Lance M. Wheeler

The overarching goal of the voucher project is to evaluate the suitability of NexTC materials as functional layers in perovskite photovoltaic technology. There are several different perovskite device configurations that are being pursued for commercialization. Most are superstrate configuration (light enters the device through the glass substrate) and can be subdivided into two categories: PIN and NIP. At minimum, PIN devices have a transparent conductor (typically Indium Tin Dioxide [ITO] or Fluorine-Doped Tin Oxide [FTO]) and hole transport layer (HTL) deposited on glass before the perovskite is deposited. Alternatively, NIP devices have a transparent conductor and electron transport layer (ETL) deposited before the perovskite is deposited. NexTC produces several inks that can be deposited to replace or modify the transparent conductor and/or the ETL or HTL, depending on the device. NLR will produce PIN and NIP perovskite devices on substrates that have been coated by NexTC and compare to NLR-standard devices that perform among the best for research labs across the world. The work will ultimately expose NexTC products to the up-and-coming perovskite PV industry.

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.

Persistent photoconductivity and optoelectronic synaptic behavior are demonstrated in solution‐processed mesoscopic α‐phase vanadium pentoxide (V ₂ O ₅ ) thin films. First‐principles simulations coupled with the two‐site Holstein polaron hopping model show that vacancies at the terminal oxygen position lead to long recombination times because photoexcited electrons and holes reside on different layers separated by the van der Waals gap, forming a weakly coupled interlayer exciton polaron. Mid‐gap polaronic states also significantly broaden the photoresponse of the films to span across visible and infrared wavelengths. By controlling the amplitude/intensity, duration, and/or number of optical pulses, tunable optoelectronic memory functions, such as short‐term and long‐term plasticity, are experimentally established in V ₂ O ₅ ‐based optoelectronic synapses. Device fabrication was extended to mechanically flexible ultrathin glass substrates. Flexible optoelectronic synapses maintained high performance after 150 bending cycles.

The high-temperature spin and electronic transitions in LaCoO₃ have recently been leveraged to create neuromorphic (brain-inspired) devices. While these devices have shown the potential for impactful functionality in next-generation computing systems, the nanoscale dynamics of the spin and electronic transitions that underlie their operation are not well understood. Inhomogeneities related to interfaces, electrode contacts, strain, and crystal defects can all affect device performance, making nanoscale characterization of the transitions essential for producing consistent and reliable devices. Here, we demonstrate the first nanoscale in situ measurement of the spin transition in LaCoO₃ at device-relevant temperatures (25-325 °C) over length scales of tens of nanometers using STEM-EELS. This measurement is enabled by an Al₂O₃ coating, which prevents unwanted reduction of the LaCoO₃ specimen at high temperature and vacuum. The detailed understanding of LaCoO₃ transition dynamics enabled by such measurements will be crucial for optimizing LaCoO₃-based neuromorphic devices and increasing reliability for real-world application.

Despite the extraordinary rise in power conversion efficiency over the last decade, metal halide perovskite (MHP) photovoltaics remain more mechanically fragile than other PV technologies. In this work, the scribe area, created by the monolithic interconnection of thin‐film solar cells, is used to extrinsically reinforce the mechanical robustness of packaged MHP solar modules. In contrast to the epoxy‐based chemistries often leveraged in the MHP literature, silane‐grafted polyolefin encapsulants are designed to form strong covalent bonds to oxide surfaces, specifically to glass and the transparent conductive oxide at the base of the scribe line. Pseudo‐modules encapsulated with silane‐grafted polyolefin are measured with more than an order‐of‐magnitude enhancement infracture energy from 0.27 ± 0.01 J·m ⁻² (no scribes) to 5.97 ± 0.42 J·m ⁻² (scribes perpendicular to delamination directioncovering ≈2.2% of the module area). The silane‐grafted polyolefin retains strong adhesion even after undergoing an accelerated IEC 61215 thermal cycling test consisting of 250 cycles. We find that the in‐scribe bonding allows perovskite modules to have adhesion strength comparable to commercial c‐Si and CdTe technologies with only 5% reduction in the active module area. This manufacturing‐compatible approach offers a practical solution to address the mechanical integrity challenges in MHP solar modules, regardless of cell architecture.

The work combines NREL as the world leader in perovskite and polymeric materials, and teams them up with The Dow Chemical Company, the world leader in commercial production of PV encapsulation materials. The team will design and evaluate encapsulation materials that are tailored to perovskite photovoltaics. Demonstration of polyolefin-based encapsulants for perovskite PV will be impactful for a number of reasons: 1) There is no clear-cut choice for encapsulation for perovskite PV to date. 2) There is high synthetic control of the material properties for future perovskite module designs. 3) Among the candidate materials, they have the highest barrier properties, 4) Polyolefins are the most prevalent (>20 million metric tons consumed in the US alone) and inexpensive (<1.5 $USD/kg) polymers used worldwide. 5) They are recyclable and may play a role in future of circular PV materials. 6) They are manufactured domestically. The work also highlights careful design of perovskite transport layer materials for surviving vacuum encapsulation.

Though power conversion is an important metric for photovoltaic windows, it must be balanced with visible transmittance, aesthetics (color and haze), and thermal performance. Optical properties are often reported, but thermal performance is typically neglected entirely in photovoltaic window design. Here, we introduce the strategy of using laminate layers to improve the thermo-optical performance of perovskite-based photovoltaic insulating glass units. We design the laminates and insulating glass units by coupling a transfer matrix method optical model to a 1D heat transfer model. We validate our models with experimental fabrication of one-dimensional photonic crystal layers that are deposited on glass and laminated to the perovskite photovoltaic device. The holistic designs neutralize the inherent transmissive red color, and the "red low-e" design dramatically reduce emissivity of the glass surface to significantly improve thermal insulation and boost the photocurrent of the device.

Current photovoltaic (PV) panels typically contain interconnected solar cells that are vacuum laminated with a polymer encapsulant between two pieces of glass or glass with a polymer backsheet. This packaging approach is ubiquitous in conventional photovoltaic technologies such as silicon and thin-film solar modules, contributing to thermal management, mechanical reinforcement, and environmental protection to enable the long lifetimes necessary to become financially acceptable. Commercial vacuum lamination processes typically occur at 150 °C to ensure cross-linking and/or glass bonding of the encapsulant to the glass and PV cells. Perovskite solar cells (PSCs) have emerged as a promising next-generation PV technology that is known to degrade under thermal stresses, especially at temperatures above 100 °C. In this study, we determine degradation modes during lamination and engineer internal diffusion barriers within the PSC to withstand the harsh thermal conditions of vacuum lamination. PSCs with self-assembled monolayers at the ITO interface and SnO _X layers deposited by atomic layer deposition at the electron extraction side of the device endured vacuum lamination at conditions typical of commercial PV processes (150 °C) without degradation. This work demonstrates that perovskite PV can be integrated into the existing module lamination process, enabling future single- and multijunction modules utilizing perovskite absorbers.