Advanced Functional Materials, Vol.24, No.25, 3986-3995, 2014
Optimization of the Power Conversion Efficiency of Room Temperature-Fabricated Polymer Solar Cells Utilizing Solution Processed Tungsten Oxide and Conjugated Polyelectrolyte as Electrode Interlayer
The utilization of a conjugated polyelectrolyte-ionic liquid crystal (CPE-ILC) complex as electron transporting layer (ETL) to improve the compatibility between the ITO and hydrophobic active layer and to promote the dipole orientation at cathode interface is reported. Simultaneously, a hole transporting layer (HTL) of solution processed tungsten oxide together with poly(2,6-bis(trimethyltin)-4,8-bis(5-(2-ethylhexyl) thiophen-2-yl) benzo[1,2-b: 4,5-b'] dithiophene-alt-4,6-Dibromo-thieno[3,4-b] thiophene-2-carboxylic acid 2-[2-(2-methoxy-ethoxy)-ethoxy]-ethyl ester) (PBDTT-TT-TEG) efficiently shifts the work function of Ag electrode in this device. The interfacial modification of these interlayers achieves energy alignment at both electrodes. The power conversion efficiency (PCE) of the PSC based on ITO/PFN-CbpSO/PBDTTT-C-T:PC70BM/PBDTT-TT-TEG/WO3/Ag with solution processed interlayers reaches to 7.8%. It is worthy to note that except for the electrodes, all layers of device are fabricated by solution process at room temperature and without annealing. In the case of incorporating ZnO layer into this device, the device efficiency further increases to 8.5%, which is the best value reported from PBDTTT-C-T:PC70 BM-based solar cells with solution processed interlayers at both electrodes so far.