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 C60-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 (FA0.8Cs0.2Pb(I0.8Br0.2)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 (τex ≈ 10 ns) with high quenching efficiency (93%), together with suppressed interfacial charge recombination characterized by an extended recombination time constant (τCR ≈ 3.5 μs) compared with the C60 counterpart (τex ≈ 39 ns, τCR ≈ 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.