Efficient single and multi-junction n-i-p solar cells with high quality hot-wire microcrystalline silicon simulated using AMPS

L. STOLK, ROBERT; FRANCISCO ALBERTO RUBINELLI; H. LI,; R.H. FRANKEN,; J.K. RATH,; R.E.I. SCHROPP,

Bruselas

Congreso; ATHLET Workshop on Numerical Modelling (NUMOS); 2007

Universidad de Gent, Belgica

At the Utrecht Solar Energy Laboratory (USEL) we conduct a research program on thin filmsilicon solar cells. For tandem solar cells that were current-limited by the microcrystalline (ìc-Si:H) bottom cell, we observed that the FF-value of 0.75-0.77 was substantially higher than the value of 0.70 we obtain for single junction ìc-Si:H cells with a similar absorber layer thickness. Experiments and calculations identified the red-shifted, attenuated illumination of the bottom cell and the higher operational voltage of tandem cells as causes for the high tandem cell FF values. We performed computer simulations using the D-AMPS computer code to obtain a deeper insight into tandem cell operation. We varied the thickness of the ìc-Si:H i-layer of the bottom cell while keeping the top cell absorber layer unchanged, and calculated the illuminated J-V parameters. It was found that the tandem cell FF increases with an increasing mismatch of the subcell currents. Additionally, we calculated the charge carrier recombination profiles. With respect to the current-matched case, we found that for a bottom cell limited case the recombination rate in the top cell increases, while it decreases in the bottom cell. The difference with the matched case becomes increasingly pronounced with an increasing current mismatch. From the simulation results it is clear that a current mismatch positively influences the FF of the limiting cell and, thereby, the tandem cell FF.