Spectroscopic Investigation of Interfacial Electron Extraction and Recombination at Azaacene-Based ETLs in Perovskite Solar Cells

Despite rapid progress in halide perovskite solar cells, distinguishing interfacial charge-transfer processes from bulk transport and recombination dynamics remains challenging, limiting a quantitative understanding of transport-layer performance. In particular, the inherent limitations of C 60 -based electron transport layers (ETLs), including limited structural tunability, parasitic absorption in the visible region, and interfacial recombination losses, motivate a mechanistic investigation of alternative nonfullerene n -type materials. Here, we investigate interfacial electron transfer and recombination dynamics at the mixed-halide perovskite (FA 0.8 Cs 0.2 Pb(I 0.8 Br 0.2 ) 3, PVSK)/ETL interface using a nonfullerene n -type molecule, a tricyano-substituted diquinoxalino-phenazine derivative (CN3). Complementary flash-photolysis time-resolved microwave conductivity (FP-TRMC) and time-resolved photoluminescence (TR-PL) measurements enable decoupling of interfacial electron extraction from bulk carrier transport, revealing that PVSK/CN3 exhibits rapid interfacial electron extraction (τ ex ≈ 10 ns) with high quenching efficiency (93%), together with suppressed interfacial charge recombination characterized by an extended recombination time constant (τ CR ≈ 3.5 μs) compared with the C 60 counterpart (τ ex ≈ 39 ns, τ CR ≈ 540 ns). This work establishes a spectroscopic framework for separating interfacial charge transfer from bulk transport and provides practical design guidelines for high-performance nonfullerene ETLs.