Efficient Electron Transport Layer-Free Perovskite Solar Cells Enabled by Discontinuous Polar Molecular Films: A Story of New Materials and Old Ideas?
Like Huang, Jiaming Huang, Ruixiang Peng, Ziyi Ge
Abstract
Interests in minimalist device structure design of perovskite solar cells (PSCs) have accelerated the rapid advances of electron transport layer-free PSCs by composition and solvent engineering. For higher device performance, interface engineering regarding effective interface energy level alignment is highly needed. Herein, a polar nonconjugated small-molecule electrolyte (PNSME) inter-layer is inserted into the perovskite/indium tin oxide (ITO) interface to reduce the carrier collection barrier at this interface. By changing the inter-layer thickness, ITO’s effective work function and thus the energy level alignment at the perovskite/ITO interface can be continuously controlled. Interestingly, although pinholes are found in all discontinuous inter-layers with varying thicknesses, they hardly affect the uniformity of ITO’s local work function distribution. According to the PNSME thickness and coverage, two coexisting mechanisms of interface electron injection are proposed. The interfacial dipoles of the inter-layer are of great significance with respect to electron tunneling through PNSME with a typical quantum mechanical tunneling thickness limit of ∼10 nm, whereas electron transmission through the thick inter-layer (≥10 nm) is dominated by the direct perovskite/ITO contact at the pinhole area. This work provides novel insights on the work principle of PSCs and highlights the importance of interface engineering of perovskite/ITO contact toward efficient and simple-structured PSCs.