PCBM Blend Research Articles

Effects of 1,8-diiodooctane on ultrafast charge carrier dynamics and photovoltaic performance in organic solar cells: A comparison of PC71BM and nonfullerene acceptor IT-M

Abstract Nonfullerene acceptors are currently dominating the research and development of organic photovoltaics (OPVs). Exploring the charge separation mechanism is helpful to understand the photovoltaic process in efficient nonfullerene-based OPVs. Herein, we have selected two typical acceptors: PC71BM and nonfullerene acceptor IT-M, and have studied the device function and the ultrafast charge carrier dynamics in the PBDB-TF:IT-M and PBDB-TF:PC71BM blends to investigate how they are affected by different blend morphologies induced by using a popular solvent additive 1,8-diiodooctane (DIO). It is found that ultrafast charge generation occurs in both of the two blend systems. For the IT-M blend film, the DIO additive strongly affects the ultrafast photophysical process. Efficient hole transfer is observed for the IT-M blend processed with DIO compared to the pristine IT-M blend. Moreover, the charge density is significantly increased in the DIO-processed IT-M blend film. In contrast to the IT-M blend, the DIO does not strongly affect the ultrafast charge carrier dynamics in PC71BM blend possibly due to its slight effect on the blend morphology. The reionization of spin-triplet charge transfer states can occur faster than relaxation to triplet in both of the well-ordered blend film processed with DIO resulting in an enhanced current density and fill factor.

Design of novel thiazolothiazole-containing conjugated polymers for organic solar cells and modules

One of the major challenges in the field of organic photovoltaics is associated with high-throughput manufacturing of efficient and stable organic solar cells. Practical realization of technologies for production of large-area organic solar cells requires the development of novel materials with a defined combination of properties ensuring sufficient reliability and scalability of the process in addition to good efficiency and operation stability of the devices. In this work, we designed two novel polymers comprising thiazolothiazole units and investigated their performance as absorber materials for organic solar cells and modules. Optimized small-area solar cells based on P1/[70]PCBM ([6,6]-phenyl-C71-butyric acid methyl ester) blends exhibited promising power conversion efficiency (PCE) of 7.5%, while larger area modules fabricated using slot die coating showed encouraging PCE of 4.2%. Additionally, the fabricated devices showed promising outdoor stability maintaining 60–70% of the initial efficiency after 20 sun days being exposed to natural sunlight at the Negev desert. The obtained results feature the designed polymer P1 as a promising absorber material for a large-scale production of organic solar cells under ambient conditions.

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.

Phase diagram of P3HT:PC70BM thin films based on variable-temperature spectroscopic ellipsometry

In this article, we present the research on the influence of the composition of thin films of a blend of poly (3-hexylthiophene −2,5-diyl) - P3HT with fullerene derivatives [6,6]-phenyl-C71-butyric acid methyl ester – PC70BM and [6,6]-phenyl-C61-butyric acid methyl ester – PC60BM on their thermal transitions. The influence of molar mass (Mw) of P3HT (Mw = 65.2; 54.2 and 34.1 kDa) and PCBM (PC60BM – Mw = 911 g/mol and PC70BM – Mw = 1031 g/mol) is examined in details. The article presents significantly expanded research compared to our previous work on thermal transitions in thin films of blend P3HT (Mw = 65.2 kDa) with PC60BM. For this reason, we also compare current results with previous ones. Here, we present for the first time a phase diagram of thin films of the P3HT(Mw = 65.2 kDa):PC70BM blend using variable-temperature ellipsometry. Our research reveals the presence of characteristic temperatures of pure phases in thin films of P3HT: PCBM blends. It turns out that the cold crystallization temperature of the P3HT phase in P3HT(Mw = 65.2 kDa):PC70BM blend films is lower than corresponding temperature in P3HT(Mw = 65.2 kDa):PC60BM blend films. At the same time, the cold crystallization temperature of the PC70BM phase behaves inversely. We demonstrate also that variable-temperature spectroscopic ellipsometry is a very sensitive technique for studying thermal transitions in these thin films. In addition, we show that the entire phase diagram can be determined based on the raw ellipsometric data analysis, e.g. using a delta angle at wavelength λ = 280 nm.

Enhancing P3HT/PCBM blend stability by thermal crosslinking using poly(3-hexylthiophene)-S,S-dioxide

A statistical copolymer containing thiophene and thiophene-S,S-dioxide rings was utilized as a thermal crosslinker in a blend of P3HT and PCBM, demonstrating an effective strategy for preventing agglomeration of PCBM and enhancing blend stability.

