Optimal Structure for High‐Performance and Low‐Contact‐Resistance Organic Field‐Effect Transistors Using Contact‐Doped Coplanar and Pseudo‐Staggered Device Architectures

A low contact resistance achieved on top‐gated organic field‐effect transistors by using coplanar and pseudo‐staggered device architectures, as well as the introduction of a dopant layer, is reported. The top‐gated structure effectively minimizes the access resistance from the contact to the channel region and the charge‐injection barrier is suppressed by doping of iron(III)trichloride at the metal/organic semiconductor interface. Compared with conventional bottom‐gated staggered devices, a remarkably low contact resistance of 0.1–0.2 kΩ cm is extracted from the top‐gated devices by the modified transfer line method. The top‐gated devices using thienoacene compound as a semiconductor exhibit a high average field‐effect mobility of 5.5–5.7 cm² V^?1 s^?1 and an acceptable subthreshold swing of 0.23–0.24 V dec^?1 without degradation in the on/off ratio of ≈10⁹. Based on these experimental achievements, an optimal device structure for a high‐performance organic transistor is proposed.     

High‐Speed Organic Single‐Crystal Transistor Responding to Very High Frequency Band

Although high carrier mobility organic field‐effect transistors (OFETs) are required for high‐speed device applications, improving the carrier mobility alone does not lead to high‐speed operation. Because the cut‐off frequency is determined predominantly by the total resistance and parasitic capacitance of a transistor, it is necessary to miniaturize OFETs while reducing these factors. Depositing a dopant layer only at the metal/semiconductor interface is an effective technique to reduce the contact resistance. However, fine‐patterning techniques for a dopant layer are still challenging especially for a top‐contact solution‐processed OFET geometry because organic semiconductors are vulnerable to chemical damage by solvents. In this work, high‐resolution, damage‐free patterning of a dopant layer is developed to fabricate short‐channel OFETs with a dopant interlayer inserted at the contacts. The fabricated OFETs exhibit high mobility exceeding 10 cm² V^?1 s^?1 together with a reasonably low contact resistance, allowing for high frequency operation at 38 MHz. In addition, a diode‐connected OFET shows a rectifying capability of up to 78 MHz at an applied voltage of 5 V. This shows that an OFET can respond to the very high frequency band, which is beneficial for long‐distance wireless communication.     

A Noble Metal Dichalcogenide for High‐Performance Field‐Effect Transistors and Broadband Photodetectors

2D layered materials are an emerging class of low‐dimensional materials with unique physical and structural properties and extensive applications from novel nanoelectronics to multifunctional optoelectronics. However, the widely investigated 2D materials are strongly limited in high‐performance electronics and ultrabroadband photodetectors by their intrinsic weaknesses. Exploring the new and narrow bandgap 2D materials is very imminent and fundamental. A narrow‐bandgap noble metal dichalcogenide (PtS₂) is demonstrated in this study. The few‐layer PtS₂ field‐effect transistor exhibits excellent electronic mobility exceeding 62.5 cm² V^?1 s^?1 and ultrahigh on/off ratio over 10⁶ at room temperature. The temperature‐dependent conductance and mobility of few‐layer PtS₂ transistors show a direct metal‐to‐insulator transition and carrier scattering mechanisms, respectively. Remarkably, 2D PtS₂ photodetectors with broadband photodetection from visible to mid‐infrared and a fast photoresponse time of 175 µs at 830 nm illumination for the first time are obtained at room temperature. Our work opens an avenue for 2D noble‐metal dichalcogenides to be applied in high‐performance electronic and mid‐infrared optoelectronic devices.     

Phthalocyanine‐Based 2D Conjugated Metal‐Organic Framework Nanosheets for High‐Performance Micro‐Supercapacitors

2D conjugated metal‐organic frameworks (2D c‐MOFs) are emerging as a novel class of conductive redox‐active materials for electrochemical energy storage. However, developing 2D c‐MOFs as flexible thin‐film electrodes have been largely limited, due to the lack of capability of solution‐processing and integration into nanodevices arising from the rigid powder samples by solvothermal synthesis. Here, the synthesis of phthalocyanine‐based 2D c‐MOF (Ni₂[CuPc(NH)₈]) nanosheets through ball milling mechanical exfoliation method are reported. The nanosheets feature with average lateral size of ≈160 nm and mean thickness of ≈7 nm (≈10 layers), and exhibit high crystallinity and chemical stability as well as a p‐type semiconducting behavior with mobility of ≈1.5 cm² V^?1 s^?1 at room temperature. Benefiting from the ultrathin feature, the nanosheets allow high utilization of active sites and facile solution‐processability. Thus, micro‐supercapacitor (MSC) devices are fabricated mixing Ni₂[CuPc(NH)₈] nanosheets with exfoliated graphene, which display outstanding cycling stability and a high areal capacitance up to 18.9 mF cm^?2; the performance surpasses most of the reported conducting polymers‐based and 2D materials‐based MSCs.     

