Solar cell efficiency tables (version 12)

Consolidated tables showing an extensive listing of the highest independently confirmed efficiencies for solar cells and modules are presented. Guidelines for inclusion of results into these tables are outlined and new entries since January 1998 are briefly described. © 1998 John Wiley & Sons, Ltd.     

Silicon solar cells

The key attributes for achieving high-efficiency crystalline silicon solar cells are identified and historical developments leading to their realization discussed. Despite the achievement of laboratory cells with performance approaching the theoretical limit, commercial cell designs need to evolve significantly to realize their potential. In particular, the development of cell structures and processes that facilitate entirely activated device volumes in conjunction with well-passivated metal contacts a nd front and rear surfaces is essential (and yet not overly challenging) to achieve commercial devices of 20% efficiency from solar-grade substrates. The inevitable trend towards thinner substrates will force manufacturers to evolve their designs in this direction or else suffer substantial performance loss. Eventually, a thin-film technology will likely dominate, with thin-film crystalline silicon cells being a serious candidate. Present commercial techniques and processes are in general unsuitable for t hin-film fabrication, with even greater importance placed on the achievement of devices with entirely activated volumes (diffusion lengths much greater than device thicknesses), well-passivated metal contacts and surfaces and the important inclusion of li ght trapping. The recent achievement of 21.5% efficiency on a thin crystalline silicon cell (less than 50 μm thick) adds credibility to the pursuit of crystalline silicon in thin films, with a key attribute of this laboratory cell being its extremely good light trapping that nullifies the long-term criticism of crystalline silicon regarding its poor absorption properties and correspondingly perceived inability to achieve high-performance thin-film devices. For low-cost, low-quality polycrystalline sil icon material, the parallel-multijunction cell structure may provide a mechanism for achieving entirely activated cell volumes with the potential to achieve reasonable efficiencies at low cost over the next decade.     

On inner-outer factorization

The calculation of an inner-outer factorization of a proper, rational matrix by state-space methods is considered. Particular attention is given to the extraction of the inner factor, so that a minimal realization is obtained for this factor.     

The separate effects of E60Q in Lactobacillus casei thymidylate synthase delineate between mechanisms for formation of intermediates in catalysis

X-Ray crystal structures of Lactobacillus casei thymidylate synthase (TS) mutant complexes of E60D with dUMP, and E60Q with dUMP or FdUMP, as well as ternary complexes with folate analog inhibitor CB3717, are described. The structures we report address the decrease in rate of formation of ternary complexes in the E60 mutants. Structures of ternary complexes of L.casei TS mimic ligand-bound TS just prior to covalent bond formation between ligands and protein. Ternary complex structures of L.casei TS E60Q show the ligands are not optimally aligned for making the necessary covalent bonds. Since CB3717 is an analog of the open, activated form of the cofactor, these structures suggest that the slow rate of ternary complex formation in E60 mutants is at least partly the result of impaired alignment of ligands in the active site after binding and activation of the cofactor. Binary complexes of TS E60Q and TS E60D with substrate (dUMP) show no change in dUMP position or occupancy. These results are consistent with the fact that Kd(dUMP) and Km(dUMP) are almost the same, and the rates of folate-independent debromination of 5-bromo-dUMP are even higher than for wild type TS.      

Solar cell efficiency tables (version 5)

Updated tables showing an extensivé listing of the highest independently confirmed efficiencies for solar cells and modules are presented. Guidelines for inclusion of results into these tables are outlined and several new entries since July 1994 are briefly described.     

