Electron Transport Layers in Perovskite Solar Cells

In recent years, the power conversion efficiency of perovskite solar cells has increased substantially, reaching today's values of above 25%. This has also placed an increased focus on device stability, which still limits commercial use. Electron transport layers (ETL) are critical for both factors in perovskite solar cells and have received much attention since the research focus boomed for this technology. In this chapter, requirements on ideal ETL are first provided, including electronic and photonic properties, energy band alignment, morphology, defect states, and chemical stability. Different metal oxide and organic electron transport materials used for perovskite solar cells are reviewed, focusing on optimizing ETL using various doping strategies to improve the cells' efficiency. Finally, the progress made on electron transport materials used in mesoscopic perovskite solar cells, as well as normal (n–i–p) and inverted (p–i–n) planar perovskite solar cells is briefly discussed, highlighting device architecture considerations. This chapter reviews the ETL used in perovskite solar cells, emphasizing the considerations needed when embedding such layers inside perovskite solar cells.