Relaxing the Conductivity/Transparency Trade‐Off in MOCVD ZnO Thin Films by Hydrogen Plasma

Increasing the conductivity of polycrystalline zinc oxide films without impacting the transparency is a key aspect in the race to find affordable and high quality material as replacement of indium‐containing oxides. Usually, ZnO film conductivity is provided by a high doping and electron concentration, detrimental to transparency, because of free carrier absorption. Here we show that hydrogen post‐deposition plasma treatment applied to ZnO films prepared by metalorganic low‐pressure chemical vapor deposition allows a relaxation of the constraints of the conductivity/transparency trade‐off. Upon treatment, an increase in electron concentration and Hall mobility is observed. The mobility reaches high values of 58 and 46 cm²V^?1s^?1 for 2‐μm‐ and 350‐nm‐thick films, respectively, without altering the visible range transparency. From a combination of opto‐electronic measurements, hydrogen is found, in particular, to reduce electron trap density at grain boundaries. After treatment, the values for intragrain or optical mobility are found similar to Hall mobility, and therefore, electron conduction is found to be no longer limited by the phenomenon of grain boundary scattering. This allows to achieve mobilities close to 60 cm²V^?1s^?1, even in ultra‐transparent films with carrier concentration as low as 10¹⁹ cm^?3.     

High‐Speed,Low‐Voltage,and Environmentally Stable Operation of Electrochemically Gated Zinc Oxide Nanowire Field‐Effect Transistors

Single‐crystal, 1D nanostructures are well known for their high mobility electronic transport properties. Oxide‐nanowire field‐effect transistors (FETs) offer both high optical transparency and large mechanical conformability which are essential for flexible and transparent display applications. Whereas the “on‐currents” achieved with nanowire channel transistors are already sufficient to drive active matrix organic light emitting diode (AMOLED) displays; it is shown here that incorporation of electrochemical‐gating (EG) to nanowire electronics reduces the operation voltage to ≤2 V. This opens up new possibilities of realizing flexible, portable, transparent displays that are powered by thin film batteries. A composite solid polymer electrolyte (CSPE) is used to obtain all‐solid‐state FETs with outstanding performance; the field‐effect mobility, on/off current ratio, transconductance, and subthreshold slope of a typical ZnO single‐nanowire transistor are 62 cm²/Vs, 10⁷, 155 μS/μm and 115 mV/dec, respectively. Practical use of such electrochemically‐gated field‐effect transistor (EG FET) devices is supported by their long‐term stability in air. Moreover, due to the good conductivity (≈10^?2 S/cm) of the CSPE, sufficiently high switching speed of such EG FETs is attainable; a cut‐off frequency in excess of 100 kHz is measured for in‐plane FETs with large gate‐channel distance of >10 μm. Consequently, operation speeds above MHz can be envisaged for top‐gate transistor geometries with insulator thicknesses of a few hundreds of nanometers. The solid polymer electrolyte developed in this study has great potential in future device fabrication using all‐solution processed and high throughput techniques.     

Solution‐Deposited Zinc Oxide and Zinc Oxide/Pentacene Bilayer Transistors: High Mobility n‐Channel,Ambipolar, and Nonvolatile Devices

A solution processed n‐channel zinc oxide (ZnO) field effect transistor (FET) was fabricated by simple dip coating and subsequent heat treatment of a zinc acetate film. The field effect mobility of electrons depends on ZnO grain size, controlled by changing the number of coatings and zinc acetate solution concentration. The highest electron mobility achieved by this method is 7.2 cm² V^?1 s^?1 with On/Off ratio of 70. This electron mobility is higher than for the most recently reported solution processed ZnO transistor. We also fabricated bilayer transistors where the first layer is ZnO, and the second layer is pentacene, a p‐channel organic which is deposited by thermal evaporation. By changing the ZnO grain size (or thickness) this type of bilayer transistor shows p‐channel, ambipolar and n‐channel behavior. For the ambipolar transistor, well balanced electron and hole mobilities are 7.6 × 10^?3 and 6.3 × 10^?3 cm² V^?1 s^?1 respectively. When the ZnO layer is very thin, the transistor shows p‐channel behavior with very high reversible hysteresis. The nonvolatile tuning function of this transistor was investigated.     