The impact of thermal treatment on the performance of benzo[1,2-b:4,5-b']difuran-based organic solar cells.

The new low bandgap benzo[1,2-b:4,5-b′]difuran (BDF)-based organic small molecule, namely B1, was synthesized by Stille coupling polymerization reactions. B1 was found to be soluble in common organic solvents such as chloroform, toluene and chlorobenzene with excellent film forming properties. The structure of B1 was verified by 1H NMR, GC-MS and elemental analysis. The B1 films exhibit broad absorption bands from 300 to 750 nm. The hole mobility of B1 : PC61BM (1 : 1, w/w) blend film reached up to 7.7 × 10−2 cm V−1 s−1 after thermal annealing by the space-charge-limited current method. BHJ organic solar cells (OSCs) were fabricated with a device structure of ITO/PEDOT : PSS/B1 : C61BM/LiF/Al. When the active layer was thermally annealed at 120 °C, B1 showed the best photovoltaic performance, with a PCE up to 5.0%. We also studied the connection between the morphologies of the active layers and the photovoltaic performance by AFM, PL, etc. Our observation will guide future design for even better small molecules for highly efficient OSCs.

Cd doped Ba (NO3)2 nanoparticle as broadband solar absorber in thin film organic solar cell

AbstractEnhanced photocurrent was observed by embedding Cd doped Ba (NO3)2 nanoparticle composite in the photoactive layer of bulk heterojunction organic solar cell. The research was conducted based on P3HT: PCBM blend active layer containing Cd doped Ba (NO3)2 at various concentrations. The best performance of the fabricated devices was found to be dependent on the concentration of the composite nanoparticle. A substantial improvement in PCE of 5.01% compared to 3.25% of the pristine device was obtained. The optical and electrical properties of the fabricated devices were carried out. Also, the structural properties of the nanoparticle composite were established.

Influence of blend composition and annealing temperature on optical properties of organic photovoltaic cell based on P3HT:PCBM interpenetrating blend

ABSTRACTIn this paper, the influence of blend composition and annealing temperature on optical properties of organic photovoltaic (OPV) cells based on P3HT:PCBM interpenetrating blend is presented. Optical optimization of the OPV cell is first performed to determine the optimal geometry of the stack. The studied device structure is: glass/ITO/PEDOT:PSS/P3HT:PCBM/Ca/Al. Simulation results give as optimized thicknesses: dPEDOT:PSS = 27 nm and dActive layer = 91 nm. The optimized OVP cell gives a short-circuit current JSC = 12.48 mA/cm2. The influence of technological parameters on the performance of the optimized P3HT:PCBM blend OPV cell is then clearly defined. Simulation results show that among the mass ratio of P3HT:PCBM blend active layers studied (1:1, 1:2, 2:1, 2:3 and 3:2), the active layer with the higher blend mass ratio (2:1) gives the best optical properties. Also, increasing the annealing temperature of the active layer leads to increase absorption. The blend active layer annealed at 140°C presents the best optical properties of the OPV cell.

A systematic evaluation of triisopropylsilylethynyl-substituted thienyl side chain effects on series of benzo[1,2-b:4,5-b′]dithiophene based polymer donors and their photovoltaic performances

In this report three new donor copolymers based on alternate octyl 3-fluorothieno[3,4-b]thiophene-2-carboxylate as acceptor and benzo[1,2-b:4,5-b′]dithiophene (BDT) derivatives having triisopropylethynylsilane (TIPS), triisopropyl((thiophen-2-yl)ethynyl)silane (TIPS-Th) and triisopropyl((3-octylthiophen-2-yl)ethynyl)silane (TIPS-ThC8) side chains as donors, (respectively named as P1, P2 and P3) are synthesized to assess whether insertion of thiophene or alkyl thiophene units between TIPS side chains and BDT backbones can improve their properties and photovoltaic performance. Indeed, the modification of TIPS side chains on BDT backbone found to distinctly affect their opto-electrochemical properties, molecular orientations and nanoscale morphologies in resultant polymers. Among the polymers, optimized organic solar cells (OSCs) of P1:PC71BM exhibited best power conversion efficiency (PCE) of 6.55% with a very high VOC of 1.02 V, thereby outperforming P2 and P3 (PCE of 4.72% and 5.47%, respectively). The detailed characterization of optimized blends revealed that this superior device performance of P1:PC71BM blend films attributed to their compact and “face-on” molecular orientation, high hole mobility and superior nanoscale morphology, which minimized voltage loss and leading to an efficient charge transfer with low recombination losses in OCSs. In contrast, lower performances of P2 and P3 were mainly originating from their decreased solubilities caused by the insertion of TIPS-Th or TIPS-ThC8, thereby negatively affecting their molecular weights, morphology and charge carrier mobilities. Thus, these results provide a valuable guideline for designing polymers based on 2-TIPSTh substituted BDT units.

