Measuring just microns across, these tiny devices convert light into electrons, whose subsequent movement generates an electronic signal. Above a certain energy level, electrons can move freely. An electron moving into a lower energy state can transfer enough energy to knock loose another electron. The energy given off then catapults a second electron from the WSe2 into the MoSe2, where both electrons become free to move and generate electricity.
“Normally, when an electron jumps between energy states, it wastes energy. In our experiment, the waste energy instead creates another electron, doubling its efficiency. Understanding such processes, together with improved designs that push beyond the theoretical efficiency limits, will have a broad significance with regard to designing new ultra-efficient photovoltaic devices.”
“The electron in WSe2 that is initially energized by the photon has an energy that is low with respect to WSe2,” said Fatemeh Barati, a graduate student in Gabor’s Quantum Materials Optoelectronics lab and the co-first author of the research paper.
In the prototype the researchers developed, one photon can generate two electrons or more through a process called electron multiplication.