Aerosol‐Jet‐Printed Donor‐Blocking Layer for Organic Photodiodes

Abstract

Organic photodiodes (OPDs) are optical sensors combining high performance, lightweight mechanical flexibility, and processability from solution. Their fabrication by industrial printing techniques opens a wide range of innovative applications for emerging fields in sensing and the Internet of Things. They typically consist of printed multilayers with functionalities to absorb light, to extract charges, or to reduce detection noise. However, the printing of such device architecture poses a challenge as the deposition of a material can lead to disruption of film morphology or intermixing of materials if its solvent interacts with the previously deposited layer. This work proposes a process to print multilayers from the same solvent system utilizing the aerosol‐jet technique. By fine adjustment of the aerosol properties through the tube temperature (TTube), the drying time of poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) printed layers is significantly reduced. This allows its deposition onto a P3HT‐based bulk‐heterojunction (BHJ) without negatively affecting its performance. The additional printed P3HT layer, spatially extends the donor region of the BHJ, providing ideal hole extraction and simultaneous noise reduction by the blocking of injected electrons. This donor blocking layer (DBL) yields a noise reduction of two orders of magnitude in OPDs operated under −2 V reverse bias.

Inkjet-Printed Tin Oxide Hole-Blocking Layers for Organic Photodiodes

“…Current–voltage measurements in the dark with a 50 mV step size were performed with an Agilent 4155C. For the determination of SR (or external quantum efficiency, EQE), bandwidth, and S n , the same home-built measurement setup as described in refs , , and was used. In this setup, current or voltage measurements and bias settings were performed with a source meter unit (SMU, Keithley 2636A).…”

“…State-of-the-art OPDs already offer responsivities of >0.5 A W –1 , which are comparable to those of their silicon counterparts. ,− However, high dark currents and electrical noise under reverse bias are still the main limiting factors to improve their sensitivity and signal-to-noise ratio. − There are different approaches to minimize undesired carrier injection ranging from changes in the active layer such as enhanced absorber layer thickness or reduced energetic disorder , to the careful selection of electrodes or interlayer materials. − Particularly in OPDs, interlayers with appropriate energy levels have proven to be effective to reduce the parasitic charge injection from the electrodes into the HOMO or LUMO levels of the donor or acceptor constituents. − OPDs with dark current densities as low as 10 –1 to 10 –2 nA cm –2 and specific detectivities above 10 13 Jones have recently been reported. ,,, …”

Recent Advances in Solution‐Processable Organic Photodetectors and Applications in Flexible Electronics

“…Intense research efforts have been made to find the charge blocking materials for making low-noise OPDs. [26,[42][43][44][45] Recently, the solution-processed CuSCN was used as the electron blocking layer in the NT40:IEICO-4F-based broadband OPDs, showing a significant function of blocking the electron injection in the OPDs. [46] The CuSCN interlayer was found to form a higher electron-injection barrier between the anode and organic photoactive layer, creating a higher shunt resistance in OPDs compared to that of the OPDs with a PEDOT:PSS interlayer due to its higher conduction band in CuSCN (Figure 3e).…”

“…[ 124 ] The aerosol jet printing technique was used to deposit the electron blocking layers on the top of the organic photoactive layer in OPDs without requiring orthogonal solvents or cross‐linking treatment of the underlayer. [ 44 ] Fully printed nonfullerene acceptors (NFAs)‐based OPDs were demonstrated by inkjet‐printing the ZnO and organic photoactive layer, and aerosol‐jet‐printing the conductive PEDOT:PSS electrode. The digitally printed OPDs have achieved excellent responsivities up to 300 mA W −1 in the visible and NIR spectrum.…”

Carrier Blocking Layer Materials and Application in Organic Photodetectors

“…The aerosol-jet technique is another process to print multilayers from the same solvent system. Hernandez-Sosa and co-authors allowed deposition onto a P3HT-based BHJ without negatively affecting OPD performance [135]. This donor EBL yielded a noise reduction of two orders of magnitude in OPDs operated under −2 V bias.…”