Diffusion Length Of Photogenerated Carriers Research Articles

Ultrafast carrier dynamics in GeSn thin film based on time-resolved terahertz spectroscopy

We measure the time-resolved terahertz spectroscopy of GeSn thin film and studied the ultrafast dynamics of its photo-generated carriers. The experimental results show that there are photo-generated carriers in GeSn under femtosecond laser excitation at 2500 nm, and its pump-induced photoconductivity can be explained by the Drude–Smith model. The carrier recombination process is mainly dominated by defect-assisted Auger processes and defect capture. The first- and second-order recombination rates are obtained by the rate equation fitting, which are (2.6 ± 1.1) × 10−2 ps−1 and (6.6 ± 1.8) × 10−19 cm3⋅ps−1, respectively. Meanwhile, we also obtain the diffusion length of photo-generated carriers in GeSn, which is about 0.4 μm, and it changes with the pump delay time. These results are important for the GeSn-based infrared optoelectronic devices, and demonstrate that GeSn materials can be applied to high-speed optoelectronic detectors and other applications.

High Efficiency Perovskite Solar Cells: Materials and Devices Engineering

Since the first report on 9.7% efficient solid-state perovskite solar cell (PSC) in 2012, perovskite photovoltaics received tremendous attentions. Efforts to increase power conversion efficiency (PCE) have been continuously made. As a result, a record PCE of 25.2% was certified in 2019, which surpassed those achieved from the conventional solar cells based on CIGS and CdTe. The superb photovoltaic performance of PSC is related to the defect-tolerant property, the long carrier lifetime, the long diffusion length of photo-generated carriers, and the high absorption coefficient. In this review, materials and devices engineering are described for achieving stability and higher PCE in PSCs. From the practical point of view, key technologies for materials, coating, and device fabrication are described, which is expected to be helpful to achieve high efficiency PSCs. Moreover, interfacial engineering methodologies toward hysteresis-less and stable PSCs are also presented to give insight into better understanding ion migration and recombination in PSCs.

Communication—Improving Optoelectronic Properties of Electrochemically Deposited Cuprous Oxide Thin-Films by Low-Temperature Post-Deposition Annealing

The effect of low-temperature post-deposition annealing (PDA) on electrochemically deposited cuprous oxide (ECD-Cu2O) thin-films was investigated. The PDA at 150°C drastically improved optoelectronic properties of ECD-Cu2O films regardless of annealing atmosphere. The films exhibits free exciton luminescence at room temperature and a high hole mobility about 18 cm2/V·s. Moreover, the diffusion length of photo-generated carriers increased around two times compared to the as-deposited film. On the other hands, the PDA at 200°C significantly deteriorated the optoelectronic properties presumably due to the increase of mid-gap defects in the Cu2O films.

Imaging the Long Transport Lengths of Photo-generated Carriers in Oriented Perovskite Films.

Organometal halide perovskite has emerged as a promising material for solar cells and optoelectronics. Although the long diffusion length of photogenerated carriers is believed to be a critical factor responsible for the material's high efficiency in solar cells, a direct study of carrier transport over long distances in organometal halide perovskites is still lacking. We fabricated highly oriented crystalline CH3NH3PbI3 (MAPbI3) thin-film lateral transport devices with long channel length (∼120 μm). By performing spatially scanned photocurrent imaging measurements with local illumination, we directly show that the perovskite films prepared here have very long transport lengths for photogenerated carriers, with a minority carrier (electron) diffusion length on the order of 10 μm. Our approach of applying scanning photocurrent microscopy to organometal halide perovskites may be further used to elucidate the carrier transport processes and the vastly different carrier diffusion lengths (∼100 nm to 100 μm) in different types of organometal halide perovskites.