Thickness Of Photoactive Layer Research Articles

Precise control of hole transport layer integration on PDTS-DTTFBT: PC71BM organic solar cells

Efforts to enhance the commercial viability of organic solar cells (OSCs) prioritize high power conversion efficiency(PCE). This study proposes precision tuning of the photoactive layer thickness in the nanoscale as an innovative method to boost efficiency. Utilizing PDTS-DTTFBT: PC71BM, an organic blend, as the active layer aims to capture a broad photon range while addressing optical losses due to low-energy photons rather than mere absorption. The study integrates PEDOT: PSS and molybdenum trioxide (MoO3) as hole transport layers, alongside C60, PC60BM, and ZnO electron transport layers. Meticulous analysis of their photon absorption, reflectance, charge carrier generation, and localized energy variance emphasizes their impact on the efficiency of PDTS-DTFFBT: PC71BM active films. Notably, incorporating MoO3 as the hole transport layer significantly mitigated losses and altered localized energy, culminating in an impressive 17.69% efficiency at an optimized blend thickness of 120 nm. Augmenting blend thickness directly boosts PCE and current density until reaching optimal thickness, while diminishing fill factor, with minimal effect on open-circuit voltage. These results highlight the efficacy of this methodology in enhancing the performance of organic solar cells.

Asymmetric Non-Fullerene Acceptor Derivatives Incorporated Ternary Organic Solar Cells.

Incorporating ITIC derivatives as guest acceptors into binary host systems is an effective strategy for constructing high-performance ternary organic solar cells (TOSCs). In this work, we introduced A-D-A type ITIC derivatives PTBTT-4F (asymmetric) and PTBTP-4F (symmetric) into the PM6:BTP-BO-4F (Y6-BO) binary blend and investigated the impacts of two guest acceptors on the performance of TOSCs. Differentiated device performance was observed, although PTBTT-4F and PTBTP-4F presented similar chemical structures and comparable absorptions. The PTBTT-4F ternary devices exhibited an improved power conversion efficiency (PCE) of 17.67% with increased open circuit (VOC) and current density (JSC), whereas the PTBTP-4F-based ternary devices yielded a relatively lower PCE of 16.34%. PTBTT-4F showed much better compatibility with the host acceptor BTP-BO-4F, so that they formed a well-mixed alloy phase state; more precise phase separation and increased crystallinity were thus induced in the ternary blends, leading to reduced molecular recombination and improved charge mobilities, which contributed to improved fill factors of the ternary devices. In addition, the optimized PTBTT-4F devices exhibited good performance tolerance of the photoactive layer thickness, as they even delivered a PCE of 15.25% when the active layer was as thick as up to ∼300 nm.

The impact of plasmonic electrodes on the photocarrier extraction of inverted organic bulk heterojunction solar cells

Nano-patterning the semiconducting photoactive layer/back electrode interface of organic photovoltaic devices is a widely accepted approach to enhance the power conversion efficiency through the exploitation of numerous photonic and plasmonic effects. Yet, nano-patterning the semiconductor/metal interface leads to intertwined effects that impact the optical as well as the electrical characteristic of solar cells. In this work we aim to disentangle the optical and electrical effects of a nano-structured semiconductor/metal interface on the device performance. For this, we use an inverted bulk heterojunction P3HT:PCBM solar cell structure, where the nano-patterned photoactive layer/back electrode interface is realized by patterning the active layer with sinusoidal grating profiles bearing a periodicity of 300 nm or 400 nm through imprint lithography while varying the photoactive layer thickness (LPAL) between 90 and 400 nm. The optical and electrical device characteristics of nano-patterned solar cells are compared to the characteristics of control devices, featuring a planar photoactive layer/back electrode interface. We find that patterned solar cells show for an enhanced photocurrent generation for a LPAL above 284 nm, which is not observed when using thinner active layer thicknesses. Simulating the optical characteristic of planar and patterned devices through a finite-difference time-domain approach proves for an increased light absorption in presence of a patterned electrode interface, originating from the excitation of propagating surface plasmon and dielectric waveguide modes. Evaluation of the external quantum efficiency characteristic and the voltage dependent charge extraction characteristics of fabricated planar and patterned solar cells reveals, however, that the increased photocurrents of patterned devices do not stem from an optical enhancement but from an improved charge carrier extraction efficiency in the space charge limited extraction regime. Presented findings clearly demonstrate that the improved charge extraction efficiency of patterned solar cells is linked to the periodic surface corrugation of the (back) electrode interface.

