Butyric Acid Methyl Ester Blend Research Articles

Effect of Anode Interfacial Modification by Self-Assembled Monolayers on the Organic Solar Cell Performance.

A series of self-assembled monolayer (SAM)-based benzoic acid derivatives such as 4-[5'-phenyl-2,2'-bitien-5-yl] benzoic acid (ZE-Ph), 4-[5'-(4-fluorophenyl)-2,2'-bitien-5-yl]benzoic acid (ZE-1F), and 4-[5'-(3,5-difluorophenyl)-2,2'-bitien-5-yl]benzoic acid (ZE-2F) were synthesized to use an interlayer between an ITO electrode and a MoO3 thin film layer in an organic solar cell (OSC) having poly-3 hexylthiophene (P3HT): [6,6]-phenyl C61 butyric acid methyl ester (PC61BM) blend. The work function and surface wetting properties of the ITO were tuned by SAM molecules. The power conversion efficiency of fabricated OSC devices was improved compared to that of the control device from 1.93 to 2.20% and 2.22% with ZE-Ph and ZE-1F-modified ITO electrodes, respectively. The short-circuit current density (Jsc) was increased from 6.16 to 7.10 mA/cm2 and 6.94 mA/cm2 with control, ZE-Ph, and ZE-1F-modified solar cells, respectively. The increase in short-circuit current density (Jsc) shows that the hole-transporting properties between ITO and MoO3 were improved by the use of ZE-Ph and ZE-1F compared with that of the ITO/MoO3 electrode configuration. The open-circuit voltage (Voc) of the SAM-modified ITO-based devices was also improved compared with the Voc of unmodified ITO-based devices. These results show that using a monolayer as an interlayer in OSCs is an important strategy to improve the performance of OSCs. All the device parameters were characterized by Kelvin probe force microscopy, cyclic voltammetry, contact angle, and I-V measurements.

Semiconductor quantum dots as a mechanism to enhance charge transfer processes in polymer solar cells

The light trapping capability of thin film polymer solar absorber, composed of poly (3-hexylthiophene) and [6,6]–phenyl C61- butyric acid methyl ester (P3HT:PC60BM) blend, is improved using ZnS semiconductor quantum dots (QD) as third donor-acceptor (D:A) component. The inherent characteristics of the microwave-assisted synthesized ZnS QD, such as quantum size effect, and multiple exciton generation were leveraged in harvesting high energy photons, which resulted in a better exciton generation, dissociation, and effective charge transport in the polymer medium. The synthesized QD exhibited good phase purity, effective kinetic enhancement, and control of the aggregation process. Hence, the impact of ZnS QD on the performance of thin film polymer solar cells (TFPSC) is evident by a remarkable improvement in the measured photovoltaic parameters. Nonetheless, it is observed that the device performances are generally dependent on the concentration of the QD in the absorber layer. Consequently, the power conversion efficiency has increased by 58% at 3% concentration of QDs by weight. This is an interesting development of TFPSC fabricated under an ambient environment.

Effects of PCBM loading on high sensitive P3HT based vertical bulk resistive X-ray detector

Recently, semiconductive polymeric materials have attracted attention as an active layer for detecting ionizing radiation because of their excellent properties such as flexibility, easy production, solution processability and low-cost production. This paper presents X-ray detection properties of Poly(3-hexylthiophene) (P3HT):Phenyl C61 butyric acid methyl ester (PCBM) blend structure with different PCBM loading ratios. P3HT:PCBM mixing ratio was changed from 1:0 to 1:2. Top contact of the pure and blend structured device were produced by using a solution based graphite ink. Devices were constructed with vertical bulk resistive architecture within an ohmic electrode structure as ITO/PEDOT:PSS/P3HT:PCBM/Graphite configuration. Graphite electrode was coated on the active layer with the spray coating method. All devices exhibited ohmic current-voltage (I–V) characteristics. The blend structured devices exhibited stable saw-tooth type behaviour in photocurrent responses against the on and off states of X-rays. Saw-tooth type responses could be evaluated as major evidence for a potential usage of organic electronic device technology direct radiation detectors. Although the best sensitivity value to X-ray was obtained with the blend structure with equal ratio, it was observed that the rise and decay times were shortened with the increase in the amount of PCBM in the blend structure from. • P3HT:PCBM active layer based X Ray detectors were fabricated and effect of PCBM ratio was investigated. • Spray coated graphite electrode was used as the top ohmic contact for all devices. • P3HT:PCBM ratio was changed as (1:0), (1:0.5), (1:1), (1:2) and investigate PCBM concentrations how effect X Ray detection parameters with different X Ray dose rates under 10 V bias. • Best sensitivity value to X-ray was obtained with the blend structure with equal ratio of PCBM and P3HT (1:1).

