Thanks to the bulk-heterojunction (BHJ) feature of polymer solar cells (PSC), additional light active components can be added with ease to form ternary solar cells. This strategy has achieved great success largely due to expanded spectral response range and improved power conversion efficiency (PCE) without incurring excessive processing costs. Here, we report ternary blend polymer-polymer solar cells comprised of PTB7, P3HT, and PC 71 BM with PCE as high as 8.2%.2 Analysis from femtosecond time resolved photoluminescence and transient absorption spectroscopy confirm that P3HT is effective in transferring energy non-radiatively by inducing excitons and prolonging their overall lifetime in PTB7. Furthermore, solvent vapor annealing (SVA) treatment has been employed to improve the overly-coarse surface morphology. As a result, the fill factor and interfacial recombination has been further improved, boosting the PCE to 8.7%.
The incorporation of multiple donors into the bulk‐heterojunction layer of organic polymer solar cells (PSCs) has been demonstrated as a practical and elegant strategy to improve photovoltaics performance. However, it is challenging to successfully design and blend multiple donors, while minimizing unfavorable interactions (e.g., morphological traps, recombination centers, etc.). Here, a new Förster resonance energy transfer‐based design is shown utilizing the synergistic nature of three light active donors (two small molecules and a high‐performance donor–acceptor polymer) with a fullerene acceptor to create highly efficient quaternary PSCs with power conversion efficiencies (PCEs) of up to 10.7%. Within this quaternary architecture, it is revealed that the addition of small molecules in low concentrations broadens the absorption bandwidth, induces cocrystalline molecular conformations, and promotes rapid (picosecond) energy transfer processes. These results provide guidance for the design of multiple‐donor systems using simple processing techniques to realize single‐junction PSC designs with unprecedented PCEs.
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