基于磁场调控Ni纳米薄带增强空穴收集的钙钛矿太阳电池研究

Perovskite solar cells have attracted significant research interests owing to their potential for low-cost fabrication, high power conversion efficiency and compatibility with flexible plastic substrates in recent years. A p-type organic small molecular, 2,2',7,7′-tetrakis (N,N-di-p-methoxyphenylamine)-9,9′ spirobifluorene (spiro-OMeTAD) is usually used as hole-transport layer in perovskite solar cells. For the further improvement of photoelectric conversion efficiency, Li-bis(trifluoromethane)sulfonyimide and 4 tert-butyl pyridine are often added into spiro-OMeTAD, to improve conductivity and suppress the recombination of photoproduced electron-hole, respectively. However, such doping would induce corrosion and degradation of optical absorption layer with perovskite structure when exposed to moisture in the air, consequently decrease device stability. This project presents magnetic field control-based hole transport composite materials consisting of spiro-OMeTAD and Ni nanobelts. Ni nanobelts array with high orientation can act as highly efficient channels of hole-collecting owning to the matching energy band between the Ni nanobelts and spiro-OMeTAD. The hole transporting distance can be reduced，thus speeding up the process of transferring hole to Ni counter electrode. It is expected to obtain a novel solar cell with high conversion efficiency and long-term stability. This research is of great significance in science for understanding the charge transfer mechanism in perovskite solar cells.

由于成本低、转换效率高且能在柔性衬底集成等优势，近年来钙钛矿太阳能电池成为研究热点。p型有机小分子2,2',7,7'-四[N,N-二（4-甲氧基苯基）氨基]-9,9'-螺二芴（spiro-OMeTAD）常作为钙钛矿太阳能电池内部的空穴传输层。为了进一步提升光电转换效率，spiro-OMeTAD中常掺入双三氟甲烷磺酰亚胺锂和四叔丁基吡啶，分别起到提高电导率和抑制载流子复合的作用。然而，掺杂会促进钙钛矿光吸收层的腐蚀和吸湿降解，从而降低电池的稳定性。本项目提出一种基于磁场调控的spiro-OMeTAD/ Ni纳米薄带复合空穴传输材料。凭借Ni纳米薄带与spiro-OMeTAD的能带匹配及磁场调控取向，Ni纳米薄带阵列可以充当高效的空穴收集通道，缩短了空穴传输距离，进而加快传递到Ni背电极，有望增加效率的同时提升稳定性。这项研究对于认识钙钛矿太阳能电池内部电荷输运机制具有重要的科学意义。

经过十几年的研究发展，钙钛矿太阳电池的能量转换效率已从最初的3.8%迅猛提升到25.5%，成为第三代太阳电池中最有潜力的竞争者。然而，距离肖特基/奎塞尔理论极限（33%）仍有一定距离。实际上，电荷传输层与钙钛矿层间非平衡的电荷传输性能极大阻碍了电池性能的进一步提升。增强空穴输运性能显得尤为重要。本项目提出以镍纳米薄带作为空穴传输通道，有助于缩短空穴到达电极的传输距离，实现空穴的快速传递，减少电子空穴复合几率，提高能量转换效率。此外，光生空穴从钙钛矿层注入到空穴传输层的能力也是影响空穴收集的重要因素之一。研究发现在钙钛矿/空穴传输层界面存在大量的缺陷，成为光生电荷复合的“重灾区”，严重影响空穴在界面处的注入效率，这对器件效率及稳定性均会造成不利影响。为此，本项目研发了六种新型缺陷态钝化剂（氟化黑磷纳米薄片、交联硫辛酸、氟化石墨烯量子点、N,S共掺杂石墨烯量子点、辛基碘化铵、羟基氧化铁），开展多界面缺陷态钝化的研究工作。可获得如下优势：①有效减缓钙钛矿的晶化过程，获得均匀致密的大晶粒钙钛矿薄膜，提高成膜质量；②有效阻止离子迁移，减少在晶界和电荷传输界面处留下的空位缺陷态；③钝化剂可填补因化学配比失衡或离子迁移产生的空位，降低载流子被捕获的几率。经过系统优化设计，改善了器件的环境稳定性，进一步降低J-V滞回，显著提升能量转换效率，可达到22.06%。本项目的研究成果对于推动钙钛矿太阳能电池的商业化应用具有重要的现实意义。