Effective energy harvesting in thin film organic solar cells using Ni:Zn as bimetallic nanoparticles

This article explores the effect of bimetallic plasmonic nanocomposites in the solar absorber layers of thin-film organic solar cells (TFOSCs) for possible improvement in harvesting solar energy. To achieve this goal, a new nanocomposite composed of Nickel and Zinc (Ni: Zn) was successfully synthesized by the use of a chemical reduction processes. The effect of bimetallic nanocomposites was studied using a photoactive medium, which comprises of poly-(3-hexylthiophene) (P3HT) [6,6]-phenyl C61 butyric acid methyl ester (PC61BM) blend and doped with Ni:Zn at different concentrations. Consequently, an improved power conversion efficiency value up to 4.78% was found at 1% Ni:Zn bimetallic concentration by weight compared to reference solar cell. This is a clear indication of the influence of Ni:Zn bimetallic nanoparticles on the performance of TFOSC. These effects have been realized by the occurrence of local surface plasmon resonance (LSPR) phenomenon caused by Ni: Zn nanoparticles in polymer medium.

Modelling and Calculation of Characteristic Parameters of the Active and Buffer Layers in Organic Solar Cell

Background: The active layer not only must have a strong light absorption in the visible spectrum but must also be sufficient for charge carrier transport to the electrodes. Electrons in conducting polymer transport by hopping between different energy levels resulted in much lower charge mobility. Therefore, the thickness of the active layer must be limited, so the separated charge can reach the corresponding electrodes without recombination. However, a thin active layer has weaker light absorption, resulting in the low photogenerated current in organic solar cell devices. Furthermore, buffer layers usually have high charge mobility, which in turn would enhance the transportation of charge from the active layer to electrodes. Metal oxides have been studied to be used as a cathode buffer layer, such as titanium dioxide (TiO2), zinc oxide (ZnO), etc. Objective: In this work, behaviors of the photon-electrical characteristics with variation in thickness of the active (poly(3-hexylthiophene-2,5-diyl) and phenyl-C61 butyric acid methyl ester blend) and buffer (zinc oxide) layers were investigated. Methods: The influences of the thickness of the active and buffer layers on characteristic parameters of organic solar cells were investigated by solving the drift and diffusion equation with the photogenerated current given by the Hetch equation. Results: The optimum thickness was obtained around 100 nm and below 10 nm for the active and the ZnO buffer layers, respectively. Conclusion: Thinner active layer resulted in lower photocurrent due to poor light absorption while at 150 nm thick and above, PCE of the device reduced rapidly because of the high recombination rate of photogenerated electron-hole pairs. ZnO buffer layer was used as an electron transport layer and a hole blocking layer in order to improve the cell’s performance. The addition of ZnO enhanced the PCE up to 2.48 times higher than the conventional device.

Influence of Top Layer Composition on the Photovoltaic Parameters of P3HT:PCBM Organic Solar Cells

Spin and spray deposition techniques have been used sequentially to examine the effect of the composition of top blend layer on the photovoltaic properties of organic solar cells using well-known poly(3-hexylthiophene):[6,6]-Phenyl C61 butyric acid methyl ester (P3HT:PCBM) blend. Devices were prepared by spraying an extra layer of P3HT or PCBM (~15 nm) onto spin coated (1:1) blend film. P3HT-rich top phase slightly perturbs photovoltaic activity whereas PCBM-rich top phase drastically changes the power conversion efficiencies with a marked decrease in fill factors. Carrier mobilities were only marginally affected by the presence of spray coated top layers. However, series resistance of top phase P3HT-rich blends remained the same with respect to spin coated sample whereas top phase PCBM-rich blends exhibit relatively higher series resistances for both annealed and non-annealed samples. Based on the presented results, one might speculate that electron injection to cathode with P3HT is almost as efficient as with PCBM for active layers utilizing P3HT:PCBM blend.

