Wolfgang Jooss

Back contact buried contact solar cells with metallization wrap around electrodes

The authors present results on back contact buried contact solar cells based on the metallization wrap around (MWA) concept. In this cell design, the current is conducted over metallized edges of the solar cell to the rear side busbar. The applied processing sequence is almost identical to the one of conventional buried contact cells and is based on p/n-contact isolation by mechanical abrasion. One major problem of MWA solar cells seems to be the long current paths in the fingers to the collecting busbar on the rear side. Therefore device simulations were carried out in order to find the optimum grid design for different cell sizes (10/spl times/10 cm/sup 2/ and 12.5/spl times/12.5 cm/sup 2/). The device simulations showed that the MWA solar cell concept leads to higher efficiencies as compared to conventional cells. Best efficiencies obtained in this study are /spl eta/=17.5% (cell area 25 cm/sup 2/) and /spl eta/=16.6% (100 cm/sup 2/) on Cz-Si. For mc-Si efficiencies of /spl eta/=15.7% (25 cm/sup 2/) and /spl eta/=14.4% (100 cm/sup 2/) were reached.

Large area multicrystalline silicon buried contact solar cells with bulk passivation and an efficiency of 17.5

The purpose of this study was the development of a processing sequence for buried contact solar cells on multicrystalline silicon (mc-Si). The applied process includes mechanical V-texturing for the reduction of reflection losses as well as bulk passivation by a remote hydrogen plasma source. Record high efficiencies of 17.5% (V/sub /spl prop//=628 mV, J/sub sc/=36.3 mA/cm/sup 2/, FF=76.8%, independently confirmed at FhG-ISE) have been obtained on Polix mc-Si on a solar cell area of 144 cm/sup 2/. The high J/sub sc/ results from low shadowing and reflection losses, high bulk diffusion lengths and from a selective emitter structure. Hydrogenation was investigated for Baysix mc-Si and led to an increase in V/sub /spl prop// of 5-11 mV and in J/sub sc/ of 0.3-0.6 mA/cm/sup 2/, which were caused by an increase in the effective diffusion length of 40-50 /spl mu/m. It has been demonstrated, that hydrogenation from a PECVD SiN/sub x/ layer applied to screen printed solar cells could be more effective than remote plasma hydrogenation in BCSCs.

Systematic study towards high efficiency multicrystalline silicon solar cells with mechanical surface texturization

The aim of the present work was to optimize a high efficiency process for multicrystalline silicon solar cells (including Al-gettering, oxide and hydrogen passivation, Al-BSF formation, photolithographically defined front metallization) and combine it with the mechanical texturization technique. New cell structures were created, in which only the areas between the front grid are V-grooved. Solar cells were processed on various ribbon and conventional cast silicon materials. IV-characteristics, reflectance and spectral response were measured and analysed by two dimensional device simulation. A comparison with equally processed flat cells shows an increase of cell efficiencies by more than 25% due to the reduction of optical losses before antireflection coating and by an additional 4% due to the enhanced collection probability in the V-groove volumes.

Process and technology development for back contact silicon solar cells

Back contact solar cells promise several advantages over conventional solar cells such as easier module fabrication, higher efficiencies and excellent optical appearance. We investigated several industrial processing sequences for the manufacturing of emitter wrap through, metallization wrap through (/spl eta/=17.2%) and metallization wrap around (/spl eta/=17.5%) solar cells. These new devices require novel process technologies for the definition of rectifying p/n junctions on the rear. Therefore three different methods were applied in EWT solar cells: screen printed diffusion barriers (/spl eta/=16.1%, screen printed metallization, 10/spl times/10cm/sup 2/), laser patterning of a dielectric (/spl eta/=16.6%, buried contacts, 5/spl times/5cm/sup 2/) and P-Al co-diffusion (/spl eta/=10.1%, no ARC, 5/spl times/5cm/sup 2/). Additionally, the EWT concept was applied to monolithically integrated high voltage solar cells.