Shock Compression and Initiation of LX-10

LX-10 is a high energy density solid explosive consisting of 94.5% octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and 5.5% Viton A Binder pressed to 1.865 g/cm³ (98.4% of theoretical maximum density). In this paper the shock compression and initiation of chemical reaction in LX-10 by sustained shock pressures of 0.4 to 3 GPa are studied experimentally using embedded pressure and particle velocity gauges. The resulting pressure and particle velocity histories are evaluated theoretically using the ignition and growth reactive flow computer model of shock initiation and detonation. Manganin resistance and polyvinylidene fluoride (PVF₂) ferroelectric pressure gauges are both employed in the low pressure (0.4 – 0.7 GPa) shock compression experiments. Multiple manganin pressure and multiple electromagnetic foil particle velocity gauges measure the growth of reaction at various positions in LX-10 shocked to 1 – 3 GPa. The reactive flow modeling results imply that less than one percent of the LX-10 shocked to 0.4 – 0.7 GPa reacts in fifteen microseconds. For the higher pressure experiments, the ignition and growth model accurately calculates the pressure and/or particle velocity buildup in LX-10 as the reaction grows toward detonation. The LX-10 calculations are compared to those for the well-calibrated explosive PBX-9404, which contains 94% HMX and a reactive binder. Since it has the inert binder Viton A and better mechanical properties than PBX-9404, LX-10 is demonstrated to be significantly less reactive than PBX-9404 at these shock pressures. Therefore LX-10 is safer than PBX-9404 in many hazard and vulnerability scenarios to which solid explosives may be subjected.     

Decreased emitter sheet resistivity loss in high-eficiency silicon solar cells

State-of-the-art two-dimensional (2D) numerical semiconductor device simulation tools are applied to bifacially contacted silicon solar cells of practical dimensions in order to investigate the 2D effects arising from ohmic voltage drops in cell emitters due to finite front metal grid line spacings. the 2D simulations show that for typical front finger spacings of high-efficiency silicon solar cells the minority carrier flow in the base deviates strongly from the purely linear flow assumed by one-dimensional (1D) theory. Compared to conventional 1D theory, this 2D effect results in reduced emitter sheet resistivity losses, an increased optimum front finger spacing and a reduced impact of finger spacing on cell efficiency. the 2D effects are of particular importance for concentrator solar cells. The 2D simulations presented in this work considerably improve the general understanding of internal device physics of high-efficiency silicon solar cells and reveal the limits of 1D models for the simulation of these devices.     

World solar challenge 1993: The trans-australian solar car race

In November 1993, over 50 solar cars left Darwin for the tortuous 3000 kilometre journey south across Australia to Adelaide. the top cars set a pace difficult for conventional vehicles to maintain. the winner, the Honda Dream, averaged 85 kilometres per hour (53 mph), with all top five place getters shattering the previous race record set by the General Motors (GM) Sunraycer in 1987. the improved performance was due to better aerodynamics, motor and power train efficiency and improved output power from the photovoltaic arrays on these cars. This report describes the race with emphasis on the solar cell and module technology used by the leading cars.     

Accelerated publication 23.5% efficient silicon solar cell

The passivated emitter and rear locally diffused cell structure has been redesigned and has yielded independently confirmed one-sun eficiencies of up to 23.5%, the highest ever for a silicon cell. A dotted front emitter contact design, PBr₃ liquid-source phosphorus diffusions and 400-μm thick 10-cm diameter wafers have contributed to this improvement. Some of the new cells have demonstrated open-circuit voltages of 709 mV with an ‘inverted’ pyramid surface structure, the highest ever for a 23%-efficiency silicon cell. Further improvement is expected in the near future.     

Limiting efficiency for current‐constrained two‐terminal tandem cell stacks

Tandem stacks of solar cells have clearly shown their ability to increase the efficiency of solar energy conversion. In the past, the challenge in making these devices often has been in the materials science area, working around the constraints imposed by different materials to meet requirements imposed by lattice constant and bandgap. However, developments in the field of low‐dimensional structures; particularly superlattices, may allow generic approaches to developing tandem stacks of large numbers of cells. The current flowing through such devices will have to be constrained so that it is the same through all the cells within the stack since separately contacting such large numbers of cells is impractical. The series‐constrained two‐terminal tandem solar cell is compared with the unconstrained tandem solar cell for stacks containing both small and large numbers of cells. As expected, we find that the detailed balance limiting efficiencies for the two‐terminal cell are less than those for the unconstrained device involving the same number of cells, due to the constraint imposed by current matching. However the difference is always less than 1.5% relative under the design spectrum. However, the two‐terminal case shows much greater variation in efficiency if the spectrum varies from that for which the design was optimised. A relationship is derived between the performance of a two‐terminal stack of a finite number of cells and the performance of an unconstrained stack of an infinite number of cells. This shows that the performance of the two‐terminal device approaches that of the unconstrained device as the number of cells in the stack approaches infinity. Copyright © 2002 John Wiley & Sons, Ltd.