Improved stability and performance of organic photovoltaic cells by application of carbon nanostructures and PEDOT:PSS composites as additional transparent electrodes

Conventional bulk heterojunction organic photovoltaic cell (OPVC) with regioregular poly[3-hexylthiophene-2,5-diyl] (P3HT): [6,6]-phenyl C61 butyric acid methyl ester (PCBM) blend as active layer has been fabricated with simple ITO/P3HT:PCBM/Al structure and its performance is compared with that of OPVC fabricated by incorporating an additional conducting layer of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) in between the active layer and ITO. An improvement of power conversion efficiency (PCE) has been observed from 2.716% to 2.733% due to the incorporation of PEDOT:PSS. The PCE has been further enhanced by replacing PEDOT:PSS with composites of carbon nanotubes (CNTs)/PEDOT:PSS and reduced graphene oxide (RGO)/PEDOT:PSS which have been prepared by simple solution method and the device parameters of all OPVCs are collated. A maximum PCE of 2.823% with corresponding short-circuit current density (Jsc) of 9.858 mA/cm2, open-circuit voltage (Voc) of 646.923 mV, and a fill factor (FF) of 44.263% has been achieved (at 25 °C) for the device with 5 wt% of CNTs in PEDOT:PSS. The performances of all fabricated OPVCs have been compared at different temperatures (25 °C, 30 °C, and 35 °C) and a declination in PCE is noted with increase in temperature. The stability of selected devices exposed to open atmosphere has been checked by measuring their parameters at different time intervals and it is observed that the degradation of materials reduces the performance of OPVCs. Under all different circumstances, OPVCs fabricated using the composites have been observed to perform better along with significant enhancement in PCE compared to OPVCs fabricated without using the composites.

Investigation of VTP:PC71BM organic composite as highly responsive organic photodetector

In this work, we report the use of vanadyl 3,10,17,24-tetra-tert-butyl-1,8,15,22-tetrakis(dimethylamino)-29H,31H-phthalocyanine (VTP) in the fabrication of organic photodetector that aimed to be more responsive in the lower region of visible light. The thin active layer of the photodetector has been developed from the vanadyl 3,10,17,24-tetra-tert-butyl-1,8,15,22-tetrakis(dimethylamino)-29H,31H-phthalocyanine (VTP) [6,6]:-phenyl C71 butyric acid methyl ester (PC71BM) blend solution. The combination of VTP and PC71BM has significantly enhanced the absorption of visible light especially below 650 nm for the ITO/PEDOT:PSS/VTP:PC71BM/Al photodetector. The detector showed good photocurrent-illumination linearity, fast response-recovery time and high consistency towards the rapid change of light intensities. It is found that the detector exhibits a good photoresponsivity of 2.30 × 10-1 A/W.

Alternative Thieno[3,2-b][1]benzothiophene Isoindigo Polymers for Solar Cell Applications.

This work reports the synthesis, characterization, photophysical, and photovoltaic properties of five new thieno[3,2-b][1]benzothiophene isoindigo (TBTI)-containing low bandgap donor-acceptor conjugated polymers with a series of comonomers and different side chains. When TBTI is combined with different electron-rich moieties, even small structural variations can have significant impact on thin film morphology of the polymer:phenyl C70 butyric acid methyl ester (PCBM) blends. More importantly, high-resolution electron energy loss spectroscopy is used to investigate the phase-separated bulk heterojunction domains, which can be accurately and precisely resolved, enabling an enhanced correlation between polymer chemical structure, photovoltaic device performance, and morphology.

