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The performance of tandem stacks of Group III–V multijunction solar cells continues to improve rapidly, both through improved performance of the individual cells in the stack and through increase in the number of stacked cells. As the radiative efficiency of these individual cells increases, radiative coupling between the stacked cells becomes an increasingly important factor not only in cell design, but also in accurate efficiency measurement and in determining performance of cells and systems under varying spectral conditions in the field. Past modeling has concentrated on electroluminescent coupling between the cells, although photoluminescent coupling is shown to be important for cells operating near their maximum power point voltage or below or when junction defect recombination is significant. Extension of earlier models is proposed to allow this non-negligible component of luminescent coupling to be included. The refined model is validated by measurement of the closely related external emission from both single and double junction cells. [ABSTRACT FROM AUTHOR]

The performance of dual-junction solar cells with a Si bottom cell has been investigated both theoretically and experimentally. Simulations show that adding a top junction with an energy bandgap of 1.6 -1.9 eV to a standard silicon solar cell enables efficiencies over 38%. Currently, top junctions of GaInP (1.8 eV) are the most promising as they can achieve 1-sun efficiencies of 20.8% [1]. We fabricated mechanically stacked, four terminal GaInP/Si tandem solar cells using a transparent adhesive between the subcells. These tandem devices achieved an efficiency of 27% under AM1.5 g spectral conditions. Higher efficiencies can be achieved by using an improved Si-bottom cell and by optimizing the dual-junction device for long-wavelength light and luminescent coupling between the two junctions. [ABSTRACT FROM AUTHOR]

Ultrathin solar cells reduce material usage and allow the use of lower-quality materials thanks to their one order of magnitude smaller thickness than their conventional counterparts. However, efficient photonic light-trapping is required to harvest the incident light efficiently for an otherwise insufficient absorber thickness. Quasi-random photonic crystals are predicted to have high efficient light-trapping while being more robust under angle and thickness variations than simple photonic crystals. Here we experimentally demonstrate a light-trapping solution based on quasi-random photonic crystals fabricated by polymer blend lithography. We control the average lattice parameter by modifying the spin-coating speed. We demonstrate an ultrathin GaAs cell of 260 nm with a rear quasi-random pattern with submicron features, and a J sc = 26.4 mA/cm 2 and an efficiency of 22.35% under the global solar spectrum. [Display omitted] • Low-cost fabrication of quasi-random photonic crystals using polymer blends. • Facile tuning of the structure's reciprocal space by changing the spin speed. • Ultrathin GaAs cell of 260 nm absorber with a best in class efficiency of 22.35%. • High Voc (1.12 V) GaAs ultrathin cells with and without rear-pattern. [ABSTRACT FROM AUTHOR]

Traditional metallic contacts on solar cells can cover a substantial portion of the device area, resulting in shadowing of light that diminishes the amount of current collected. In this paper, we developed trapezoidal electron-beam evaporated Ti/Al front grid fingers on GaAs single-junction solar cells to decrease the optical shadowing and increase the photogenerated current. We observe a high fill factor of 87% at 1-Sun light intensity and we observe no degradation on the open-circuit voltage. The short-circuit current density is found to increase by 0.4 mA/cm2 when compared to previously demonstrated electroplated Ni/Au front grid fingers, resulting in an efficiency improvement of ~0.8% absolute. • Developed front grid fingers with trapezoidal cross section • Contacts fabrication by conventional semiconductor tools • Devices exhibited increased photocurrent and efficiency improvement by 0.8% absolute [ABSTRACT FROM AUTHOR]