Scale-up of bulk-heterojunction polymer solar cells

Polymer solar cells (PSCs) have recently reported a marked improvement in conversion efficiency, exceeding 10%, thus reducing the gap with more mature photovoltaic technologies. Now the transfer of such performances to the large scale has to be carried out by using industrially relevant techniques such as spray and slot die coating, and inkjet, gravure, flexographic and screen printing. This work is focused on the scale up of the PSCs by exploiting spray coating, a simple and low cost method already successfully applied to PSC layers. Firstly in literature a fully sprayed module was fabricated on glass substrate by an automated machine in air. Moreover, modules comprising a sprayed active layer were realized on flexible substrates. Both of them yielded ~1% of efficiency and supplied small power electronic devices. The aim to increase the efficiency of the modules addressed the activity towards two aspects. The first one concerned the investigation of new sprayable materials, i.e. low-temperature TiOX and PFN as interlayers and PBDTTT-C-T:PC71BM as active layer, all processed in safe solvents. The second one regarded the influence of the patterning methods, such as mechanical scribing and additive patterning through aerosol jet pre-printing, on the electrical parameters of the device. Finally, a lot of attention was focused on the stability issue. Encapsulation with commercial polymers was employed by heat sealing and this method revealed to be effective in the assembly of a fully solution-processed panel for greenhouse applications. Furthermore, the intrinsic stability of the device structure was analyzed; it was demonstrated that the electron transport layer and the solvent in which it is dissolved have a great influence on the device stability.