Microwave exposure as a fast and cost-effective alternative of oxygen plasma treatment of indium-tin oxide electrode for application in organic solar cells

Pre-treatment methods are commonly employed to clean as well as to modify electrode surfaces. Many previous reports suggest that modifying the surface properties of indium tin oxide (ITO) by oxygen plasma treatment is a crucial step for the fabrication of high performance organic solar cells. In this work, we propose a fast and cost-effective microwave exposure step for the modification of the surface properties of ITO anode electrodes used in organic solar cells. It is demonstrated that a short microwave exposure improves the hydrophilicity and reduces the roughness of the ITO surface, as revealed by contact angle and atomic force microscopy (AFM) measurements, respectively, leading to a better quality of the PEDOT:PSS film coated on top of it. Similar results were obtained with the commonly used oxygen plasma treatment of ITO suggesting that microwave exposure is an effective process for modifying the surface properties of ITO with the benefits of low-cost, easy and fast processing. In addition, the influence of the microwave exposure of ITO anode electrode on the performance of an organic solar cell based on the poly(3-hexylthiophene):[6,6]-phenyl C70 butyric acid methyl ester (P3HT:PC70BM) blend is investigated. The 71% efficiency enhancement obtained in the microwave annealed-ITO based device as compared to the device with the as-received ITO was mainly attributed to the improvement in the short circuit current (Jsc) and decreased leakage current caused by the reduced series and the increased shunt resistances and also by the higher charge generation efficiency, and the reduced recombination losses.

High‐Performance Wide Bandgap Copolymers Using an EDOT Modified Benzodithiophene Donor Block with 10.11% Efficiency

AbstractNewly developed benzo[1,2‐b:4,5‐b′]dithiophene (BDT) block with 3,4‐ethylenedioxythiophene (EDOT) side chains is first employed to build efficient photovoltaic copolymers. The resulting copolymers, PBDTEDOT‐BT and PBDTEDOTFBT, have a large bandgap more than 1.80 eV, which is attributed to the increased steric hindrance between the BDT and EDOT skeletons. Both copolymers possess the satisfied absorptions, low‐lying highest occupied molecular orbital (HOMO) levels and high crystallinity. Using the fluorination strategy, PBDTEDOT‐FBT exhibits a wider and stronger absorption and a deeper HOMO level than those of PBDTEDOT‐BT. PBDTEDOT‐FBT:[6,6]‐Phenyl C71 butyric acid methyl ester (PC71BM) blend also shows the higher hole mobility and better surface morphology compared with the PBDTEDOTBT:PC71BM blend. Combination of above advantages, PBDTEDOT‐FBT devices exhibit much higher power conversion efficiency (PCE) of 10.11%, with an improved open circuit voltage (Voc) of 0.86 V, short circuit current densities (Jsc) of 16.01 mA cm−2, and fill factor (FF) of 72.6%. This work not only provides a newly efficient candidate of BDT donor block modified with EDOT conjugated side chains, but also achieves high‐performance large bandgap copolymers for polymer solar cells (PSCs) via the synergistic effect of fluorination and side chain engineering strategies.

Effect of optical intensity distribution on device performances of PTB7-Th:PC71BM-based organic photovoltaic cells

Abstract In order to realize high performance of organic photovoltaic cells (OPVs), it is indispensable to optimize device structures according to composing materials. In particular, the optical density distribution in stacked layers is one of important factors to enhance the optical absorption within the photoactive layer, resulting in the improved photoconversion efficiency. In this study, we optimized the film thickness of the photoactive layer as a fundamental way to control the optical density distribution. The influence of the photoactive layer thickness on photovoltaic performances of OPVs was first investigated using, poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b′]dithiophene-2,6diyl-alt-(4-(2-ethylhexyl)-3-uorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl)] and [6,6]-phenyl C 71 -butyric acid methyl ester blend films in normal and inverted OPV structures, respectively. The short circuit current density (J sc ) showed a peak at the thickness at around 100–120 nm and 80–100 nm in normal and inverted OPVs, respectively. In addition, J sc of inverted OPVs were higher than those of normal OPVs for all the thicknesses. The FF decreased continuously with increasing the thickness in both device structures. The fill factor of normal OPV decreased with increasing thickness more slowly than that of the inverted OPV at the thickness of over than 200 nm. Furthermore, we simulated the optical density distribution in the stacked layers using the algorithm utilized matrix formulas based on Abeles's formulas. The simulated optical intensity distribution as a function of the position and the wavelength is in a good agreement with the experimental spectra of external quantum efficiency. The result indicates a close correspondence between the optical density distribution and the photovoltaic performance. At the optimum photoactive layer thickness of 116 nm in the normal and 76 nm in the inverted OPVs, we obtained the highest PCEs of 9.25 and 10.4%, respectively.

