Jiangsu Key Laboratory for Carbon-Based Functional Materials and Devices, Institute of Functional Nano & Soft Materials (FUNSOM), Soochow University , Suzhou 215123, China.
ACS Nano. 2017 Jul 25;11(7):7215-7222. doi: 10.1021/acsnano.7b03090. Epub 2017 Jul 11.
Silicon-organic heterojunction solar cells suffer from a noticeable weakness of inefficient rear contact. To improve this rear contact quality, here, two solution-processed organic n-type donor-acceptor naphthalene diimide (NDI)-based conjugated polymers of N2200 and fluorinated analogue F-N2200 are explored to reduce the contact resistance as well as to passivate the Si surface. Both N2200 and F-N2200 exhibit high electron mobility due to their planar structure and strong intermolecular stacking, thus allowing them to act as excellent transporting layers. Preferential orientation of the polymers leads to reduce contact resistance between Si and cathode aluminum, which can enhance electron extraction. More importantly, the substitution of fluorine atoms for hydrogen atoms within the conjugated polymer can strengthen the intermolecular stacking and improve the polymer-Si electronic contact due to the existence of F···H interactions. The power conversion efficiencies of Si-PEDOT:PSS solar cells increased from 12.6 to 14.5% as a consequence of incorporating the F-N2200 polymer interlayers. Subsequently, in-depth density functional theory simulations confirm that the polymer orientation plays a critical role on the polymer-Si contact quality. The success of NDI-based polymers indicates that planar conjugated polymer with a preferred orientation could be useful in developing high-performance solution-processed Si-organic heterojunction photovoltaic devices.
硅-有机杂化异质结太阳能电池存在后接触效率低下的明显弱点。为了改善这种后接触质量，本文探索了两种可溶液加工的有机 n 型给体-受体萘二酰亚胺（NDI）基共轭聚合物 N2200 和氟化类似物 F-N2200，以降低接触电阻并钝化 Si 表面。由于其平面结构和强分子间堆积，N2200 和 F-N2200 都表现出高电子迁移率，因此它们可以作为优秀的传输层。聚合物的优先取向可以降低 Si 和阴极铝之间的接触电阻，从而增强电子提取。更重要的是，在共轭聚合物中用氟原子取代氢原子可以通过 F···H 相互作用增强分子间堆积并改善聚合物-Si 电子接触。Si-PEDOT：PSS 太阳能电池的功率转换效率从 12.6%提高到 14.5%，这是由于掺入了 F-N2200 聚合物层。随后，深入的密度泛函理论模拟证实了聚合物取向对聚合物-Si 接触质量起着关键作用。基于 NDI 的聚合物的成功表明，具有优先取向的平面共轭聚合物在开发高性能溶液处理的 Si-有机杂化光伏器件方面可能是有用的。
