LABORATORI NAZIONALI DI LEGNARO
The organic, polymer-based photovoltaic elements have introduced the potential of obtaining cost effective and easy methods to produce energy from light. Apart from low cost of synthesis and ease of fabrication, organic semiconductor thin films may show high absorption coefficients exceeding 105 cm-1, which makes them good chromophores for optoelectronic applications. The transport properties of thin film devices made out of them are well characterized by using space charge limited current models with field dependent mobilities. On the other hand the temperature dependence thin film of inorganic nanocrystals has been observed to be thermally activated. However, the energetic disorder arises from the size distribution of the particles and geometric disorder from the separation of the particles, spatially or by ligands It is of particular interest to study the transport in Organic / inorganic (poly3-hexyl thiophene (P3HT)/CdS, P3HT-CdTe) hybrid systems, as the power conversion efficiency of such hybrid system is far better than of pure P3HT. These systems represent the combination of disordered transport in organic materials and band like transport in inorganic semiconductors. In P3HT the charge carrier mobility is dependent on temperature, carrier density, and applied fields given by unified mobility model. We observed that the incorporation of CdTe / CdS nanocrystals results into enhancement of current density, attributed to increase in the value of trap density and decrease of activation energies. The hole mobility is observed to be independent to charge carrier density and applied field and depends only on temperature. It is suggested that holes had to jump from one polymer chain to other through P3HT are now assisted by CdTe / CdS nanocrystals. The switching of mobility model in P3HT to band conduction mechanism in composites is probably due to improvement in electron wave function overlap between two polymer chains. As a result, charge carriers drift rather than hopping in the extended states of P3HT and valence bands of CdTe / CdS.

DATA: 18-05-2012