Facile Tuning the Detection Spectrum of Organic Thin Film Photodiode via Selective Exciton Activation

Here, we introduce a method of tuning the high-detectivity spectra of the organic photodiode (OPD) to fabricate a thin-film filter-less full-color image sensor. The strategically introduced PIN junction enables a selective activation of excitons generated from the photons with low extinction coefficient in the active layer such that the separated holes/electrons can contribute to the external current. In addition, we show that a well-defined PIN junction blocks the injection of nonallowed charge carriers, leading to very low dark current and near-ideal diode characteristics. Consequently, the high specific detectivity over 1.0 × 10¹² Jones are observed from R/G/B-selective thin-film OPDs

Fabrication of High Performance, Narrowband Blue-Selective Polymer Photodiodes with Dialkoxynaphthalene-Based Conjugated Polymer

Here, we synthesized a dihexyloxynaphthalene-based conjugated polymer (PNa6-Th) to realize narrowband blue-selective polymer photodiode. The optical, electrochemical, and thermal properties of the synthesized polymer were investigated. It was found that PNa6-Th exhibited a blue-selective absorption with a narrow full width at half-maximum of ∼100 nm and a wide optical band gap of ∼2.52 eV. We constructed a planar heterojunction structure with PNa6-Th and ZnO as a blue-selective electron donor and nonabsorbing acceptor, respectively; To enhance the photodiode performance, a minor amount of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) was introduced on the donor layer. By introducing the PCBM on PNa6-Th layer, external quantum efficiency was increased from 5.4% for pristine device to 37.8% for 15 wt % PCBM-doped device, while the dark current values maintained nearly constant. This external quantum efficiency boost leads to high detectivity of 2.31 × 10¹² Jones at −1 V. The physics behind the improved performance were fully discussed based on percolation pathway theory and space-charge-limited current analyses

Development of Novel Conjugated Polyelectrolytes as Water-Processable Interlayer Materials for High-Performance Organic Photodiodes

A series of novel conjugated polyelectrolytes composed of two different building blocks with different composition ratios were designed and synthesized for application as a functional layer in high-performance organic photodiodes (OPDs). A homopolymer and two random copolymers were prepared using different molar ratios of dibromo 1,4-bis­(4-sulfonatobutoxy)­benzene (SPh) and dibromo 1,4-bis­(4-tetraethylene glycol)­benzene (EGPh): <b>EG20</b> with SPh:EGPh ratio of 0.8:0.2 and <b>EG40</b> with a ratio of 0.6:0.4. Structural analyses by two-dimensional grazing-incidence X-ray diffraction and near-edge X-ray absorption fine structure spectroscopy studies proved that a higher EGPh content could induce more organized polymer chains with face-on orientation of <b>EG20</b> and <b>EG40</b>. Such an orientation of <b>EG20</b> and <b>EG40</b> along with the ordered crystalline organization yielded effective molecular dipole moments in the thin films when applied as an interlayer between ZnO and an active layer of inverted OPDs. As confirmed by ultraviolet photoelectron spectroscopy, the increase in EG content gradually shifted the workfunction of the ZnO, facilitating the inverted OPD to simultaneously achieve a decrease in dark current and enhancement in photocurrent. The synergetic effects introduced by the newly designed <b>EG20</b> and <b>EG40</b> resulted in significantly improved OPD performances with high specific detectivity up to 2.1 × 10¹³ Jones, 3 dB bandwidth of 72 kHz, and linear dynamic range of 110 dB