Researchers from Penn State and Princeton University have made strides in creating a diode laser based on a perovskite material that can be deposited from solution on a laboratory benchtop.
Organic diode lasers, that are extremely hard to make, are sought after since they have many advantages. First, because organic semiconductors are relatively soft and flexible, organic lasers could be incorporated into new form factors not possible for their inorganic counterparts. While inorganic semiconductor lasers are relatively limited in the wavelengths, or colors, of light they emit, an organic laser can produce any wavelength a chemist cares to synthesize in the lab by tailoring the structure of the organic molecules. This tunability could be very useful in applications ranging from medical diagnostics to environmental sensing.
The key to succeeding in making such lasers may involve organic/inorganic perovskites; The material that the team is studying is composed of an inorganic perovskite sublattice with relatively big organic molecules confined in the middle. "The ultimate goal is to make an electrically driven perovskite laser diode," said the researchers. "That would be a game changer. It is fairly easy to make the perovskite material lase by optical pumping, that is, by shining another laser on it. However, this has only worked for very short pulses due to a poorly understood phenomenon we call lasing death. Getting it to go continuously is a key step toward an eventual electrically driven device. What we found in this recent study is a curious quirk. We can avoid lasing death entirely just by lowering the temperature of the material a little bit to induce a partial phase transition."
The team explained that "when we lowered the temperature below the phase transition, we were surprised to find that the material initially emitted light from the low temperature phase, but then changed over within 100 nanoseconds and began lasing from the high-temperature phase -- for over an hour," said the study's lead author. "It turned out that as the material heated up, although most of the material remained in the low-temperature phase, small pockets of the high-temperature phase formed, and that was where the lasing was coming from."
In some inorganic lasers there are narrow regions called quantum wells where charge carriers can be trapped as the electrons and holes fall into the wells. The intensity of the lasing depends on how many charge carriers can be packed into the quantum wells. In the perovskite material, the arrangement of the high-temperature-phase inclusions inside the low temperature bulk seems to mimic these quantum wells and may play a role in enabling the continuous lasing.
These results seem to point toward an opportunity to engineer a material that has the built-in qualities of this mixed phase arrangement, but without having to actually cool the material to low temperature. The current paper points to a couple of ideas for how those materials could be designed. The next big step then is to switch from optical pumping with an external laser to a perovskite laser diode that can be powered directly with electrical current.
"If we can solve the electrical pumping problem, perovskite lasers could turn into a technology with real commercial value," the team said.