NREL

A few months ago, researchers from the University of Alabama, Jackson State University and NREL reported high-performance perovskite solar cells (PSCs) fabricated using rapid photonic annealing (RPA) based on ultraviolet light-emitting diode (UV-LED) sources. 

The schematic of thermal annealing (TA) and rapid photon annealing (RPA) annealing of SnO₂ ETL and perovskite absorber. Image from: Small

This approach replaces conventional thermal annealing with a fast, energy-efficient, and layer-specific process that enables precise control of film crystallization within seconds. The resulting PSCs achieved a power conversion efficiency of 23.03% - the highest reported for optically annealed perovskite devices.

Perovskite solar cells (PSCs) tend to degrade rapidly under reverse bias, a condition that arises during partial shading. At voltages below −2 V, current forced backward through shaded cells produces localized hotspots and thermal runaway, leading to catastrophic breakdown. Unlike silicon solar cells, where bypass diodes mitigate reverse bias, PSCs remain highly vulnerable due to structural weaknesses in their active layers, making it essential to pinpoint the mechanisms driving this failure.

Image credit: Joule

A recent study, led by the McGehee group at the University of Colorado Boulder in collaboration with the National Renewable Energy Laboratory (NREL), identifies nanoscale to microscale defects - particularly pinholes in the perovskite film - as the principal trigger of breakdown events. These defects are introduced during the solution-processing fabrication method, which is prone to creating gaps and thin spots due to film inhomogeneity. Although such pinholes have only a minor impact on overall power conversion efficiency, they represent weak points where localized heating and failure originate under stress conditions.

Perovskite solar cells (PSCs) are reaching impressive power conversion efficiencies, but long-term durability remains a major barrier to real-world impact. In a recent Perspective article, NREL researchers highlight why current stress tests (light, heat, humidity, etc.) are insufficient: they don’t accurately predict how PSCs will perform under field conditions. 

A more realistic path forward is a durability learning cycle, where lab and field testing continuously inform each other. The NREL team is recommending investigating the durability of perovskite solar modules - starting by placing them outside.

Halide perovskite solar cells with mixed-cation compositions often face instabilities under continuous illumination due to the deprotonation of methylammonium (CH₃NH₃⁺, MA⁺) cations. To address this issue, researchers from Tsinghua University, National Renewable Energy Laboratory (NREL) and Princeton University have evaluated the partial and complete deuteration of MA⁺ cations. 

This approach inhibits deprotonation and degradation, reduces the formation energy of the perovskite phase, improves grain growth, passivates defects, and restrains ion migration. As a result, perovskite solar cells incorporating this deuteration strategy achieved exceptional performance, including a high fill factor (FF) of 82.6% and a power conversion efficiency (PCE) of 25.6%.

A collaborative effort between NREL and CubicPV has yielded a perovskite minimodule with 24.0% certified efficiency, marking the first time a U.S. effort has set a record in the perovskite minimodule category.

Image credit: NREL

The researchers at NREL and at CubicPV made the minimodule consisting of multiple interconnected cells, with several steps in the fabrication sequence done at each location.

Increasing module efficiency and expanding manufacturing capacity play complementary roles in reducing costs of metal halide perovskite/silicon tandem solar modules, according to researchers at the U.S. Department of Energy's National Renewable Energy Laboratory (NREL). Each cost lever can play a similar role depending on a manufacturer’s ability to scale up and improve module performance.

They explain that tandem PV technology, created by pairing silicon with metal halide perovskites (MHPs) for example, can help create a solar module that can convert more sunlight to electricity than using silicon alone. This tandem technology is still in the early stages, and there are multiple options being pursued to integrate MHPs and silicon, with a lot of unknowns in terms of cost and performance. To address this gap, the researchers built a manufacturing cost model that combines laboratory processes with existing equipment and supply chains to compare different possible approaches at scale.

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 common in conventional photovoltaic technologies such as silicon and thin-film solar modules, contributing to thermal management, mechanical reinforcement, and environmental protection to enable long lifetimes. 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) are known to degrade under thermal stresses, especially at temperatures above 100 °C.

Researchers from NREL and The Dow Chemical Company have examined degradation modes during lamination and developed internal diffusion barriers within the PSC to withstand the harsh thermal conditions of vacuum lamination. 

Researchers at the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) and the Center for Hybrid Organic Inorganic Semiconductors for Energy (CHOISE), an Energy Frontier Research Center (EFRC), University of Wisconsin-Madison, University of Colorado Boulder, Duke University and University of Utah have discovered a new process to induce chirality in halide perovskite semiconductors, which could open the door to cutting-edge electronic applications.

The development is the latest in a series of advancements made by the team involving the introduction and control of chirality. Chirality refers to a structure that cannot be superimposed on its mirror image, such as a hand, and allows greater control of electrons by directing their “spin.” Most traditional optoelectronic devices in use today exploit control of charge and light but not the spin of the electron.

Researchers from City University of Hong Kong, National Renewable Energy Laboratory (NREL) and Imperial College London have improved the long-term stability of perovskite solar cells with an atomic-layer deposition (ALD) method that replaces the fullerene electron transport layer with tin oxide. 

Professor Zhu Zonglong (left) and Dr Gao Danpeng of City University of Hong Kong hold their innovative solar cells. Image credit: Eurekalert

The team started by depositing the perovskite and the hole-transporter layer in a single step. Then, they used ALD to create an oxygen-deficient tin oxide layer to reduce the band offset to a thicker, overgrown layer of normal tin oxide. Solar cells had a power conversion efficiency of more than 25%, and they retained more than 95% of efficiency after 2000 hours of maximum power point operations at 65°C. 

The U.S. Department of Energy (DOE) Solar Energy Technologies Office (SETO) Small Innovative Projects in Solar (SIPS) 2024 funding program provides $5.4 million for seedling R&D projects that focus on innovative and novel ideas in photovoltaics (PV) and concentrating solar-thermal power (CSP) and are riskier than research ideas based on established technologies.

The 16 selected projects were recently announced, among them were 5 perovskite-related projects.