This is an artist’s illustration of a 2D layered hybrid perovskite. Image: Los Alamos National Laboratory.In the eternal search for next-generation, high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory (LANL) and their partners have created innovative two-dimensional (2D) layered hybrid perovskites that allow greater freedom for designing and fabricating efficient optoelectronic devices. Industrial and consumer applications of these layered perovskites could include low cost solar cells, LEDs, laser diodes, detectors and other nano-optoelectronic devices.
"Our material is a layered compound, meaning it is a stack of 2D layers of perovskites with nanometer thickness (like a stack of sheets), and the 2D perovskite layers are separated by thin organic layers," explained Jean-Christophe Blancon from LANL, lead author of a paper on this work in Science. "This work could overturn conventional wisdom on the limitations of device designs based on layered perovskites."
The 2D, near-single-crystalline thin films have an out-of-plane orientation, allowing uninhibited charge transport to occur through the perovskite layers in planar devices. At the edges of the perovskite layers, the new research has now discovered "layer-edge-states". These are key to both the high conversion efficiency of the perovskite solar cells (>12%) and the high fluorescence efficiency (a few tens of percent) of the perovskite LEDs. The spontaneous conversion of excitons (bound electron-hole pairs) to free carriers via the layer-edge states appears to be key for improving these photovoltaic and light-emitting thin-film layered materials.
The team investigated both the photophysical and optoelectronic properties of phase-pure homogenous 2D perovskites. They were able to show that thin films have an intrinsic mechanism for dissociating the strongly-bound electron-hole pairs (excitons) to long-lived free-carriers provided by lower energy states at the edges of the layered perovskites.
Moreover, once the carriers are trapped at these edge states, they remain protected and do not lose their energy via non-radiative processes. This means they can contribute to photocurrent in a photovoltaic device or radiatively recombine efficiently for light-emission applications.
"These materials are quantum hybrid materials, possessing physical properties of both organic semiconductors and inorganic semiconducting quantum wells," said Jared Crochet of the Physical Chemistry and Applied Spectroscopy group at LANL. "We are just beginning to understand the interplay of the organic and inorganic components in 2D perovskites and this result underpins how unique properties can arise from competing physical properties."
"These results address a long-standing problem not just for the perovskite family, but relevant to a large group of materials where edges and surface states generally degrade the optoelectronic properties, which can now be chemically designed and engineered to achieve efficient flow of charge and energy leading to high-efficiency optoelectronic devices," said Aditya Mohite, who leads the perovskite program in the Material Synthesis and Integrated devices group at LANL.
"The 2D hybrid perovskites continue to surprise. When we first designed these materials we were hoping that high quality samples of them would exhibit novel optoelectronic properties," said co-author Mercouri Kanatzidis from Northwestern University. "Well, they have done so and then some. They have exceeded our expectations and are proving to be truly amazing systems. We have only scratched the surface of what is there – sorry for the pun – in this 2D family and we anticipate continued excitement going forward."
This story is adapted from material from Los Alamos National Laboratory, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.