Speaker
Description
Nanowires have been studied extensively in the last decades because they promise substantial improvements in several technologies. Ordered arrays of nanowires can generate similar photocurrent densities as thin-film solar cells by using only a fraction of the material. Due to their high aspect ratio nanowires are very surface sensitive, which can be challenging for (opto-)electronics. For photovoltaics specifically, it is important that the nanowires are covered by an insulating oxide to prevent short-circuits. Ideally, the insulating oxide is also passivating the nanowire surface but often this is not the case. Furthermore, fixed charges in the oxide can alter the electrostatic potential of the nanowires. It is agreed upon that a passivated surface with long charge carrier lifetimes is desirable, but the methods used to characterise nanowires cover the time-range in several orders of magnitude. Characterisation methods that investigate longer time-ranges seem to be preferred by researchers as they result in longer and apparently better lifetimes. Here, we compare a set of differently doped InP nanowires before and after they are coated by two different oxides. We study the photoluminescence of those nanowires by use of a streak-camera that can resolve ps lifetimes, and with time-correlated single photon counting that can resolve ns lifetimes. Then, by measuring the steady-state photoluminescence we calculate the quantum yield and scale the time-resolved photoluminescence decay. Depending on the doping and passivation, up to 4 separate decays can be distinguished. Furthermore, we show that during continuous illumination the intensity of emitted light varies in a time range of 30 min. We discuss the implications of independent photoluminescence decays at different time-ranges and their relevance for photovoltaics. This knowledge will help to understand the role of surface passivation in nanowire solar cells in order to obtain higher efficiencies.
| Speaker Country | Sweden |
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