Mid-gap trap states in CdTe nanoparticle solar cells

Abstract

Thin film solar cells comprised of quantum-confined CdTe nanoparticles are shown to have a low intrinsic density of mid-gap trap states relative to their equivalent bulk film, indicating that the ligands are effective at electrically passivating surface states. Sintering the nanoparticles into a poly-crystalline thin film increases device performance but also increases the density of mid-gap trap states due to doping from the CdCl treatment and the formation of long range disorder such as grain boundaries and dislocations. Long term aging under illumination increases the density of mid-gap traps in the unsintered films due to degradation of the ligands.