Wang Yu-Hsiang, Ho Pin-Han, Huang Wei-Chih, Tu Lung-Hsin, Chang Hsin-Fang, Cai Chung-Hao, Lai Chih-Huang
Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan.
ACS Appl Mater Interfaces. 2020 Jun 24;12(25):28320-28328. doi: 10.1021/acsami.0c07714. Epub 2020 Jun 12.
A one-step sputtering process using a quaternary target has been demonstrated to be a simple route to form Cu(In,Ga)Se (CIGSe) absorber without post-selenization; however, the lack of a Ga-grading structure in the CIGSe absorber confines its efficiency. Here, we demonstrate a one-step cosputtering process to control the Ga profile in the CIGSe absorber on flexible stainless steel substrates. Special attention was paid to the formation of second phases and their effects on the cell performance. Although the normal Ga-grading and efficiency enhancement could be achieved by cosputtering of CIGSe and GaSe targets, high-energy ion bombardment during the sputtering process might cause the decomposition of the GaSe target, leading to the formation of GaO in the CIGSe absorber, which gradually degraded the device performance. We replaced the GaSe target with a stoichiometric CuGaSe target for cosputtering, which can further enhance the cell efficiency due to the elimination of GaO. However, when the Ga content at the back side of CIGSe is further increased by raising the deposition power of the CuGaSe target, the phase separation of CuGaSe may take place, resulting in the formation of CuSe and CuGaSe at the back side of the CIGSe absorber; therefore, the recombination at the back side is increased. By cosputtering a CIGSe target with a Cu-deficient CuGaSe target, we can suppress the formation of second phases and achieve designable normal grading, leading to the highest efficiency of 15.63% without post-selenization on flexible substrates.
已证明使用四元靶材的一步溅射工艺是在不进行后硒化处理的情况下形成Cu(In,Ga)Se（CIGSe）吸收层的简单途径；然而，CIGSe吸收层中缺乏Ga梯度结构限制了其效率。在此，我们展示了一种一步共溅射工艺，用于控制柔性不锈钢衬底上CIGSe吸收层中的Ga分布。特别关注了第二相的形成及其对电池性能的影响。尽管通过CIGSe和GaSe靶材的共溅射可以实现正常的Ga梯度和效率提高，但溅射过程中的高能离子轰击可能会导致GaSe靶材分解，从而在CIGSe吸收层中形成GaO，这会逐渐降低器件性能。我们用化学计量比的CuGaSe靶材代替GaSe靶材进行共溅射，由于消除了GaO，这可以进一步提高电池效率。然而，当通过提高CuGaSe靶材的沉积功率进一步增加CIGSe背面的Ga含量时，CuGaSe可能会发生相分离，导致在CIGSe吸收层背面形成CuSe和CuGaSe；因此，背面的复合增加。通过用缺铜的CuGaSe靶材与CIGSe靶材共溅射，我们可以抑制第二相的形成并实现可设计的正常梯度，从而在柔性衬底上不进行后硒化处理的情况下实现了15.63%的最高效率。