N‐Type Self‐Assembled Monolayer Field‐Effect Transistors and Complementary Inverters

This work describes n‐type self‐assembled monolayer field‐effect transistors (SAMFETs) based on a perylene derivative which is covalently fixed to an aluminum oxide dielectric via a phosphonic acid linker. N‐type SAMFETs spontaneously formed by a single layer of active molecules are demonstrated for transistor channel length up to 100 μm. Highly reproducible transistors with electron mobilities of 1.5 × 10^?3 cm² V^?1 s^?1 and on/off current ratios up to 10⁵ are obtained. By implementing n‐type and p‐type transistors in one device, a complimentary inverter based solely on SAMFETs is demonstrated for the first time.     

Air‐Stable n‐Type Organic Field‐Effect Transistors Based on Carbonyl‐Bridged Bithiazole Derivatives

An electronegative conjugated compound composed of a newly designed carbonyl‐bridged bithiazole unit and trifluoroacetyl terminal groups is synthesized as a candidate for air‐stable n‐type organic field‐effect transistor (OFET) materials. Cyclic voltammetry measurements reveal that carbonyl‐bridging contributes both to lowering the lowest unoccupied molecular orbital energy level and to stabilizing the anionic species. X‐ray crystallographic analysis of the compound shows a planar molecular geometry and a dense molecular packing, which is advantageous to electron transport. Through these appropriate electrochemical properties and structures for n‐type semiconductor materials, OFET devices based on this compound show electron mobilities as high as 0.06 cm² V^?1 s^?1 with on/off ratios of 10⁶ and threshold voltages of 20 V under vacuum conditions. Furthermore, these devices show the same order of electron mobility under ambient conditions.     

Programmed High‐Hole‐Mobility Supramolecular Polymers from Disk‐Shaped Molecules

In this paper a simple, casting solution technique for the preparation of two‐dimensional (2D) arrays of very‐high molecular weight (MW) 1D‐Pc supramolecular inorganic polymers is described. The soluble fluoroaluminium tetra‐tert‐butylphthalocyanine (ttbPcAlF) is synthesized and characterized, which can be self‐assembled to form 2D arrays of very‐high‐MW 1D‐Pc supramolecular inorganic polymers. High‐resolution transmission electron microscopy (HRTEM) demonstrates that the 1D‐ttbPcAlF, having a cofacial ring spacing of ～0.36 nm and an interchain distance of ～1.7 nm, self‐assembles into 2D‐nanosheets (～140 nm in length, ～20 nm in width, and equivalent to MW of 3.2 × 10⁵ g mol^?1). The film cast from a 1,2‐dichloroethane (DCE) solution shows a minimum hole‐mobility of ～0.3 cm² V^?1 s^?1 at room temperature by flash‐photolysis time‐resolved microwave conductivity (TRMC) measurements and a fairly high dark dc‐conductivity of ～1 × 10^?3 S cm^?1.     

An Integrated Free‐Standing Flexible Electrode with Holey‐Structured 2D Bimetallic Phosphide Nanosheets for Sodium‐Ion Batteries

An integrated, free‐standing, and binder‐free type of flexible anode electrode is fabricated from numerous holey‐structured, 2D nickel‐based phosphide nanosheets connected with carbon nanotubes. This electrode architecture can not only uniformly disperse the nanosheets throughout the whole electrode to avoid aggregation or detachment, but also provide an ideal sodium ion and electrolyte diffusion and penetration network with high electronic conductivity. Meanwhile, bimetallic phosphide formation by introducing secondary metal species will lead to a synergistic effect to modify the electrochemical properties. Due to the excellent compositional and structural characteristics of this electrode, it delivers superior performance. This designed flexible anode with Ni_1.5Co_0.5P_x nanosheets demonstrates a reversible capacity of 496.4 mAh g^?1 at 0.5 C and a good rate capacity of 276.1 mAh g^?1 at 8 C. Meanwhile, this connected integrated network woven from carbon nanotubes can effectively restrain volumetric expansion and shrinkage, and affect the conversion reaction products formation as well, from large‐sized microspheres to film structure, which is primarily credited with the improvement in electrochemical performance. This work may open up a new path for the synthesis of morphology‐controlled phosphides and promote the further development of flexible devices.     

Electrolyte‐Gated n‐Type Transistors Produced from Aqueous Inks of WS2 Nanosheets

Solution‐processed, low cost thin films of layered semiconductors such as transition metal dichalcogenides (TMDs) are potential candidates for future printed electronics. Here, n‐type electrolyte‐gated transistors (EGTs) based on porous WS₂ nanosheet networks as the semiconductor are demonstrated. The WS₂ nanosheets are liquid phase exfoliated to form aqueous/surfactant stabilized inks, and deposited at low temperatures (T < 120 °C) in ambient atmosphere by airbrushing. No solvent exchange, further additives, or complicated processing steps are required. While the EGTs are primarily n‐type (electron accumulation), some hole transport is also observable. The EGTs show current modulations > 10⁴ with low hysteresis, channel width‐normalized on‐conductances of up to 0.27 µS µm^?1 and estimated electron mobilities around 0.01 cm² V^?1 s^?1. In addition, the WS₂ nanosheet networks exhibit relatively high volumetric capacitance values of 30 F cm^?3. Charge transport within the network depends significantly on the applied lateral electric field and is thermally activated, which supports the notion that hopping between nanosheets is a major limiting factor for these networks and their future application.     