Roll-to-roll micro-gravure printed P3HT:PCBM organic solar cells

Roll-to-roll (R2R) micro-gravure printing is an attractive technology for fabricating organic solar cells (OSCs) at low cost with high throughput. The nanoscale morphology and phase separation of R2R micro-gravure printed active layers have a large influence on the photovoltaic performance of OSCs. Herein, we demonstrate that the photovoltaic performance of R2R micro-gravure printed P3HT:PCBM OSCs can be enhanced by optimizing phase separation using solvent engineering. R2R micro-gravure printed P3HT:PCBM blend film with chlorobenzene solvent enabled optimized phase separation and formation of a fine-tuned interpenetrating network in a bulk heterojunction (BHJ) layer compared with a film with 1,2-dicholorobenzene solvent. This creates an optimal transport pathway and therefore effectively enhances charge transport in the BHJ blend film and boosts device performance. This research shows that high-performance OSCs could be fabricated by large-scale, R2R micro-gravure printing with solvent engineering, which would accelerate the development of fully R2R micro-gravure printed flexible OSCs.

Rational Design of 2D p–π Conjugated Polysquaraines for Both Fullerene and Nonfullerene Polymer Solar Cells

AbstractSo far, squaraine‐based polymer donors have been less explored for the bulk heterojunction (BHJ) polymer solar cells. In this work, two new p–π conjugated polysquaraines (PASQ‐BDT1 and PASQ‐BDT2) with different electron‐rich subunits on the squaraine skeleton are rationally developed as new polymer donors based on the 2D structure design concept. PASQ‐BDT2 with N,N‐diisobutylaniline subunits shows superior device performances in both fullerene and nonfullerene PSCs compared to PASQ‐BDT1 containing triphenylamine subunits, with power conversion efficiencies (PCEs) of 4.34% and 3.72%, respectively, owing to increased light‐harvesting ability and more favorable nanoscale morphology in the BHJ films. Moreover, its demonstrated that solvent effects can play an effective role in elevating the device performance. For the PASQ‐BDT2/PC71BM blend, the PCE is improved from 3.19% to 4.34% after solvent vapor annealing treatment, mainly attributed to the optimized film morphology and increased hole mobility. More interestingly, when the processing solvent for nonfullerene devices is changed from chlorobenzene to chloroform, a significant enhancement on PCE from 1.96% to 3.72% is yielded for the PASQ‐BDT2/ITIC blend, due to suppressed charge recombination and enhanced crystallinity in the chloroform‐processed BHJ films.

Metal nano-composite assisted photons harvesting in thin film organic photovoltaic

Nickel oxide (NiO) nano-particles assisted photons harvesting is studied using P3HT:PCBM blend based bulk heterojunction thin film organic solar cell (TFOSC). A comparison between devices that were fabricated at different concentration of NiO and that of the pristine P3HT:PCBM active layer were drawn up. The experimental results suggest that the incorporation of NiO in the solar absorber medium was found to be favourable for solar energy harvesting. At optimum concentration of NiO, in P3HT:PCBM blend active layer, the power conversion efficiency has grown by over 140% compared to the pristine type of devices. Moreover, significant improvement were also recorded on the solar cell fill factor (FF) and short circuit current density (JSC), respectively. The newly fabricated solar cells are discussed in terms of the optical and electrical properties of the solar absorber film.

