Progress in high-efficiency emitter-wrap-through cells on medium quality substrates

One of the most promising cell concepts for high efficiencies on medium quality base material is the emitter-wrap-through (EWT) solar cell [1]. We fabricated solar cells on 1.25 Omega cm FZ and 1.4 Omega cm Cz(B) material. The performance of EWT, rear contacted cells (RCC) and random-pyramids passivated emitter and rear cells (RP-PERC) on Cz-Si is compared. An EWT efficiency of 18.7% on degraded Cz (tau(b) < 35 mus, W = 250 mum) outperforms clearly the RCC (14.9%) and even the RP-PERC (18.1%). Spectral response measurements prove the very good collection efficiency of the EWT cells compared to RCC. The cell parameters V-oc, j(sc) and eta of EWT and RCC are logged over the entire degradation process and can be fitted very well by a double exponential decay. The high potential for fill factor and therefore efficiency improvement is shown via Suns-V-oc-measurements which indicate a series resistance free fill factor of more than 81%.