High‐Performance Green Thick‐Film Ternary Organic Solar Cells Enabled by Crystallinity Regulation

AbstractThe power conversion efficiency (PCE) of organic solar cells (OSCs) has reached high values of over 19%. However, most of the high‐efficiency OSCs are fabricated by spin‐coating with toxic solvents and the optimal photoactive layer thickness is limited to 100 nm, limiting practical development of OSCs. It is a great challenge to obtain ideal morphology for high‐efficiency thick‐film OSCs when using non‐halogenated solvents due to the unfavorable film formation kinetics. Herein, high‐efficiency ternary thick‐film (300 nm) OSCs with PCE of 15.4% based on PM6:BTR‐Cl:CH1007 are fabricated by hot slot‐die coating using non‐halogenated solvent (o‐xylene) in the air. Compared to PM6:BTR‐Cl:Y6 blends, the stronger pre‐aggregation of CH1007 in solution induces the earlier aggregation of CH1007 molecules and longer aggregation time, and thus results in high and balanced crystallinity of donors and acceptor in CH1007‐based ternary film, which led to high‐carrier mobility and suppressed charge recombination. The ternary strategy is further used to fabricate high‐efficiency, thick‐film, large‐area, and flexible devices processed from non‐halogenated solvents, paving the way for industrial development of OSCs.

Synthesis, characterizations and photovoltaic applications of a thickness-insensitive benzodifuran based copolymer

Low toleration of thickness variations in the organic solar cells (OSCs), is currently becoming bottleneck challenges to achieve power conversion efficiencies (PCE) and large-scaled roll-to-roll device fabrication. In this work, a new thienyl-free furan-based copolymer of PBDFDFBO was synthesized via Stille copolymerization of benzodifuran (BDF) and 4,7-di(furan-2-yl)benzo[c][1,2,5]oxadiazole monomers. It exhibited a high hole mobility of 2.46 × 10−3 cm2 V−1 S−1, which could be attributed to a planar molecular conformation of the polymer. When the polymer was selected as donor and small molecular ITIC-F as acceptor, the photovoltaic device results showed a champion PCE of 11.53% with a high Voc and FF. Impressively, device efficiency is insensitive to the variation of photoactive layer thickness and can maintain over 10.98% efficiency as film thickness increases to 600 nm, which is the best result for furan-based OSCs. The features of all furan-based polymer of PBDFDFBO provide great potential in developing thick film photovoltaic device and the efficient molecular design strategy also could be referenced to other photovoltaic materials.

16.52% Efficiency All-Polymer Solar Cells with High Tolerance of the Photoactive Layer Thickness.

All-polymer solar cells (all-PSCs) have drawn growing attention and achieved tremendous progress recently, but their power conversion efficiency (PCE) still lags behind small-molecule-acceptor (SMA)-based PSCs due to the relative difficulty on morphology control of polymer photoactive blends. Here, low-cost PTQ10 is introduced as a second polymer donor (a third component) into the PM6:PY-IT blend to finely tune the energy-level matching and microscopic morphology of the polymer blend photoactive layer. The addition of PTQ10 decreases the π-π stacking distance, and increases the π-π stacking coherence length and the ordered face-on molecular packing orientation, which improves the charge separation and transport in the photoactive layer. Moreover, the deeper highest occupied molecular orbital energy level of the PTQ10 polymer donor than PM6 leads to higher open-circuit voltage of the ternary all-PSCs. As a result, a PCE of 16.52% is achieved for ternary all-PSCs, which is one of the highest PCEs for all-PSCs. In addition, the ternary devices exhibit a high tolerance of the photoactive layer thickness with high PCEs of 15.27% and 13.91% at photoactive layer thickness of ≈205 and ≈306nm, respectively, which are the highest PCEs so far for all-PSCs with a thick photoactive layer.

