Study of Nano Morphology of Organic Hybrid Material for Solar Cell

This work presents the study of nano morphology of organic hybrid material for solar cell, trying to improve the performance of hybrid solar cells.
First, we investigated the effect of annealing process on the performance of photovoltaic devices based on P3HT/PCBM hybrid materials by monitoring the changes of nanoscale morphology and optical properties. The thermal AFM provides valuable information of morphology evolution quantitatively for the P3HT/PCBM film during the annealing process. We also correlated the morphology evolution and absorption behavior by using scanning near field optical microscopy (SNOM). The results help to determine an optimized annealing process for high performance solar cell. And from this study, we found the PCBM is not thermal stable at 140℃ for 60 minutes. The PCBM aggregates that disruptes the bicontinuous phase and reduces the performance of solar cell.
Due to the low cost and good thermal stability of TiO2 nanoparticle , we devote our study to the conducting polymer hybrided with TiO2 nanorods system. We first reveal the good thermal stability of TiO2 hybrid system. And we have synthesized a novel conducting surface ligands of carboxylic terminated oligomer (oligomer 3-hexyl thiophene -COOH) to modify the surface of the TiO2 nanorods. We studied the UV and PL properties of the hybrid made from P3HT and oligomer 3HT-COOH modified TiO2 nanorods. The results indicate the oligomer 3HT-COOH improves the charge separation of the hybrid material as compared with insulating oleic acid ligand. The performance of the solar cell can be significantly improved by 5 folds using oligomer 3HT-COOH modified TiO2 nanorod.
Finally, we used poly(3-hexylthiophene) as the buffer layer between electron blocking layer (PEDOT:PSS) and active layer (P3HT/TiO2). The inserted layer can prevent TiO2 nanorods from touching the PEDOT:PSS layer that results in short circuit. Besides, the buffer layer can facilitate the separation and transport of charge carriers efficiently that improve the performance of solar cell.