Cu元素对Cu(In,Ga)Se_2薄膜及太阳电池的影响

Effects of Cu elements on Cu(In,Ga)Se_2 film and solar cell

Cu元素成分对Cu(In,Ga)Se2(简称CIGS)薄膜材料的电学性质及其电池器件性能有很重要的影响.本文利用蒸发法制备了贫Cu和富Cu的CIGS吸收层(0.7<Cu/(Ga+In)<1.15)及相应的电池器件.扫描电镜和Hall测试发现,富Cu材料的结构特性(晶粒大、结晶状态好)和电学特性(电阻率低、迁移率高等)优于贫Cu材料,而性能测试表明贫Cu器件的效率优于富Cu器件.变温性能测试分析表明,贫Cu器件的主要复合路径是体复合,激活能与CIGS禁带宽度相当;富Cu器件的主要复合路径是界面复合,其激活能远小于CIGS禁带宽度,这大大降低了开路电压Voc,从而降低了电池效率.最后利用蒸发三步法制备了体材料稍富Cu表面贫Cu的CIGS吸收层,降低了短路电流和开路电压的损失,获得了超过15%的电池效率.

The Cu elements of Cu （In, Ga） Se2 （CIGS） have very important influences on the electrical properties of CIGS absorber and solar cells. In this paper, Cu-poor and Cu-rich absorber layers （0.7＆lt;Cu/（Ga＋In） （＆lt;1.15） and solar cells are prepared by evaporation method. The SEM and Hall measurements reveal that Cu-rich material shows superior structural （larger grain size, better crystalline） and electrical （lower resistivity, higher mobility） properties to Cu-poor material. However, I-V tests show that the efficiency of Cu-poor solar cell is better than that of the Cu-rich device. The temperature-dependent I-V tests indicate that electron loss is mainly due to the bulk recombination in Cu-poor solar cell, and the activation energy of recombination is comparable to the band gap energy of Cu-poor solar cell. In contrast, in the Cu-rich devices the recombination at the heterointerface is dominant, and the activation energy is smaller than the band gap energy of the absorber material, which is an important drawback of open circuit voltage. Finally, Cu-poor surface on Cu-rich absorber is prepared by three-stage evaporation process, which reduces the short-circuit current and open-circuit voltage loss and optimizes the performance of CIGS solar cells. The efficiency of CIGS solar cell is achieved to be as high as more than 15%.