1：Experimental Design and Method Selection:

The study involves the construction of triple-junction polymer solar cells (TJ-PSCs) with varied subcells to study the impact of middle cell selection on overall device performance. Optical modeling based on the transfer matrix method is used to probe optimal thicknesses of subcells.

2：Sample Selection and Data Sources:

The study uses fullerene- and nonfullerene-based absorbers in a designed multijunction architecture. Single-junction PSCs are first studied to characterize each BHJ blend.

3：List of Experimental Equipment and Materials:

The functional interconnection layer (ICL) is fabricated in the structure of MoO3/ultrathin Ag (0.6 nm)/zinc oxide nanoparticles (ZnO-NP)/PFN-Br. A spectroscopic ellipsometer is used to measure the refractive index (n) and extinction coefficient (k) of different layers.

4：6 nm)/zinc oxide nanoparticles (ZnO-NP)/PFN-Br. A spectroscopic ellipsometer is used to measure the refractive index (n) and extinction coefficient (k) of different layers. Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: TJ-PSCs are constructed with the structure of ITO/ZnO/PBDB-T-2F: PC71BM/ICL/PBDB-T: ITIC (or PBDB-T: HF-TCIC)/ICL/PTB7-Th: IEICO-4F/MoO3/Ag. The layer thicknesses of the front, middle, and rear cells are carefully tuned under the guidance of optical simulation.

5：Data Analysis Methods:

External quantum efficiencies (EQEs) of different SJ-PSCs are measured. Optical modeling and energy loss analysis are conducted to evaluate the performance of TJ-PSCs.