Improved efficiency and stability in polymer solar cells using a Tetra-nuclear Zinc(II) complex interfacial layer

Abstract Tetra-nuclear Zinc(II) complex Zn 4 O(AID) 6 [AID = 7-azaindolate] is a wide band gap luminescent material that exhibits efficient emission matching the absorption spectra of organic donor materials such as polythiophene (P3HT). This work demonstrates polymer solar cells (PSC) based on P3HT:PCBM (phenyl-C 61 -butyric acid methyl ester) blend active layer with a Zn 4 O(AID) 6 cathode interfacial layer achieving a power conversion efficiency (PCE) significantly higher than that of the reference devices. The energy level and impedance spectroscopy analysis show that the Zn 4 O(AID) 6 cathode interfacial layer acts as an efficient exciton/hole blocking layer, and reduces charge recombination rate with more efficient electron extraction. The Zn 4 O(AID) 6 interfacial layer also helps achieve longer lifetime of PSC devices. The improved efficiency and stability combined with low cost and nontoxicity of Zn 4 O(AID) 6 make it a promising cathode interfacial material for high-performance and stable PSC devices.

Efficient and 1,8-diiodooctane-free ternary organic solar cells fabricated via nanoscale morphology tuning using small-molecule dye additive

The ternary strategy for incorporating multiple photon-sensitive components into a single junction has emerged as an effective method for optimizing the nanoscale morphology and improving the device performance of organic solar cells (OSCs). In this study, efficient and stable ternary OSCs were achieved by introducing the small-molecule dye (5E,5′E)-5,5′-(4′,4″-(1,2-diphenylethene-1,2-diyl)bis(biphenyl-4′,4-diyl))bis(methan-1-yl-1-ylidene)bis(3-ethyl-2-thioxothia zolidin-4-one) (BTPE-Rn) into poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-co-3-fluorothieno[3,4-b]thiophene-2-carboxylate] (PTB7-Th):[6,6]-phenyl C71 butyric acid methyl ester (PC71BM) blend films processed using a 1,8-diiodooctane (DIO)-free solvent. The incorporation of BTPE-Rn enhanced the short-circuit current density and fill factor of the ternary OSCs compared with those of binary OSCs. An investigation of the optical, electronic, and morphological properties of the ternary blends indicated that the third component of BTPE-Rn not only promoted the photon utilization of blends through the energy-transfer process but also improved the electron mobility of the blends owing to the fullerene-rich nanophase optimization. More importantly, this ternary strategy of utilizing a small-molecule dye to replace the photounstable DIO additive enhanced the operational stability of the OSCs.

Toward Long-Term Stable and Efficient Large-Area Organic Solar Cells.

Here, we report that long-term stable and efficient organic solar cells (OSCs) can be obtained through the following strategies: i) combination of rapid-drying blade-coating deposition with an appropriate thermal annealing treatment to obtain an optimized morphology of the active layer; ii) insertion of interfacial layers to optimize the interfacial properties. The resulting devices based on poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b']dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-2-carboxylate-2,6-diyl)] (PBDTTT-EFT):[6,6]-phenyl C71 butyric acid methyl ester (PC71 BM) blend as the active layer exhibits a power conversion efficiency (PCE) up to 9.57 %, which represents the highest efficiency ever reported for blade-coated OSCs. Importantly, the conventional structure devices based on poly(3-hexylthiophene) (P3HT):phenyl-C61 -butyric acid methyl ester (PCBM) blend can retain approximately 65 % of their initial PCE for almost 2 years under operating conditions, which is the best result ever reported for long-term stable OSCs under operational conditions. More encouragingly, long-term stable large-area OSCs (active area=216 cm2 ) based on P3HT:PCBM blend are also demonstrated. Our findings represent an important step toward the development of large-area OSCs with high performance and long-term stability.

