![]() Quantum dots (QDs) have been employed in the practical implementation of such a concept. By introducing one additional energy level between conduction band (CB) and valence band (VB), photons with insufficient energy to pump electrons from VB to CB can use this intermediate band (IB) as a stepping stone to generate an electron-hole pair. Amongst these, QDSCs have the potential to achieve intermediate band solar cells with a theoretical conversion efficiency up to 63.2%. Hot carrier SCs, multi-junction SCs and quantum dot solar cells (QDSCs) aim to improve the efficiency by utilising the solar spectrum more effectively. Over the past decades, great efforts have been devoted to realising solar cells (SCs) that can exceed the Shockley–Queisser limit of 31%. IET Generation, Transmission & Distribution.IET Electrical Systems in Transportation.IET Cyber-Physical Systems: Theory & Applications.IET Collaborative Intelligent Manufacturing.CAAI Transactions on Intelligence Technology.We expect a conversion efficiency of up to 38.7% for 200-period QD-enhanced solar cells. Starting from an accepted value of 32.5% for no QD layers and using the measured 0.017mA/QD layer increase-see Figure 3(a)-Figure 4 shows the resulting efficiencies. Using detailed balance theory, we calculate the efficiency of a standard triple-junction cell as a function of the number of QD layers. ![]() Some voltage reduction is expected because of QD band-gap tuning, but this can be minimized with optimized strain balancing. This contributes to a reduction in open-circuit voltage. Addition of 40 QD layers raises the current density to 26.0mA/cm 2, which represents an ~8% increase. The baseline GaAs-cell performance exhibits typical values for this type of photovoltaic cell without antireflection coating (short-circuit current density J sc=24.1mA/cm 2, open-circuit voltage V oc=1046mV, and efficiency η=16.2%). External quantum-efficiency (EQE) and current density-voltage data shows additional current generation by multiple QD layers within a GaAs solar cell.įigure 3(b) shows illuminated current density-voltage curves for GaAs solar cells without QDs and with 10- and 40-period strain-balanced QD layers. Its size and density are intimately tied to the epitaxial growth conditions.įigure 3. The InAs/GaAs combination is the most extensively studied QD system. The QD density is ~5×10 10/cm 2 with nominal dimensions of 6×30nm 2 (height × base). Figure 2 shows an atomic-force-microscopy image of InAs QDs on a GaAs surface. A tensile-strain compensation layer is used to create strain-neutral layer stacks containing as many as 40 periods. ![]() For successive QD layers, compressive stress accumulates, ultimately leading to degraded QD uniformity and device properties. 4 InAs QDs are grown epitaxially based on the Stranski-Kranstanow mode, which relies on strain mismatch between the GaAs matrix and InAs to form the QDs. 3 We examined use of nanostructured indium arsenide (InAs) quantum dots (QDs) within GaAs solar cells to improve efficiency. Theoretical calculations indicate that the conversion efficiency can exceed 45%, either by extending the spectral bandwidth of the middle cell 2 or through implementation of an intermediate-band solar-cell concept. AM0: Airmass zero reference solar spectrum (outside the Earth's atmosphere). Epitaxial triple-junction cell and solar-spectrum splitting per junction. ![]()
0 Comments
Leave a Reply. |