Functionalized and reduced graphene oxide as hole transport layer and for use in ternary organic solar cell

Here is reported the performance of organic solar cells (OSCs) by using a new graphene oxide derivative as hole transport layer (HTL). OSCs are based on the PTB7:PC71BM blend as active layer and the alternative top electrode Field's metal (Bi/In/Sn: 32.5%, 51%, 16.5%), which can be easily deposited through a vacuum-free process at regular atmosphere and low temperature (90 °C). Graphene oxide (GO) was chemically functionalized and reduced with pentafluorophenylhydrazine, this fluorinated reduced graphene oxide (F5-rGO) was suspended in dimethylformamide for easy deposit by wet techniques such as spin-cast. F5-rGO has a work-function of 5.1 eV due to the high electronegativity of fluorine atoms incorporated into the GO sheets. The best achieved PCE of the OSCs fabricated for a single layer of F5-rGO was 5.82%. An enhanced PCE of 7.67% when F5-GO was used as interlayer between ITO and PEDOT:PSS was reached (PCE of PEDOT:PSS-based was 7.29%). Additionally, functionalized and reduced (chemically) graphene oxide (H5-rGO) was also obtained from GO treated with phenylhydrazine, and ternary OSCs were also prepared by adding H5-rGO to the PTB7:PC71BM blend at different weight ratios: 0, 3, and 6%. The best results were achieved with 3% of H5-rGO: OSCs presented a PCE of 7.56%.

Quaternary Solar Cells with 12.5% Efficiency Enabled with Non-Fullerene and Fullerene Acceptor Guests to Improve Open Circuit Voltage and Film Morphology.

Designing the bulk-heterojunction structure (binary, ternary and quaternary) is of great fundamental interest for relaxing the trade-off between open circuit voltage (Voc ) and short circuit current density ( Jsc ). Herein, a new quaternary blended material system is reported with a nonfullerene and PC71 BM as the third and fourth component of PBDB-T:ITCT, leading to simultaneously increased Voc and Jsc and maintained fill factor (FF). The guest IT-T-IC has upshifted LUMO energy level helping to obtain a higher Voc . The further addition of 0.2 PC71 BM as the fourth component yields an even higher Voc because the LUMO of PC71 BM is higher than that of ITCT. Interestingly, the blend of PC71 BM leads to the formation of an unprecedented neuron-like morphology, which acts as new centers not only performing light absorption and charge separation but also charge transport through their surrounding donor and acceptor fibers. The increased hole and electron mobilities and the reduced bimolecular loss results in an even larger Jsc and FF. These results indicate that a combination using a structurally similar higher-LUMO-level non-fullerene acceptor and PCBM is a simple yet effective quaternary material approach to simultaneously increase Voc and Jsc while maintaining FF, improving final device performance.

Investigation the effect of post deposition thermal treatment on properties P3HT and P3HT:PCBM blend.

This work reports the study of heat treatment effect on the structural, morphological, optical and electrical properties of poly [3-hexylthiophene] and its blend with [6,6]-phenyl C61 butyric acid methyl ester ( P3HT:PC61BM). X-ray diffraction (XRD) measurements show that the crystallinity of the films increased with annealing. The evaluation of surface roughness and morphology was investigated using atomic force microscope (AFM), and field emission scanning microscope(FESEM). The optical properties were emphasized a strong optical absorption of P3HT compared with the blend. Hall effect measurement was used to study the electrical properties which revealed there is an increase in the electrical conductivity and Hall mobility of the p-type P3HT and its blend with heat treatment.

Double-sided asymmetric surface modification of ZnO interfacial layer to enhance performance in organic solar cells

Surface modification of the widely used ZnO interfacial layer is a crucial issue for the development of photoelectric devices toward high efficiency and long-term stability. Most conventional surface modifications of ZnO interfacial layers involve only a one-sided modification (e.g., a ZnO/active layer interface), which limits the electrical and electronic performance of the resulting interfacial layer. Herein, we report a double-sided surface modification strategy in which both sides of the ZnO interfacial layer are modified. The resulting double-sided modified ZnO layers are used to enhance the photovoltaic performance of inverted organic solar cells as electron-transporting layers (ETLs). Compared with devices based on unmodified ZnO interfacial layers, the power conversion efficiencies of devices using the modified ZnO interfacial layer are markedly enhanced, from 3.42% to 4.23% for the P3HT:PC61BM active layer, and from 7.57% to 8.61% for the PTB7:PC71BM blend system. The enhancements in photovoltaic performance result mainly from the modified energy level alignment and improved interface contact quality between the ETL and active layer, which help to reduce the interfacial energy barrier between the active layer and indium tin oxide electrode, thereby enhancing the electron collection and transport efficiency. More importantly, this double-sided surface modification strategy could be easily extended to modify the interfacial layers of other photoelectric devices, such as perovskite solar cells, quantum dot solar cells and organic light-emitting diodes.

16.67% Rigid and 14.06% Flexible Organic Solar Cells Enabled by Ternary Heterojunction Strategy.

