Unraveling quantum size-dependent optical phenomena in hot carrier quantum well structures

The enhancement of power conversion efficiency beyond the theoretical limit of single-junction solar cells is a key objective in the advancement of hot carrier solar cells. Recent findings indicate that quantum wells (QWs) can effectively generate hot carriers by confining charged carriers within their potential wells and by optimizing material properties. Here, we investigate the impact of quantum confinement on the thermodynamic properties of photogenerated hot carriers in p–i–n InGaAs/InAlAs heterostructure diodes, utilizing QW thicknesses of 4, 5.5, and 7.5 nm. The experimental findings indicate that the widest QW demonstrates more pronounced hot carrier effects than the thinner quantum wells. This observation aligns with theoretical predictions and underscores the significance of the well width in influencing carrier dynamics. Additionally, the open-circuit voltage of the samples demonstrates a correlation with the degree of quantum confinement, mirroring trends observed in the quasi-Fermi level splitting of hot carriers. However, the substantial photo-absorption occurring in the InAlAs barrier presents challenges in accurately distinguishing the photocurrent attributed to hot carrier populations in the QWs from that arising from thermalized carriers within the barrier. This study examines the impact of quantum confinement on the optical properties of non-equilibrium hot carriers in QW structures and offers insights for developing efficient hot carrier absorbers for photovoltaic applications.