A thin-film perovskite LED currently wastes four out of every five photons it produces, trapping them inside the device instead of letting them out as light. This collaboration between Cambridge and the Netherlands’ AMOLF institute tackles a fundamental optical bottleneck in two types of thin-film devices. For perovskite LEDs, light outcoupling is stuck at roughly 20% — most generated light never escapes. For solar cells, the team aims to push beyond the single-junction efficiency limit by using singlet fission, a process where one high-energy photon is split into two lower-energy photons that a silicon cell can then absorb. The core challenge is designing photonic structures that channel this infrared light toward the solar cell without introducing optical losses. If the photonic designs succeed, perovskite LEDs could approach near-100% forward-direction outcoupling, dramatically improving their efficiency for displays and lighting. The singlet-fission photon multiplier could boost the power output of silicon solar panels without changing the silicon cell itself. Neither application will reach consumers tomorrow — this is fundamental science in optical engineering and materials physics — but similar work on light management has already transformed how solar cells and LEDs are designed worldwide.
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This Centre-to-Centre collaboration addresses a set of research opportunities that require the close integration of optoelectronic materials and device engineering with state-of-the-art light management for large area solar cells and LEDs. The collaboration brings the AMOLF LMPV group, recognised for its work in 'light management' for solar cells, to work closely with the Cambridge research programme on thin-film perovskite and organic solar cells and LEDs. The AMOLF activity is centred in the very strong 'national laboratory' framework of solar cell research in the Netherlands, and brings strengths that have not been systematically developed in the UK. Thin-film diodes made with lead halide perovskites now support solar cells and LEDs with excellent electronic properties, but challenges with light in/outcoupling can limit performance. This is a particular challenge for perovskite LEDs for which light outcoupling is currently limited to 20%. By harnessing the special luminescent properties of perovskites, including photon recycling, with engineered optical structures, the outcoupling in the forward direction will be raised towards 100%. One way to improve a solar cell beyond the single-junction limit is to harvest the high-energy part of the solar spectrum with an organic material capable of singlet fission, a process by which the energy from one high-energy photon is shared between two lower-energy triplet exciton states. Cambridge has pioneered the science of singlet fission and developed the concept of the Photon Multiplier. In this all-optical thin-film device, incident high-energy photons (<540nm) will be converted into two low-energy photons, each at around 1000 nm, which can then be absorbed by a silicon solar cell underneath. The challenge to be undertaken here is to develop suitable photonic designs that direct the emission of these IR photons towards the Si solar cell without introducing optical losses in the module.
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