Centro de Investigación, Innovación y Desarrollo de Materiales - CIDEMAT, Facultad de Ingeniería, Universidad de Antioquia UdeA, Calle 70 No. 52-21, Medellín, Colombia.
Nanoscale. 2017 Jul 13;9(27):9440-9446. doi: 10.1039/c7nr01678f.
Effective control of the interface between the metal cathode and the electron transport layer (ETL) is critical for achieving high performance p-i-n planar heterojunction perovskite solar cells (PSCs). Several organic molecules have been explored as interlayers between the silver (Ag) electrode and the ETL for the improvement in the photovoltaic conversion efficiency (PCE) of p-i-n planar PSCs. However, the role of these organic molecules in the charge transfer at the metal/ETL interface and the chemical degradation processes of PSCs has not yet been fully understood. In this work, we systematically explore the effects of the interfacial modification of the Ag/ETL interface on PSCs using rhodamine 101 as a model molecule. By the insertion of rhodamine 101 as an interlayer between Ag and fullerene derivatives (PC60BM and PC70BM) ETLs improve the PCE as well as the stability of p-i-n planar PSCs. Atomic force microscopy (AFM) characterization reveals that rhodamine passivates the defects at the PCBM layer and reduces the band bending at the PCBM surface. In consequence, charge transfer from the PCBM towards the Ag electrode is enhanced leading to an increased fill factor (FF) resulting in a PCE up to 16.6%. Moreover, rhodamine acts as a permeation barrier hindering the penetration of moisture towards the perovskite layer as well as preventing the chemical interaction of perovskite with the Ag electrode. Interestingly, the work function of the metal cathode remains more stable due to the rhodamine incorporation. Consequently, a better alignment between the quasi-Fermi level of PCBM and the Ag work function is achieved minimizing the energy barrier for charge extraction. This work contributes to reveal the relevance of proper interfacial engineering at the metal-cathode/organic-semiconductor interface.
有效控制金属阴极和电子传输层（ETL）之间的界面对于实现高性能的 p-i-n 平面异质结钙钛矿太阳能电池（PSC）至关重要。已经探索了几种有机分子作为银（Ag）电极和 ETL 之间的层间材料，以提高 p-i-n 平面 PSC 的光伏转换效率（PCE）。然而，这些有机分子在金属/ETL 界面处的电荷转移以及 PSC 的化学降解过程中的作用尚未得到充分理解。在这项工作中，我们使用罗丹明 101 作为模型分子，系统地研究了 Ag/ETL 界面的界面修饰对 PSC 的影响。通过将罗丹明 101 插入 Ag 和富勒烯衍生物（PC60BM 和 PC70BM）ETL 之间作为层间材料，可以提高 p-i-n 平面 PSC 的 PCE 和稳定性。原子力显微镜（AFM）表征表明，罗丹明可以钝化 PCBM 层中的缺陷，并减少 PCBM 表面的能带弯曲。因此，来自 PCBM 的电荷转移到 Ag 电极增强，导致填充因子（FF）增加，从而使 PCE 提高至 16.6%。此外，罗丹明作为渗透障碍，阻止水分向钙钛矿层渗透，并防止钙钛矿与 Ag 电极的化学相互作用。有趣的是，由于罗丹明的掺入，金属阴极的功函数保持更稳定。因此，实现了 PCBM 的准费米能级和 Ag 功函数之间更好的对准，最小化了电荷提取的能量势垒。这项工作有助于揭示金属阴极/有机半导体界面适当的界面工程的相关性。