Ternary heterojunction strategies appear to be an efficient approach to improve the efficiency of organic solar cells (OSCs) through harvesting more sunlight. Ternary OSCs are fabricated by employing wide bandgap polymer donor (PM6), narrow bandgap nonfullerene acceptor (Y6), and PC71 BM as the third component to tune the light absorption and morphologies of the blend films. A record power conversion efficiency (PCE) of 16.67% (certified as 16.0%) on rigid substrate is achieved in an optimized PM6:Y6:PC71 BM blend ratio of 1:1:0.2. The introduction of PC71 BM endows the blend with enhanced absorption in the range of 300-500 nm and optimises interpenetrating morphologies to promote photogenerated charge dissociation and extraction. More importantly, a PCE of 14.06% for flexible ITO-free ternary OSCs is obtained based on this ternary heterojunction system, which is the highest PCE reported for flexible state-of-the-art OSCs. A very promising ternary heterojunction strategy to develop highly efficient rigid and flexible OSCs is presented.

Bulk heterojunction polymer solar cell, using ZnO nanorods with various mass ratios of P3HT:PCBM blend as the active layer

The present study investigated the influence of employing various mass ratios of the P3HT:PCBM blend as an active layer using the doctor blade technique with a speed of 40 mm/s. ZnO nanostructure and ZnO nanorods (NRs) were utilized in an inverted bulk heterojunction organic solar cell as an electron transport layer. The temperature in annealing was 140 °C. The active layer played a significant role in increment hole mobility and balanced charge transport. The samples were examined by the X-ray diffraction, scanning electron microscopy, UV–visible transmission spectra. The use of P3HT:PCBM with a ratio of 1:0.9 on the top of the ZnO nanoparticles gave Jsc of 9.46 mm/s, Voc of 0.550 V, and a fill factor of 64.09% and resulted in a power conversion efficiency of 3.33%.

Organic Solar Cells Based on the Aggregate of Synthetic Chlorophyll Derivative with over 5% Efficiency

The power conversion efficiency (PCE) of chlorophyll (Chl)‐based organic solar cells (OSCs) is generally about 2%. Herein, a Chl‐a derivative (CHL) and [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC71BM) are successfully used to fabricate Chl‐based OSCs with PCE over 5%. Two different preparation methods are used to prepare the active layer: 1) two‐step spin‐coating the self‐aggregated CHL and PC71BM solutions sequentially and 2) one‐step spin‐coating the solution of CHL:PC71BM blends, forming the “bilayer” (BL) and traditional bulk heterojunction (BHJ) configurations, respectively. Based on the aforementioned two kinds of active‐layer preparation methods, both inverted and regular types of OSCs are successfully investigated. All four types of devices work normally, which is likely due to the ambipolar characteristics of the CHL aggregate. Unexpectedly, the BL‐based devices yield PCEs of 5.17% for the regular type and 5.19% for the inverted type, which are higher than those of the BHJ‐based devices (3.96% for the regular type and 3.50% for the inverted type). The main improvement in PCEs of BL‐based devices comes from the enhanced short‐circuit currents, which is due to the decreased charge transfer resistance and enlarged photocurrent contribution of PC71BM as well as slightly enhanced electron and hole mobilities.

Simple Approach to Overcome Thickness Tolerance of Interlayer without Sacrificing the Performances of Polymer Solar Cells

AbstractSmall‐molecule electrolyte (C6‐E‐OTs) hybridized ZnO layer is provided as the electron transporting layer. The device based on the blend of PTB7 and PC71BM as the active layer shows an enhanced power conversion efficiency (PCE) from 7.6% based on ZnO to 8.8% using the C6‐E‐OTs hybridized ZnO layer. The device can be further improved by simultaneously using a C6‐E‐OTs hybridized ZnO layer and a 5 nm thick C6‐E‐OTs as the interlayer. The synergy effect of hybridization and interlayer enhanced the PCE of the device to 8.9%, which is a 17.1% increase in comparison with the device based on ZnO. The presence of C6‐E‐OTs hybridized ZnO and a 5 nm of C6‐E‐OTs as the interlayer in the device with PTB7‐Th as the donor significantly improves the PCE from 8.0% based on ZnO to 9.4%, resulting in a 17.5% enhancement. Main contribution for enhancing the PCE of the device is the improved Jsc, which results from the reduction of energy offset at the cathode interface. Thus, hybridized ZnO layer process can overcome the limitation faced by the thickness tolerance of interlayer.