Improving the Stability of Non-fullerene-Based Organic Photovoltaics through Sequential Deposition and Utilization of a Quasi-orthogonal Solvent.

The development of organic photovoltaic (OPV) devices based on non-fullerene acceptors (NFAs) has led to a rapid improvement in their efficiency. Despite these improvements, significant performance degradation in the early stages of operation, known as burn-in, remains a challenge for NFA-based OPVs. To address this challenge, this study demonstrates a stable NFA-based OPV fabricated using sequential deposition (SqD) and a quasi-orthogonal solvent. The quasi-orthogonal solvent, which is prepared by incorporating 1-chloronaphthalene (1-CN) into dichloromethane (DCM), reduces the vapor pressure of the solvent and allows for the efficient dissolution and penetration of the Y6 (one of efficient NFAs) into a PM6 polymer-donor layer without damaging the latter. The resulting bulk heterojunction (BHJ) is characterized by a higher degree of crystallinity in the PM6 domains than that prepared using a conventional single-step deposition (SD) process. The OPV fabricated using the SqD process exhibits a PCE of 14.1% and demonstrates superior thermal stability to the SD-processed OPV. This study conclusively reveals that the formation of a thermally stable interface between the photoactive layer and the electron-transport layer (ETL) is the primary factor contributing to the high thermal stability observed in the SqD-processed OPV.

Energy recycling under ambient illumination for internet-of-things using metal/oxide/metal-based colorful organic photovoltaics.

Colorful indoor organic photovoltaics (OPVs) have attracted considerable attention in recent years for their autonomous function in internet-of-things (IoT) devices. In this study, a solution-processed TiO2layer in a metal-oxide-metal (MOM) color filter electrode is used for light energy recycling in P3HT:ICBA-based indoor OPVs. The MOM electrode allows for tuning of the optical cavity mode to maximize photocurrent production by modulating the thickness of the TiO2layer in the sandwich structure. This approach preserves the OPVs' optoelectronic properties without damaging the photoactive layer and enables them to display a suitable range of vivid colors. The optimized MOM-OPVs demonstrated an excellent power conversion efficiency (PCE) of 8.8% ± 0.2%, which is approximately 20% higher than that of reference opaque OPVs under 1000 lx light emitting diode illumination. This can be attributed to the high photocurrent density due to the nonresonant light reflected from metals into the photoactive layer. Additionally, the proposed MOM-OPVs exhibited high external quantum efficiency and large parasitic shunt resistances, leading to improved fill factor and PCE values. Thus, the study's MOM electrode provides excellent feasibility for realizing colorful and efficient indoor OPVs for IoT applications.

Panchromatically Responsive Organic Photodiodes utilizing a Noninvasive Narrowband Color Electrode.

Organic photodiodes (OPDs) are emerging as potential candidates in image sensors owing to their high sensitivity and submicron photoactive layer thickness. For OPDs to be more competitive, it is necessary to develop an economical fabrication process and improve their narrowband spectral response from visible to near-infrared (NIR). In this study, panchromatic OPDs with a remarkable narrowband response from visible to NIR are developed by integrating a solution-processed optical filter-electrode (OF-electrode) and a panchromatic organic photoactive layer. Solution-processable TiO2 nanoparticles (sTNPs) bound to an acetylacetone ligand are used to construct the OF-electrode, which had the structure Ag/sTNP/Ag, and a ternary blend of a polymer donor, a nonfullerene acceptor, and a fullerene acceptor is used for preparing the panchromatic organic photoactive layer. Direct integration of the OF-electrode with the organic photoactive layer eliminates the need for additional OF installation, without damaging the underlying organic photoactive layer. Variation of the sTNP layer thickness controls the color filtering wavelength to vary from visible to NIR, with exceptionally narrow full width at half-maximum (fwhm) values of 48-82 nm and transparency values of 50-70%. Owing to their selective response for the desired color and their capability to minimize noise from other colors, the OPDs exhibit high sensitivity values of 2.82 × 1012, 3.02 × 1012, and 3.94 × 1012 cm Hz0.5/W (Jones) with narrow fwhm values of 110, 91, and 75 nm at a peak transmittance exceeding 65% for blue, green, and red, respectively. Furthermore, they detect NIR light at a wavelength of 950 nm with a narrow fwhm value of 51 nm and a high sensitivity of 3.78 × 1012 cm Hz0.5/W (Jones).

Active-Material-Independent Color-Tunable Semitransparent Organic Solar Cells.