Large branched alkylthienyl bridged naphtho[1,2-c:5,6-c′]bis[1,2,5]thiadiazole-containing low bandgap copolymers: Synthesis and photovoltaic application

ABSTRACTTwo donor-acceptor (D-A) type low bandgap (LBG) alternating conjugated copolymers containing larger conjugation planarity and stronger electro-withdrawing ability naphtho[1,2-c:5,6-c′]bis[1,2,5]thiadiazole (NT) unit, namely, poly[4,8-bis(5-(n-octylthio)thien-2-yl)-benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl-alt-4,9-bis(4-(2-decyltetradecyl)thien-2-yl)naphtho- [1,2-c:5,6-c′]bis[1,2,5]thiadiazole-5,5′-diyl] (PBDT-TS-DTNT-DT) and poly[4,8-bis(triiso-propylsilylethynyl)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl-alt-4,9-bis(4-(2-decyltetradecyl)-thien-2-yl)naphtho[1,2-c:5,6-c′]bis[1,2,5]thiadiazole-5,5′-diyl] (PBDT-TIPS-DTNT-DT), were prepared by the palladium-catalyzed Stille polycondensation and characterized by gel permeation chromatography (GPC), UV-Vis absorption, thermal gravimetric analysis (TGA), cyclic voltammetry (CV) etc. PBDT-TS-DTNT-DT and PBDT-TIPS-DTNT-DT show the broader absorption and deeper highest occupied molecular orbital (HOMO) energy level approximately −5.45 and −5.62 eV, respectively. Bulk-heterojuction solar cells based on the resulted polymers and [6,6] phenyl-C61 butyric acid methyl ester (PC61BM) blends, with the device configuration of ITO/PFN/polymer:PC61BM/MoO3/Ag were prepared and investigated. The results showed the power conversion efficiency (PCE) of 2.67% for PBDT-TS-DTNT-DT/PC61BM (w:w, 1:2) and 0.64% for PBDT-TIPS-DTNT-DT/PC61BM (w:w, 1:1), with relatively high open-circuit voltage (VOC) of 0.86 and 1.05 V, small short-circuit current (JSC) of 5.41 and 0.97 mA cm−2 and moderate fill factor (FF) of 57.8% and 62.4%, under an AM1.5 simulator (100 mWcm−2), respectively.

Photodegradation of Metal Oxide Interlayers in Polymer Solar Cells

The effect of 1 sun illumination for 24 h on encapsulated inverted organic photovoltaic devices is studied through a series of electrical and optical characterizations for donor/acceptor polymer solar cells based on poly(dithienogermole‐alt‐thienopyrrolodione)/[6,6]‐phenyl C71 butyric acid methyl ester blends. Power conversion efficiency is significantly reduced after light exposure due to a 45% drop in the device fill factor and a 40% drop in both the open circuit voltage and short circuit current. The decrease in open circuit voltage is attributed to a reduction in the built‐in field in the device due to photodegradation of the ZnO interlayer. The reduction in fill factor and short circuit current is shown to be due to the formation of an extraction barrier for hole collection as a result of photodegradation of the MoOx interlayer. Using a 400 nm long pass filter to block the UV light, device stability is significantly enhanced, resulting in a decrease in power conversion efficiency of less than 5% under the same operation conditions.

