Influence of nanocrystal concentration on the performance of hybrid P3HT:TBPO-capped CdSe nanocrystal solar cells

Hybrid solar cells based on the polymer poly(3-hexylthiophene) (P3HT) and colloidal TBPO-capped CdSe nanocrystals (NCs) have been studied using varying amounts of CdSe NCs. The power conversion efficiency of these devices increased monotonically from η p = 0.05 % for 0 wt% NCs under white light illumination to 0.25 % for 40 wt% and then decreased to 0.07 % for 60 wt% NCs. The improvement in efficiency was mainly due to a remarkable increase in both the short-circuit current and open-circuit voltage, whereas the fill factor was less affected. In addition, the PL spectra of these devices showed a significant quenching suggesting rapid charge or energy transfer at the polymer–nanocrystal interface. The results indicate that capping with the smaller TBPO ligand did not considerably passivate the CdSe nanocrystal surface and the improvement in device performance could be mainly due to a pronounced PL quenching. The effect of using a relatively small TBPO compared to the commonly used TOPO ligand on the performance of these devices is discussed.