No abstract

The influence of the point spacing and size on the cell efficiency is studied for different silicon solar cell structures with local rear contacts: the PERC (passivated emitter and rear cell) with its high recombination at the rear contacts and the LBSF (local back surface field) or PERL (passivated emitter and rear locally diffused) cell with reduced combination at the rear contacts due to a diffused high‐low junction (or LBSF) beneath the contacts. Float zone materials of different resistivities have been investigated. The experimental results are explained by three‐dimensional finite difference simulations for the open‐circuit voltage, the short‐circuit current and the fill factor.

A systematic experimental study is presented that aims at the optimization of the emitter of high-efficiency Si-solar cells. The emitter is processed by a homogeneous weak n' diffusion and an additional local deep n++ diffusion under the front grid. Solar cells and dark saturation current test structures with different homogeneous emitter sheet resistivitys variing between 40 Qlsq. and 300 Qlsq. and with different junction depths have been processed. In addition the junction depth and the sheet resistivity of the local n++ emitter was varied for each set of homogeneous emitter. As a further variation the phosphorous deep diffusion of the local emitter was either performed together with the deep diffusion of the homogeneous n' emitter or with an additional step before the n+-doping.The test structures and solar cells were analyzed by various techniques (doping profile, dark saturation current, photoconductance decay, solar cell parameters).With the optimized parameters for our solar cells efficiencies up to 22.3 % (AM1 5) have been achieved on FZ-silicon and 21.3 % on Cz-silicon. The Cz-Si result is, to our knowledge, a record value.

No abstract

Design and efficiency measurements of a mechanically stacked concentrator tandem solar cell are presented. The GaAs cell was grown by the LPE etch-back-regrowth method and has a diameter of 4 mm. The silicon solar cell is a high efficient LBSF concentrator solar cell of 5 mm diameter. Special care was taken to optimize the antireflection coatings on the back and front side of the GaAs solar cell. Both cells were processed at FhG-ISE in Freiburg. Their short circuit currents were measured at the ISE calibration laboratory under AM1.5d conditions. The efficiency measurements were performed at UPM-IES in Madrid under outdoor conditions. At 27 suns (AM1.5d, 25°C) the GaAs cell showed an efficiency of 22.9% and the silicon cell an efficiency of 2.9%. The two single cell efficiencies add to a tandem efficiency of 25.8% for the four terminal operation