Luminescent cathode buffer layer for enhanced power conversion efficiency and stability of bulk-heterojunction solar cells

We report high photovoltaic efficiency of over 9% in solution-processed, small-molecule (SPSM) 7,7′-(4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b′]dithiophene-2,6-diyl)bis(6-fluoro-4(5′-hexyl-[2,2′-bithiophen]-5-yl)benzo[c]1,2,5]thiadiazole) p-DTS(FBTTh2)2:[6-6]-phenyl C70 butyric acid methyl ester (PC70BM) blend based inverted BHJ solar cell by incorporating luminescent zinc oxide doped with sodium (ZnO:Na) quantum dots (QD) (l-ZnO) as a cathode buffer layer (CBL) in inverted bulk-heterojunction (BHJ) solar cells for the first time. The l-ZnO absorbs ultraviolet (UV) light and down-converts it to visible light. The l-ZnO layer's emission overlaps significantly with the absorption of p-DTS(FBTTh2)2, leading to an enhanced absorption by p-DTS(FBTTh2)2. This resulted in a significant enhancement of photo-current from 15.4 to 17.27 mA/cm2 and efficiency from 8% to 9.2% for ZnO and l-ZnO based devices, respectively. This is among one of the highest efficiency values reported so far in the case of SPSM based single junction BHJ solar cells. The luminescent ZnO layer also protects the active layer from UV-induced degradation as solar cells show high stability under constant solar light illumination retaining more than 90% (∼28 h) of its initial efficiency, whereas BHJ solar cells without the luminescent ZnO layer degraded to ∼50% of its initial value under same conditions. Since ZnO is an essential part of inverted organic solar cells, the luminescent l-ZnO CBL has great potential in inverted organic solar cells.

Systematic optimization of low bandgap polymer/[6,6]-phenyl C70 butyric acid methyl ester blend photodiode via structural engineering

Synthetic approaches for optimizing polymer-based organic photodiodes (OPDs) by systematically analyzing the effects of the hole-blocking layer, the electron-blocking layer, and the thickness and morphology of the active layer with respect to the dark current and detectivity have been reported. PBDTT-DPP with a repeating alkylthienylbenzodithiophene (BDTT) and diketopyrrolopyrrole (DPP) units is used as a p-type polymer for achieving both broadband absorption and a high absorption coefficient in conjunction with n-type [6,6]-phenyl C70 butyric acid methyl ester (PC70BM) for constructing photoactive layers. Through systematic investigations of various interfacial layers, we found that the thickness of the active layer and the energy level of the hole/electron blocking layer were critical for minimizing the dark current of OPDs. By changing the deposition method of the PBDTT-DPP/PC70BM blend and using post treatment, we discovered that the morphology of the active layer was directly related to the photocurrent of OPDs. Furthermore, we conducted a comparative study between a bulk heterojunction and a planar heterojunction (PHJ) to demonstrate the effectiveness of the PHJ for suppressing the dark current. Consequently, we realized a high detectivity of 5.3 × 1012 Jones with an optimized device architecture and morphology. This work shows the importance of a synthetic approach for optimizing OPDs that requires both a high photocurrent and a low dark current in the reverse saturation regime.

An insight on oxide interlayer in organic solar cells: From light absorption and charge collection perspectives

A comprehensive study of the effect of oxide interlayer on the performance of bulk-heterojunction organic solar cells (OSCs), based on poly[[4,8-bis[(2-ethylhexyl)oxy] benzo [1,2-b:4,5-b'] dithiophene-2,6- diyl] [3-fluoro-2-[(2-ethylhexyl)carbonyl] thieno [3,4-b] thiophenediyl]] (PTB7): [6,6]-phenyl C71 butyric acid methyl ester (PC70BM) blend system, is carried out by optical simulation, interfacial exciton dissociation and charge collection analyses. It is found that a PTB7:PC70BM blend layer thickness optimized for maximum light absorption in OSCs does not generally give rise to the highest power conversion efficiency (PCE). OSCs, e.g., based on PTB7:PC70BM blend system, can benefit from the oxide interlayer in two ways, (1) to enhance the built-in potential for reducing recombination loss of the photo-generated charges, and (2) to improve charge collection by removal of unfavorable interfacial exciton dissociation. The combined effects result in ∼20% improvement in PCE over an optimized control cell, having an identical layer configuration without an oxide interlayer.