Semitransparent colorful organic solar cells (OSC) provide exciting opportunities for harnessing sunlight as colored windows. Previously, color filter (CF) electrodes on (OSC) were demonstrated via vacuum-deposition techniques, resulting in deposition-induced damage. Thus, we present CF integrated organic photovoltaics (CF-OPVs) using solution-processed TiO2-AcAc as the dielectric component. The noninvasive processing substantially expands the range of usable active materials, allowing the device to display pure and vibrant colors that are independent of the inherent color of the active material and show superior optical and photovoltaic characteristics. These results provide practical pathways to realizing colored semitransparent solar cells.

Thermally Stable Bulk Heterojunction Prepared by Sequential Deposition of Nanostructured Polymer and Fullerene.

A morphologically-stable polymer/fullerene heterojunction has been prepared by minimizing the intermixing between polymer and fullerene via sequential deposition (SqD) of a polymer and a fullerene solution. A low crystalline conjugated polymer of PCPDTBT (poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta [2,1-b;3,4-b']dithiophene)-alt-4,7(2,1,3-benzothiadiazole)]) has been utilized for the polymer layer and PC71BM (phenyl-C71-butyric-acid-methyl ester) for the fullerene layer, respectively. Firstly, a nanostructured PCPDTBT bottom layer was developed by utilizing various additives to increase the surface area of the polymer film. The PC71BM solution was prepared by dissolving it in the 1,2-dichloroethane (DCE), exhibiting a lower vapor pressure and slower diffusion into the polymer layer. The deposition of the PC71BM solution on the nanostructured PCPDTBT layer forms an inter-digitated bulk heterojunction (ID-BHJ) with minimized intermixing. The organic photovoltaic (OPV) device utilizing the ID-BHJ photoactive layer exhibits a highly reproducible solar cell performance. In spite of restricted intermixing between the PC71BM and the PCPDTBT, the efficiency of ID-BHJ OPVs (3.36%) is comparable to that of OPVs (3.87%) prepared by the conventional method (deposition of a blended solution of polymer:fullerene). The thermal stability of the ID-BHJ is superior to the bulk heterojunction (BHJ) prepared by the conventional method. The ID-BHJ OPV maintains 70% of its initial efficiency after thermal stress application for twelve days at 80 °C, whereas the conventional BHJ OPV maintains only 40% of its initial efficiency.

Near infrared organic photodetector utilizing a double electron blocking layer.

A near infrared organic photodiode (OPD) utilizing a double electron blocking layer (EBL) fabricated by the sequential deposition of molybdenum (VI) oxide (MoO3) and poly(3,4ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) is reported. The double EBL improves the on/off current ratio of OPD up to 1.36 x 104 at -1V, which is one order of magnitude higher than PEDOT:PSS single EBL (2.45 x 103) and three orders of magnitude higher than that of MoO3 single EBL (7.86). The detectivity at near infrared (800 nm) at -1V is 4.90 x 1011 Jones, which is 2.83 times higher than the PEDOT:PSS single EBL and 2 magnitudes higher compared to the MoO3 single EBL.

Solution processed organic photodetector utilizing an interdiffused polymer/fullerene bilayer.

Low dark current (off-current) and high photo current are both essential for a solution processed organic photodetector (OPD) to achieve high photo-responsivity. Currently, most OPDs utilize a bulk heterojunction (BHJ) photo-active layer that is prepared by the one-step deposition of a polymer:fullerene blend solution. However, the BHJ structure is the main cause of the high dark current in solution processed OPDs. It is revealed that the detectivity and spectral responsivity of the OPD can be improved by utilizing a photo-active layer consisting of an interdiffused polymer/fullerene bilayer (ID-BL). This ID-BL is prepared by the sequential solution deposition (SqD) of poly(3-hexylthiophene) (P3HT) and [6,6] phenyl C61 butyric acid methyl ester (PCBM) solutions. The ID-BL OPD is found to prevent undesirable electron injection from the hole-collecting electrode to the ID-BL photo-active layer resulting in a reduced dark current in the ID-BL OPD. Based on dark current and external quantum efficiency (EQE) analysis, the detectivity of the ID-BL OPD is determined to be 7.60 × 10(11) Jones at 620 nm. This value is 3.4 times higher than that of BHJ OPDs. Furthermore, compared to BHJ OPDs, the ID-BL OPD exhibited a more consistent spectral response in the range of 400 - 660 nm.