Sadegh Faranak, Akman Erdi, Prochowicz Daniel, Tavakoli Mohammad Mahdi, Yadav Pankaj, Akin Seckin
Department of Chemistry, University of Isfahan, Isfahan 81746-73441, Iran.
Laboratory of Photovoltaic Cells (PVcells), Karamanoglu Mehmetbey University, 70200 Karaman, Türkiye.
ACS Appl Mater Interfaces. 2022 Aug 31;14(34):38631-38641. doi: 10.1021/acsami.2c06110. Epub 2022 Aug 18.
Electron transporting layer (ETL)-free perovskite solar cells (PSCs) exhibit promising progress in photovoltaic devices due to the elimination of the complex and energy-/time-consuming preparation route of ETLs. However, the performance of ETL-free devices still lags behind conventional devices because of mismatched energy levels and undesired interfacial charge recombination. In this study, we introduce sodium fluoride (NaF) as an interface layer in ETL-free PSCs to align the energy level between the perovskite and the FTO electrode. KPFM measurements clearly show that the NaF layer covers the surface of rough underlying FTO very well. This interface modification reduces the work function of FTO by forming an interfacial dipole layer, leading to band bending at the FTO/perovskite interface, which facilitates an effective electron carrier collection. Besides, the part of Na ions is found to be able to migrate into the absorber layer, facilitating enlarged grains and spontaneous passivation of the perovskite layer. As a result, the efficiency of the NaF-treated cell reaches 20%, comparable to those of state-of-the-art ETL-based cells. Moreover, this strategy effectively enhances the operational stability of devices by preserving 94% of the initial efficiency after storage for 500 h under continuous light soaking at 55 °C. Overall, these improvements in photovoltaic properties are clear indicators of enhanced interface passivation by NaF-based interface engineering.
无电子传输层（ETL）的钙钛矿太阳能电池（PSC）由于省去了复杂且耗能/耗时的ETL制备工艺，在光伏器件方面展现出了良好的进展。然而，无ETL器件的性能仍落后于传统器件，这是由于能级不匹配以及不良的界面电荷复合所致。在本研究中，我们将氟化钠（NaF）引入无ETL的PSC中作为界面层，以调整钙钛矿与FTO电极之间的能级。开尔文探针力显微镜（KPFM）测量清楚地表明，NaF层能很好地覆盖粗糙的底层FTO表面。这种界面修饰通过形成界面偶极层降低了FTO的功函数，导致FTO/钙钛矿界面处的能带弯曲，这有利于有效的电子载流子收集。此外，发现部分Na离子能够迁移到吸收层中，促进钙钛矿层晶粒增大和自发钝化。结果，经NaF处理的电池效率达到20%，与基于ETL的最先进电池相当。此外，该策略通过在55°C连续光照浸泡500小时后仍保持94%的初始效率，有效地提高了器件的运行稳定性。总体而言，光伏性能的这些改善清楚地表明基于NaF的界面工程增强了界面钝化。