High-performance ternary organic photovoltaics with NC70BA as the third component material enabling thickness-insensitive photoactive performance

In this work, a thinner (100 nm) and thicker (150 and 200 nm) ternary organic photovoltaic (OPV) are fabricate by D18 as donor, Y6 as acceptor and NC70BA as third component materials. The addition of the hollow 3D spherical structure of NC70BA into D18:Y6 binary films is helpful for improving phase separation and smooth surface of ternary photoactive layer, and form more continuous electron transport channels in ternary photoactive layers. It is enhance photovoltaic performance under not only thinner photoactive layer thickness but also thicker photoactive layer thickness. Our results demonstrate the feasibility of employing D18:Y6 as a binary photovoltaic layer and fullerene derivative NC70BA as a third component material and has construct high-efficiency thickness-insensitive ternary OPVs; this approach would promote the development of thicker photoactive layer ternary OPVs to fulfill the requirements of solution coating processes.

Optoelectronic performance characterization of MoS2 photodetectors for low frequency sensing applications

The specific advantages of implementing MoS2 and other layered semiconductors for optoelectronic biosensing and other relevant photodetection applications remain unclear. In this work, we investigate the photoresponsivity and noise characteristics of in-plane MoS2 photodetectors. This work indicates that MoS2 photodetectors exhibit lower noise equivalent power (NEP) and detectivity (D*) in comparison with commercial CdS photodetectors. In addition, the low-frequency NEP and D* values of MoS2 photodetectors exhibit a prominent dependence on the MoS2 photoactive layer thickness. We have identified the optimal MoS2 thickness in the range of 8–30 nm. We also study the photoresponse characteristics of optimized MoS2 photodetectors at several different wavelengths that are important for clinical colorimetry assays. Such an optimized photodetector shows a maximum photoresponsivity of 164.3 A/W and a minimum NEP of 3.99 × 10−17 W/Hz1/2 (and a D* of 5.01 × 1010 J) with relative variance less than 14%. This work provides a useful guideline for optimizing the photoresponse characteristics of MoS2-based optoelectronic devices, which is critical to practical low-frequency optoelectronic biosensing applications.

Investigating the Indoor Performance of Planar Heterojunction Based Organic Photovoltaics

Recently, the bulk heterojunction (BHJ)-based photoactive layer has been favored over the planar heterojunction (PHJ)-based photoactive layer for organic photovoltaics (OPVs), owing to the evitable thickness limit of the latter induced by the low mobility of charge carriers. However, under dim indoor light conditions, the PV performance becomes immune to the resistive components of the PHJ OPVs, such as a thick photoactive layer, thereby rendering them attractive for operating indoors. In this study, we devise and demonstrate indoor OPVs with a PHJ-based photoactive layer constituting poly(3-hexylthiophene-2,5-diyl) (P3HT) and indene-C60 bisadduct (ICBA). The performance of the PHJ OPVs was optimized by modulating the thickness of the ICBA layer under a 1000 lx light-emitting diode lamp. OPVs with a 65 nm-thick ICBA layer exhibited excellent indoor performance with a power conversion efficiency of 15.3 ± 0.3%, comparable to that of the reference BHJ OPVs (15.0 ± 0.2%). No noticeable performance degradation was observed by increasing the thickness of the PHJ-based photoactive layer; instead, a thick photoactive layer only enhanced the light absorption, resulting in excellent indoor performance with a higher photocurrent.

A common optical approach to thickness optimization in polymer and perovskite solar cells

The structure of experimentally designed solar cells was optimized in terms of the photoactive layer thickness for both organic bulk heterojunction and hybrid perovskite solar cells. The photoactive layer thickness had a totally different behavior on the performance of the organic and hybrid solar cells. Analysis of the optical parameters using transfer matrix modeling within the Maxwell–Garnett effective refractive index model shows that light absorbance and exciton generation rate in the photoactive layer can be used to optimize the thickness range of the photoactive layer. Complete agreement between experimental and simulated data for solar cells with photoactive materials that have very different natures proves the validity of the proposed modeling method. The proposed simple method which is not time-consuming to implement permits to obtain a preliminary assessment of the reasonable range of layer thickness that will be needed for designing experimental samples.

Indoor Organic Photovoltaics: Optimal Cell Design Principles with Synergistic Parasitic Resistance and Optical Modulation Effect

AbstractRecently, indoor organic photovoltaics (OPVs) has attracted substantial research attention, due to the emergence of self‐powered electronic devices for Internet‐of‐Things (IoT) applications. This progress report discusses recent developments in indoor OPVs, focusing on the strategic role of synergistic parasitic resistance in suppressing the leakage current to achieve high indoor efficiencies. Moreover, an underexplored area is presented, namely the impact of optical modulation on enhancing light absorption in indoor OPVs. First, the main advances in material design for indoor OPVs are briefly presented. This is followed by detailed discussions of the crucial strategies, including interfacial engineering, the effect of photoactive layer thickness, and the effectiveness of transparent conducting electrodes for improving the OPV performance. Overall, this review highlights that understanding the indispensable role of parasitic resistance under dim light conditions may provide new opportunities for developing efficient indoor OPVs for practical applications. Finally, after summarizing recent progress in indoor OPVs, a critical perspective is provided.

