former allows for layer‐by‐layer deposition without dissolving an underlying perovskite film or crystal. This processing advantage, coupled with nanocrystal size control and ligand chemistry, enables perovskite heterojunctions with highly tunable optical and electrical properties. Such heterojunctions may enable disruptive technological advances in broad classes of devices such as solar cells, photodetectors, sensors, and (in)coherent photon sources with tunable polarization.

Perovskite solar cells have achieved the highest power conversion efficiencies on metal oxide n‐type layers, including SnO₂ and TiO₂. Despite ZnO having superior optoelectronic properties to these metal oxides, such as improved transmittance, higher conductivity, and closer conduction band alignment to methylammonium (MA)PbI₃, ZnO is largely overlooked due to a chemical instability when in contact with metal halide perovskites, which leads to rapid decomposition of the perovskite. While surface passivation techniques have somewhat mitigated this instability, investigations as to whether all metal halide perovskites exhibit this instability with ZnO are yet to be undertaken. Experimental methods to elucidate the degradation mechanisms at ZnO–MAPbI₃ interfaces are developed. By substituting MA with formamidinium (FA) and cesium (Cs), the stability of the perovskite–ZnO interface is greatly enhanced and it is found that stability compares favorably with SnO₂‐based devices after high‐intensity UV irradiation and 85 °C thermal stressing. For devices comprising FA‐ and Cs‐based metal halide perovskite absorber layers on ZnO, a 21.1% scanned power conversion efficiency and 18% steady‐state power output are achieved. This work demonstrates that ZnO appears to be as feasible an n‐type charge extraction layer as SnO₂, with many foreseeable advantages, provided that MA cations are avoided.

State‐of‐the‐art perovskite‐based solar cells employ expensive, organic hole transporting materials (HTMs) such as Spiro‐OMeTAD that, in turn, limits the commercialization of this promising technology. Herein an HTM (EDOT‐Amide‐TPA) is reported in which a functional amide‐based backbone is introduced, which allows this material to be synthesized in a simple condensation reaction with an estimated cost of <$5 g⁻¹. When employed in perovskite solar cells, EDOT‐Amide‐TPA demonstrates stabilized power conversion efficiencies up to 20.0% and reproducibly outperforms Spiro‐OMeTAD in direct comparisons. Time resolved microwave conductivity measurements indicate that the observed improvement originates from a faster hole injection rate from the perovskite to EDOT‐Amide‐TPA. Additionally, the devices exhibit an improved lifetime, which is assigned to the coordination of the amide bond to the Li‐additive, offering a novel strategy to hamper the migration of additives. It is shown that, despite the lack of a conjugated backbone, the amide‐based HTM can outperform state‐of‐the‐art HTMs at a fraction of the cost, thereby providing a novel set of design strategies to develop new, low‐cost HTMs.

Crystal-PAINT super-resolution imaging enables high-throughput metrology of DNA nanostructures for quantitative analysis of arrays formed through self-assembly.