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Institut Silizium-Photovoltaik

Optimisation of saw damage removal to reduce interface recombination losses

The complete removal of the saw damage decreases density of states in the near surface region is an important precondition to reduce recombination losses in solar cells. In order to avoid expensive and time consuming lapping and polishing processes, wet-chemical etching procedures in alkaline potassium hydroxide (KOH) solution are preferred in solar cell manufacturing, to remove saw damage from the as-cut wafers.

saw damage

Saw Damage Etching (SDE) decreases step-wise the recombination losses. Too long SDE, however, increases surface defects and recombination losses due to inhomogeneous etching and initial formation of random pyramids. The etching time influences the saw etching dept, as well as the emerging Si surface morphology. Therefore, the SDE process has to be carefully optimised with respect to the kind of Si substrate manufacturing.


Fig. 1a Saw damage on as cut Si solar cell substrates

sde trans

Fig. 1 b Change of time decay of SPV pulses on as cut p-type CZ Si during saw damage etching (SDE) in KOH solution 


Fig. 2a Flat Si substrate surface after SDE

Fig. 2b  Dit(E) after short (curves 1, 3)  and completed (curves 2, 4) SDE and subsequent cleaning in RCA + HF (curves 1, 2) and additional smoothing in H2SO4:H2O2 + HF (curves 3, 4).

Publikationen

  • Angermann, H.; Laades, A.; Kegel, J.; Klimm, C.; Stegemann, B.: Improvement of silicon solar cell substrates by wet-chemical oxidation studied by surface photovoltage measurements. Solid State Phenomena 219 (2015), p. 291-296
  • Stegemann, B.; Kegel, J.; Mews, M.; Conrad, E.; Korte, L.; Stürzebecher, U.; Angermann, H.: Evolution of the charge carrier lifetime characteristics in crystalline silicon wafers during processing of heterojunction solar cells. Energy Procedia 55 (2014), p. 219–228
  • Kegel, J.; Angermann, H.; Stürzebecher, U.; Conrad, E.; Korte, L.; Stegemann, B.: IPA-free textured a-Si:H/C-Si heterojunction solar cells exceeding 20 % efficiency. In: Proc 28th European Photovoltaic Solar Energy Conference (2013), 2013.
  • Angermann, H.; Laades, A.; Stürzebecher, U.; Conrad, E.; Klimm, C.; Schulze, T.F.; Jacob, K.; Lawerenz, A.; Korte, L.: Wet-chemical preparation of textured silicon solar cell substrates: Surface conditioning and electronic interface properties. Solid State Phenomena 187 (2012), p. 349-352