Digitally printed photovoltaic devices with increasing stack complexity

Solution processing of OPVs on industrial scale brings some challenges, such as finding alternative, non-chlorinated solvents and using roll-to-roll compatible processes. Here we present a fully inkjet printed tandem OPV device, which consists of up to 9 sequentially inkjet printed layers. The inkjet printed layers are made without chlorinated solvents using an industrial scale printhead, making the processing industrial viable.
The main challenge for inkjet printing this tandem structure was to find a good way to print the recombination contact consisting of a closed PEDOT:PSS layer from a water based solution onto a hydrophobic P3HT:PCBM layer and on top of that a ZnO layer. Previously it was shown by our group that ZnO can be inkjet printed on a PEDOT:PSS layer, however, when modifying (commercial) PEDOT:PSS formulations the resulting surface energy of this PEDOT:PSS layer changes and hence the printability of ZnO on top of the PEDOT:PSS is different. Careful optimization of the full recombination contact was done and tandem devices were successfully inkjet printed.
The voltage of the inkjet printed tandem we present here is the sum of the voltages of the subcells, which shows that there are no voltage losses over the recombination contact. The efficiency of the inkjet printed tandems was higher than the efficiencies of the respective single junction devices. These results show that inkjet printing is a promising technique to up-scale the production of tandem OPVs and commercialization is one step closer.