Photovoltaic & Optoelectronic Device Group

Abstract:

Trap‐related charge‐carrier recombination fundamentally limits the performance of perovskite solar cells and other optoelectronic devices. While improved fabrication and passivation techniques have reduced trap densities, the properties of trap states and their impact on the charge‐carrier dynamics in metal‐halide perovskites are still under debate. Here, a unified model is presented of the radiative and nonradiative recombination channels in a mixed formamidinium‐cesium lead iodide perovskite, including charge‐carrier trapping, de‐trapping and accumulation, as well as higher‐order recombination mechanisms. A fast initial photoluminescence (PL) decay component observed after pulsed photogeneration is demonstrated to result from rapid localization of free charge carriers in unoccupied trap states, which may be followed by de‐trapping, or nonradiative recombination with free carriers of opposite charge. Such initial decay components are shown to be highly sensitive to remnant charge carriers that accumulate in traps under pulsed‐laser excitation, with partial trap occupation masking the trap density actually present in the material. Finally, such modelling reveals a change in trap density at the phase transition, and disentangles the radiative and nonradiative charge recombination channels present in FA0.95Cs0.05PbI3, accurately predicting the experimentally recorded PL efficiencies between 50 and 295 K, and demonstrating that bimolecular recombination is a fully radiative process.

Abstract:

AbstractCoherent light sources in silicon photonics are the long‐sought Holy Grail because silicon‐based materials have indirect bandgap. Traditional strategies for realizing such sources, e.g., heterogeneous photonic integration, strain engineering, and nonlinear process, are technologically demanding. Here, a hybrid lasing device composed of perovskite nanocrystals and silicon nitride nanobeam cavity is demonstrated. SiN photonic crystal naonobeam cavities are fabricated on a solid substrate with significantly improved thermal and mechanical stabilities compared to conventional suspended ones. In addition, adding a poly (methyl methacrylate) (PMMA)‐encapsulation layer on top of the SiN can significantly boost the Q‐factor of the cavity mode. By dispersing perovskite nanocrystals as emitters in the PMMA layer, high‐performance coherent emissions are obtained in terms of lasing threshold, linewidth, and mode volumes. The work offers a compelling way of creating solution‐processed active integrated photonic devices based on the mature platform of silicon photonics for applications in optical information science and photonic quantum technology.