|Title:||Analysis of one-sun monocrystalline rear-contacted silicon solar cells with efficiencies of 22.1%|
|Authors :||Dicker, Jochen|
|Published in :||Journal of Applied Physics|
|Publisher / Ed. Institution :||American Institute of Physics|
|License (according to publishing contract) :||Licence according to publishing contract|
|Type of review:||Peer review (publication)|
|Subjects :||Carrier lifetime; Semiconductor device models; Surface recombination; Silicon solar cells|
|Subject (DDC) :||621.3: Electrical engineering and electronics|
|Abstract:||21.4% efficient rear-contacted cells (RCC) with interdigitated contact grids processed at Fraunhofer ISE on 1.25 Ωcm float-zone silicon are analyzed in detail. The comprehensive description does not only include a two dimensional numerical device simulation, but also a detailed analysis of the optical carrier generation using optical ray tracing and a determination of the losses due to distributed metal resistance and perimeter currents employing a circuit simulation. Bulk- and surface recombination losses are separated combining carrier lifetime and open-circuit voltage measurements with numerical device simulation. The interface surface recombination velocity of the thermally oxidized emitter covering the front surface is deduced to be 1500 cm/s, the bulk diffusion length within the 1.25 Ωcm FZ silicon base is 1200 µm. Despite this excellent bulk diffusion length, the simulations reveal that at maximum power point 80% of the total recombination is due to Shockley Read Hall recombination in the base. A shunt effect at the floating emitter junction at the front side is shown to cause a strongly reduced spectral response for low illumination levels as well as a hump in the dark IV curve. Both effects could be modeled quantitatively assuming the same shunt resistance. Losses due to the distributed metal resistance within the contact grid (including non-generation losses) were determined to cause a fill factor decrease of 1% absolute. Loss currents flowing out of the cell perimeter leads to an additional fill factor loss of 1.5% absolute. The efficiency of the RCC structure was predicted to improve by 3% relative when changing the surface concentration of the front and rear emitter diffusion from 5x10^18 cm^-3 to 1x10^18 cm^-3 with the sheet resistance kept constant. In fact, this modification has lead to an increase in the realized cell efficiency from 21.4% to 22.1%, that is a 3.3% relative improvement.|
|Departement:||School of Engineering|
|Organisational Unit:||Institute of Computational Physics (ICP)|
|Publication type:||Article in scientific journal|
|Appears in Collections:||Publikationen School of Engineering|
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