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).

Enhancement of power conversion efficiency of dye-sensitized solar cells for indoor applications by using a highly responsive organic dye and tailoring the thickness of photoactive layer

Dye-sensitized solar cells (DSSCs) based on different configurations under various light intensity are characterized, where commercial N719 dye and synthesized D-Dye are used as photo-sensitizer. Regardless of cell configuration, organic D-Dye serves as an efficient photo-sensitizer, giving rise to high cell efficiency comparable with N719. The highest efficiency of 20.98% (Voc of 0.6 V, Jsc of 0.62 mA/cm2, FF of 0.71) is achieved as the front-illuminated rigid DSSC is constructed by applying 8 μm TiO2 layer under 6000 LUX illumination. At the same condition the efficiency of 19.69% (Voc of 0.63 V, Jsc of 0.57 mA/cm2, FF of 0.74) is recorded for N719. Higher efficiency for D-Dye is attributed to high response of its absorption spectrum to the emission spectrum of indoor T5 irradiance. Charge transfer resistance is measured to be 53.1 Ω for D-Dye in conjunction with 8 μm TiO2 which is higher than thicker TiO2 (10 μm and 12 μm) at 0.75 V applied bias under dark condition, indicating that reduction of TiO2 thickness facilitates charge transfer by suppressing charge recombination under low illuminations. A systematic study of the efficiency as a function of key factors like TiO2 thickness, electrode type, and light intensity is explored.

Inverted bulk heterojunction organic solar cells using optimization of active layer deposition via controlling of doctor blade parameters

The thickness of photoactive layer is important parameter to harness the maximum amount of sunlight and to achieve high power conversion efficiency (PCE) in polymer solar cells (PSCs). In order to harvest more energy, the solar radiation requires to be sufficiently absorbed in the active layer and the charge carriers should be efficiently collected. The main focus of this present literature is preparation of P3HT: PCBM (poly (3-hexylthiophene), [6.6]-phenyl-C60-butyric acid methyl ester) blend acting as an active layer by using the Doctor Blade coating (DBC) at various speeds (15, 20, 25 and 30 mm/s). The Doctor Blade coating is a useful technique for large-scale, fast and low-cost fabrication of solution-processed solar cells and it is widely used for device fabrication. By optimizing the thickness of the active layer, an improved efficiency of 3.44% with a high fill factor (FF) beyond 60% achieved. Controlling the active layer growth rate resulted in higher electron mobility and balanced charge transport.

14.4% efficiency all-polymer solar cell with broad absorption and low energy loss enabled by a novel polymer acceptor

Abstract All-polymer solar cells (All-PSCs) offer several distinct merits including superior thermal stability and flexibility. Here, we report a novel polymer acceptor PJ1 that exhibits a narrow band gap around 1.4 eV and a high extinction coefficient about 1.39 × 105 cm−1. When PJ1 is blended with donor polymer PBDB-T, all-PSC with a record power conversion efficiency (PCE) of 14.4% is achieved, which is mainly attributed to the broad absorption, efficient charge separation and collection, and low energy loss. The synergetic effects of molecular weight of PJ1 on the photovoltaic performance are also investigated. It is found that the increase in molecular weight can result in the red-shift of absorption along with slight enhancement of extinction coefficient, which therefore benefits photocurrent. In addition, all-PSC based on PJ1 demonstrate much better thermal stability than the control device based on small molecule acceptor (TTPBT-IC), as evidenced by the insignificant morphology change of PBDB-T:PJ1 versus excessive phase separation of PBDB-T:TTPBT-IC when annealed at 150 °C. Of particular interest is that the all-PSCs based on PBDB-T:PJ1 can retain high PCEs even when the thickness of photoactive layer is increased over 300 nm (PCE of 12.1%) or the device area is enlarged to 1 cm2 (PCE of 13.0%).

