The question the scientists had to respond to was, therefore: how do excited electrons in perovskites alter the shape of the crystal lattice?Looking inside nanocrystalsTo take a peek inside a perovskite (formamidinium lead bromide) synthesized at Empa by Maryna Bodnarchuk and ETH professor Maksym Kovalenko, the scientists utilized an ultrafast electron diffraction beamline facility at the Stanford National Accelerator Laboratory (SLAC) that produces very short pulses of electrons lasting only a hundred femtoseconds, or millionths of a millionth of a second.These electrons then struck the perovskite nanocrystals, about 10 nanometres in size, and the diffracted electrons are gathered on a screen. Even small modifications in the crystal structure can be measured in this way.The ETH scientists made use of an unique feature of the SLAC beamline to take photos of the crystal structure throughout and after the absorption of a photon: by using the very same laser to create the photons and to activate the electron pulse, they were able to control the photons arrival time at the nanocrystals relative to that of the electrons by altering the distance that the photons had to take a trip. Instead, they observed a shift towards increased symmetry– the excited electrons had actually slightly corrected the alignment of out the skewed crystal structure of the perovskite.From design calculations, they were able to deduce that several excitons– bound pairs of excited electrons and positively charged holes left behind by their excitation– might work together in correcting the alignment of out the lattice.
The question the scientists had to answer was, therefore: how do ecstatic electrons in perovskites change the shape of the crystal lattice?Looking inside nanocrystalsTo take a peek inside a perovskite (formamidinium lead bromide) synthesized at Empa by Maryna Bodnarchuk and ETH professor Maksym Kovalenko, the researchers used an ultrafast electron diffraction beamline facility at the Stanford National Accelerator Laboratory (SLAC) that produces really brief pulses of electrons lasting just a hundred femtoseconds, or millionths of a millionth of a second.These electrons then struck the perovskite nanocrystals, about 10 nanometres in size, and the diffracted electrons are gathered on a screen. Even small modifications in the crystal structure can be determined in this way.The ETH researchers made use of an unique function of the SLAC beamline to take pictures of the crystal structure throughout and after the absorption of a photon: by using the exact same laser to produce the photons and to set off the electron pulse, they were able to control the photons arrival time at the nanocrystals relative to that of the electrons by changing the distance that the photons had to travel. Instead, they observed a shift towards increased balance– the thrilled electrons had somewhat straightened out the manipulated crystal structure of the perovskite.From model calculations, they were able to deduce that numerous excitons– bound sets of excited electrons and positively charged holes left behind by their excitation– might comply in correcting out the lattice.
