Quantum confinement-tunable solar cell based on ultrathin amorphous germanium. (October 2020)

• Record Type: Journal Article
• Authors: Meddeb, Hosni; Osterthun, Norbert; Götz, Maximilian; Sergeev, Oleg; Gehrke, Kai; Vehse, Martin; Agert, Carsten
• Is Part Of: Nano energy. Volume 76(2020)
• Publication Date: 2020-10
• Subjects: Quantum confinement -- Quantum well -- Amorphous germanium nanostructure -- Optical resonant planar nanocavity -- Ultrathin film solar cell; Nanoscience -- Periodicals; Nanotechnology -- Periodicals; Nanostructured materials -- Periodicals; Power resources -- Technological innovations -- Periodicals; Nanoscience; Nanostructured materials; Nanotechnology; Power resources -- Technological innovations; Periodicals; 621.042
• DOI: 10.1016/j.nanoen.2020.105048
• Languages: English
• ISSNs: 2211-2855

Abstract

Abstract: Nanoscale semiconductors involve distinct fundamental phenomena and novel properties emerge due to dimensional restriction of the charge carriers' motion, known as quantum confinement (QC). In this study, the first investigation of quantum size effects in single quantum well (QW) solar cells based on ultrathin hydrogenated amorphous germanium (a-Ge:H) nanoabsorber is reported, using cost-effective, industrial-compatible and low-temperature production processes. The confinement in the growth direction due to the thickness reduction of the a-Ge:H absorber layer from 20 nm down below 2 nm, results in tunable optoelectronic properties and photovoltaics (PV) characteristics, while maintaining a comparable power conversion level. A major gain by a factor of two in open circuit-voltage is demonstrated, exceeding 700 mV with reducing the a-Ge:H QW thickness by an order of magnitude. Furthermore, the band gap widening yields a considerable enhancement of the fill factor from 45 to 65% due to the reduction of the conduction band offset at a-Ge:H (QW)/a-Si:H (barrier) heterojunction interface. The successful demonstration of a-Ge:H QW cells indicates the promising potential for multiple QWs implementation as nanoabsorber material in solar cells. Graphical abstract: Required dimensions (3.5 cm *9 cm). Image 1 Highlights: Ultrathin solar cell based on a-Ge:H nanoabsorber from 20 nm down below 2 nm. Quantum-size dependence of a-Ge:H QW bandgap widening by a CB upward shift. QC-tunable absorption threshold and PV characteristics in a-Ge:H QW solar cell. Enhancement of Voc above 700 mV and FF up to 65% due to QW thickness reduction.