Spectroscopic and electrical properties of hybrid thin films for solar cell applications

Colloidal CuInS2 nanocrystals (CIS NCs) are one of the most interesting absorbing materials in bulk heterojunction (BHJ) solar cells due to their low toxicity and wide absorption range. However, despite much research on this topic, the performance of CIS NC–based hybrid solar cells remains low so far. One of the important issues in CIS/polymer BHJ solar cells are the surface properties of CIS NCs. It is well known that ligands can be used to improve the stability of the synthesized CIS nanoparticles in order to prevent their aggregation during solar cell fabrication. On the other hand, these ligands can have a disadvantageous influence on the charge transfer processes between CIS NCs and polymers and the charge transport properties of CIS NCs. A simple method to investigate the charge transport in thin films of CIS NCs is by single carrier (i.e., hole- and electron-only) devices. The charge transfer processes in hybrid polymer/NC solar cells were studied by quasi-steady-state photoinduced absorption and photoluminescence quenching. These techniques provided evidence of long-lived polarons and excited state dynamics indicating the occurrence of charge separation and transfer in polymer/NCs system.