1：Experimental Design and Method Selection:

The study compares TiO2- and SnO2-based planar perovskite solar cells (PSCs) to understand the influence of electron transport layers (ETLs) on charge dynamics and trap-state properties. Transient photovoltage (TPV) and transient photocurrent (TPC) measurements were conducted to explore charge carrier recombination and transport processes. Time-resolved charge extraction (TRCE) measurements were used to evaluate trap-state properties.

2：Sample Selection and Data Sources:

Perovskite films were deposited on TiO2 and SnO2 substrates. The morphologies and crystallinities of the perovskite films were characterized by field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD).

3：List of Experimental Equipment and Materials:

FE-SEM (Hitachi SU8010), XRD (Shimadzu XRD-7000), UV-vis spectrometer (Shimadzu UV-3600), steady-state PL spectroscopy (Edinburgh FLS980 spectrometer), solar simulator, sourcemeter (Keithley 2400), digital oscilloscope (64Xs, Lecroy).

4：Experimental Procedures and Operational Workflow:

PSCs were fabricated by sequentially coating FTO glass substrates with compact TiO2 and SnO2 thin films, followed by perovskite precursor deposition. The hole transport layer was spin-coated after thermal annealing of the perovskite active layer. Au was thermally evaporated as the counter electrode.

5：Data Analysis Methods:

The photovoltage decay traces were fitted with a bi-exponential function to calculate recombination and transport time constants. The extracted charge at different photovoltages was obtained by integrating the extraction current curves.