Inkjet-Printed Tin Oxide as Hole Blocking Layer for Organic Photodiodes

Organic Photodiodes (OPDs) are receiving increased research attention as they have promising applications in optical light detection for healthcare, communication and industrial monitoring. State-of-the-art OPDs currently reach responsivities that can be compared to silicon photodetectors and, additionally, offer the advantage of flexibility and tunabilty of the spectral responsivity by the choice of organic material in the bulk-heterojunction. Moreover, the possibility of solution-processing enables the use of (digital) printing techniques like inkjet-printing which offers great freedom of design and scalability. However, for fully-printed high performance OPDs, there is still the need of blocking layers to suppress parasitic charge injection which are simultaneously compatible with the processing of the device stack.<br/><br/>Here, we report the inkjet-printing of SnO2 nanoparticles (NP) used as a hole blocking material in OPDs with state-of-the-art performance. The addition of SnO2 leads to devices featuring low dark currents of ~ 5 nA/cm2, good carrier blocking behavior and stability against UV illumination compared to other materials such as ZnO. The developed printing process of SnO2 was tuned by the addition of a second solvent (diethylene glycol) and the influence of the printing drop spacing on the device performance was investigated by characterizing the OPDs’ figures of merit. A homogeneous and thin, but pinhole-free layer could be printed with the optimized printing settings (i.e. 35μm drop spacing) resulting in spectral responsivities &gt; 0.5 AW and operational speeds of up to 2 MHz. The homogeneity of the optimized film could also be linked to the best device performance of the P3HT:IDTBR OPDs. Overall, we could show the successful implementation of a printed carrier blocking material for OPDs. This processing could be adaptable to other material systems and applications.