Efficiency enhancement in P3HT-based polymer solar cells with a NaYF ₄:2% Er³⁺, 18% Yb³⁺ up-converter

The commonly used donor material poly(3-hexylthiophene) (P3HT) confines the power conversion efficiency (PCE) in P3HT-based polymer solar cells due to its relatively large bandgap of ∼1.9 eV and the resultant limited absorption wavelength region of less than 650 nm. In this communication, the highly efficient up-conversion (UC) material NaYF₄:2% Er³⁺, 18% Yb³⁺, converting near-infrared radiation into green and red emissions, is introduced into a P3HT/P3HT:[6,6] phenyl C₆₁ butyric acid methyl ester (PC₆₁BM) bulk heterojunction solar cell, referred to as a "bilayer cell", to compensate for the non-absorbable wavelength region of P3HT. With an optimal UC doping concentration of 11.7% (weight ratio of UC to P3HT) in the P3HT matrix, the short-circuit current density and PCE for UC-doped bilayer cell are as high as 10.89 mA cm ^-2 and 3.62%, about 16.6% and 10.7% higher than the P3HT/P3HT:PC ₆₁BM bilayer cell and 22.4% and 16.4% higher than the standard P3HT:PC₆₁BM bulk heterojunction one, respectively, although the fill factor in the UC-doped bilayer cell shows a slight decrease. The research result demonstrates that both the emission and the scattering of UC nanoparticles are beneficial to the enhancement of the solar cell's electrical performances.