Enhanced performance of the nanostructured zinc oxide-conjugated polymer based hybrid solar cell with the application of a low band gap co-polymer

The introduction of low band-gap, donor-acceptor (D-A) co-polymer in nanostructured zinc oxide/conjugated polymer based solar cell in place of usual conjugated homo-polymer boosts up the device performance. In this work, we have used co-polymer PCDTBT (Poly [[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thophenediyl-2,1,3- benzothiadiazole-4,7-diyl-2,5-thiophenediyl]) as the active material in the solar cells. PCDTBT energetically fits with the energy levels of the ZnO for forming an ideal heteorojunction in inverted solar cell and showed better device efficiency. We further study the annealing effect on the device performance with a range of annealing temperatures. The device performance improved significantly up to a certain temperature. The absorption spectra of the PCDTBT with different annealing temperature were carried out to study the charge transfer (CT) excitons absorption profile and how it is affected by temperature. The CT exciton dissociation and the photo physics of the charge transport were investigated to understand the major reason for the better device performance in this case even without blending the fullerene with the polymer.