Photogeneration Quantum Yield and Character of Free Charges and Excitons in PbSe Nanorods
2020
Kulkarni, Aditya | Evers, Wiel H. | van Waas, Thomas P. | Siebbeles, Laurens D. A.
Lead selenide (PbSe) nanorods are of interest for applications in infrared LEDs, lasers, and photovoltaics due to the possibility of tuning their band gap from the far- to the near-infrared by decreasing their radius. We study the photogeneration quantum yield and properties of free charges and excitons in PbSe nanorods using a combination of time-resolved transient optical absorption and terahertz spectroscopy. Photoexcitation predominantly leads to the formation of excitons and to a smaller extent to free mobile charges. Theoretical analysis of the exprimental data yields an exciton polarizability of 10–³⁵ C m² V–¹. The sum of the mobilities of a free electron and a hole is found to be close to 100 cm² V–¹ s–¹. The high quantum yield of excitons makes PbSe nanorods of interest as a gain material in near-infrared LEDs or lasers. To use PbSe nanorods in photovoltaics, heterojunctions must be realized so that excitons can dissociate into free charges.
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