Hot electron effect in nanoscopically thin photovoltaic junctions

Abstract

The open circuit voltage in ultrathin amorphous silicon solar cells is found to increase with light energy ͑frequency͒, due to extraction of hot electrons. The ultrathin nature of these junctions also leads to large internal electric fields, yielding reduced recombination and increased current. A simple phenomenological argument provides a qualitative understanding of these effects and gives guidelines for designing future, high-efficiency, hot electron solar cells. A J sc [I-V] J sc [EQE] P/P(60 nm) J sc (mA/cm 2 ) D (nm) J sc Z h u , e t a l . A/A(60 nm) FIG. 3. ͑Color online͒ Variation of short circuit current density with total junction thickness. J sc vs D under AM1.5 illumination, as measured from I-Vs ͑squares͒, calculated by integrating EQE͑͒ ͑triangles͒, integrated optical absorbance A, normalized to the D = 60 nm value ͑circles͒, and normalized power density as modeled in Ref. 17 ͑dash͒.233121-2 Kempa et al. Appl. Phys. Lett. 95, 233121 ͑2009͒

Optical Absorption Characteristic in Thin a-Si Film Embedded Between an Ultrathin Metal Grating and a Metal Reflector

“…The ultrathin active layer of 30 nm of our absorber structure may seem too thin to form a p-i-n junction. However, an a-Si solar cell of a 20 nm thick p-i-n (5 nm-10 nm-5 nm) junction has been experimentally demonstrated and it has been reported that the ultrathin nature of these junctions can lead to large internal electric fields, yielding reduced recombination and increased current [24].…”

Photoelectric properties of GaAs p-n-junction under illumination of intense laser radiation

“…All this reduces conversion efficiency of solar cells. Recently it was shown [3] that the extraction of hot electrons increases the open circuit voltage in ultrathin α-Si p-i-n solar cells. To observe the increase of the open circuit voltage the thickness of the solar cells must be less than 25 nm.…”

Optical and electrical mappings of surface plasmon cavity modes

“…Recent theoretical work by Kempa shows that hot electrons generated in a semiconductor [52] can couple their excess free energy into an adjacent metal surface in the form of SPPs [53]. By comparing electron-phonon and electron-plasmon coupling probability amplitudes, he concluded that hot electrons are more probable to couple to surface plasmons.…”