Efficiency enhancement in P3HT-based polymer solar cells with a NaYF4:2% 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 similar to 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 C-61 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:PC61BM 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.