Light-intensity and thickness dependent efficiency of planar perovskite solar cells: charge recombinationversusextraction

We reveal the complex interplay between photoactive layer thickness and illumination intensity in perovskite solar cells, presenting design criteria for real-world and solar concentrator applications.

Tail state limited photocurrent collection of thick photoactive layers in organic solar cells

We analyse organic solar cells with four different photoactive blends exhibiting differing dependencies of short-circuit current upon photoactive layer thickness. These blends and devices are analysed by transient optoelectronic techniques of carrier kinetics and densities, air photoemission spectroscopy of material energetics, Kelvin probe measurements of work function, Mott-Schottky analyses of apparent doping density and by device modelling. We conclude that, for the device series studied, the photocurrent loss with thick active layers is primarily associated with the accumulation of photo-generated charge carriers in intra-bandgap tail states. This charge accumulation screens the device internal electrical field, preventing efficient charge collection. Purification of one studied donor polymer is observed to reduce tail state distribution and density and increase the maximal photoactive thickness for efficient operation. Our work suggests that selecting organic photoactive layers with a narrow distribution of tail states is a key requirement for the fabrication of efficient, high photocurrent, thick organic solar cells.

A novel approach for preparation of CH3NH3PbBr3 via direct transformation of electrodeposited PbO2 for photodetector application

Organic–inorganic hybrid perovskites are crystals with efficient light absorption, high charge carrier mobility and long electron/hole diffusion path that have been developed to enhance sunlight energy application. In particular, lead-based compounds by establishing excellent performance in 3rd generation solar cells led to an increased interest in testing them in other areas such as photodetectors, diodes, and transistors. Herein, we report a simple, scalable and versatile fabrication process of CH3NH3PbBr3 layer through electrodeposition technique without using a glove box or a high vacuum system. Measurements demonstrated that a high quality crystalline structure in a pinhole free perovskite layer was obtained. The fabricated photodetector devices made of electrodeposited MAPbBr3 films displayed significant performance with the on/off current ratio of 3 × 106 under white light radiation at 0.1 V bias voltage. Increasing the thickness of photoactive absorber layer up to 1 µm led to 7% external quantum efficiency and 34.4% improvement of EQE compared to 546 nm film.

Inkjet printed organic detectors with flat responsivity up to the NIR and inherent UV optical filtering

Abstract The use of printing technologies is widely recognized to be a major advantage for the deployment of large-area organic electronics and there is still plenty of room for exploring new strategies to exploit printing of solution processable conductors and semiconductors. In this paper, we show for the first time how an additive layer-by-layer deposition, achieved through inkjet printing, enables the fabrication of broadband organic photodetectors with a flat responsivity spectrum extending to the near-infrared (NIR). The use of narrow bandgap polymers enables light detection up to 1.1 μm. By controlling the photoactive layer thickness in a range between 150 nm and 4 μm, we could filter the contribution from UV and Vis absorption to the photocurrent, while keeping light detection in the NIR. The visible detection efficiency decreases of a 70% at 425 nm for thicknesses going from 250 nm up to 2 μm, while the NIR detection decreases only of 31% at 950 nm, and increases of 26% at 1020 nm. This photoactive layer thickness dependent UV–vis optical filtering enables the control over the shape of the responsivity spectra.

High-Performance All-Polymer Photodetectors via a Thick Photoactive Layer Strategy.

To achieve high detectivity in all-polymer photodetectors (all-PPDs), a thick-film photoactive layer is favored because it can effectively suppress the dark current density. However, if the photoactive layer of the film is too thick, it leads to reduced responsivity owing to increased recombination loss. We developed high-performance all-PPDs by using a narrowband-gap p-type polymer NT40 and an n-type polymer poly{[ N, N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]- alt-5,5'-(2,2'bithiophene)} as the photoactive layer. The high charge carrier mobility of both copolymers enabled a photoactive layer thickness of 300 nm, leading to an ultralow dark current density of 4.85 × 10-10 A cm-2, a detectivity of 2.61 × 1013 Jones, a high responsivity of 0.33 A W-1 at 720 nm, and a bias of -0.1 V. The detectivity achieved >1013 Jones in a wide range from 360 to 850 nm, which is among the highest values so far reported for all-PPDs without extra gains. More importantly, the resultant all-PPDs exhibited a high working frequency over 10 kHz associated with a large linear dynamic range. These findings demonstrate great potential for practical applications of the all-PPDs developed in this work.