在N型PERT太阳电池制备过程中,蒸镀铝可作为太阳电池背面的金属电极,但是由于背面激光开膜所引起的氧化层会影响太阳电池的串联电阻(R_s),所以必须在蒸镀铝工序完成后对太阳电池进行退火处理以减少Rs。文章重点研究了以蒸镀铝为背电极的N型PERT太阳电池在不同退火工艺下的性能差异,研究结果表明,退火温度不变,随着退火时间的增加,Rs逐渐降低,填充因子(FF)和短路电流密度(J_(sc))迅速升高,开路电压(V_(oc))则缓慢升高,如果退火时间恰当,R_s会降得很低,V_(oc)也会处于峰值,此时电池效率(E_(ta))最大,最终在退火温度为380℃,且退火时间为40 s时,太阳电池的E_(ta)可达到20.77%。通过研究发现:太阳电池的退火过程可用阿伦尼乌斯公式来表达,通过此方程得出了铝和氧化硅退火反应的表观活化能为91.89 k J/mol。
Atom layer deposition(ALD)-Al2O3 thin films are considered effective passivation layers for p-type silicon surfaces. A lower surface recombination rate was obtained through optimizing the deposition parameters. The effects of some of the basic substrate characteristics including material type, bulk resistivity and surface morphology on the passivation performance of ALD-Al2O3 are evaluated in this paper. Surface recombination velocities of 7.8 cm/s and 6.5 cm/s were obtained for p-type and n-type wafers without emitters, respectively. Substrates with bulk resistivity ranging from 1.5 to 4Ω·cm were all great for such passivation films, and a higher implied Voc of 660 mV on the 3Ω·cm substrate was achieved. A minority carrier lifetime(MCL) of nearly 10 μs higher was obtained for cells with apolished back surface compared to those with a textured surface,which indicates the necessity of the polishing process for high-efficiency solar cells. For n-type semi-finished solar cells, a lower effective front surface recombination velocity of 31.8 cm/s was acquired, implying the great potential of(ALD)-Al2O3 thin films for high-efficiency n-type solar cells.