Printed and Electrochemically Gated,High‐Mobility,Inorganic Oxide Nanoparticle FETs and Their Suitability for High‐Frequency Applications

Solution‐processed or printed n‐channel field‐effect transistors (FETs) with high performance are not reported very often in the literature due to the scarcity of high‐mobility n‐type organic semiconductors. On the other hand, low‐temperature processed n‐channel metal oxide semiconductor (NMOS) transistors from electron conducting inorganic‐oxide nanoparticles show reduced‐performance and low mobility because of large channel roughness at the channel‐dielectric interface. Here, a method to produce ink‐jet printed high performance NMOS transistor devices using inorganic‐oxide nanoparticles as the transistor channel in combination with a 3D electrochemical gating (EG) via printed composite solid polymer electrolytes is presented. The printed FETs produced show a device mobility value in excess of 5 cm² V^?1 s^?1, even though the root mean square (RMS) roughness of the nanoparticulate channel exceeds 15 nm. Extensive studies on the frequency dependent polarizability of composite polymer electrolyte capacitors show that the maximum attainable speed in such printed, long channel transistors is not limited by the ionic conductivity of the electrolytes. Therefore, the approach of combining printable, high‐quality oxide nanoparticles and the composite solid polymer electrolytes, offers the possibility to fully utilize the large mobility of oxide semiconductors to build all‐printed and high‐speed devices. The high polarizability of printable polymer electrolytes brings down the drive voltages to ≤1 V, making such FETs well‐suited for low‐power, battery compatible circuitry.     

Design,Synthesis, and Versatile Processing of Indolo[3,2‐b]indole‐Based π‐Conjugated Molecules for High‐Performance Organic Field‐Effect Transistors

A series of indolo[3,2‐b]indole (IDID) derivatives comprising the core unit of N,N‐dihexyl‐IDID with different aromatic and aliphatic substituents at 2‐ and 7‐position are designed and synthesized to construct high‐performance organic semiconductors by different processing routes. Structure‐property relationship of the derivatives is comprehensively studied in terms of their photophysical, electrochemical, structural, and electrical characteristics. IDID derivatives are either evaporated in vacuum or dissolved in common organic solvents to ensure applicalbility in different processing routes toward outstanding p‐type semiconductor films. Among others, the excellently soluble compound 4H4TIDID (with 2‐ and 7‐substituents of 5‐hexyl‐2,2′‐bithiophene moiety, solubility >20 wt% in chloroform), shows the highest field‐effect hole mobility of 0.97 cm² V^?1 s^?1 in a device constructed by vacuum‐deposition and 0.18 cm² V^?1 s^?1 in device cosntructed by spin‐coating, respectively. The 2D grazing incidence X‐ray diffraction of 4H4TIDID films in both devices identically show the 2D molecular orientation favorable for the high transistor mobility.     

Diketopyrrolopyrrole‐Based Conjugated Polymers Synthesized via Direct Arylation Polycondensation for High Mobility Pure n‐Channel Organic Field‐Effect Transistors

High‐performance unipolar n‐type conjugated polymers (CPs) are critical for the development of organic electronics. In the current paper, four “weak donor–strong acceptor” n‐type CPs based on pyridine flanked diketopyrrolopyrrole (PyDPP), namely PPyDPP1‐4FBT, PPyDPP2‐4FBT, PPyDPP1‐4FTVT, and PPyDPP2‐4FTVT, are synthesized via direct arylation polycondensation by using 3,3′,4,4′‐tetrafluoro‐2,2′‐bithiophene (4FBT) or (E)‐1,2‐bis(3,4‐difluorothien‐2‐yl)ethene (4FTVT) as weak donor unit. All four polymers exhibit low‐lying highest occupied molecular orbital (≈ ?5.90 eV) and lowest unoccupied molecular orbital energy levels (≈ ?3.70 eV). Top‐gate/bottom‐contact organic field‐effect transistors based on all four polymers display unipolar n‐channel characteristics with electron mobility (µ_e) above 1 cm² V^?1 s^?1 in air, and presented linear |I_SD|^1/2 ?V_GS plots and weak dependence of the extracted moblity on gate voltage (V_GS), indicative of the reliability of the extracted mobility values. Importantly, the devices based on PPyDPP1‐4FBT and PPyDPP2‐4FBT show a pure unipolar n‐channel transistor behavior as revealed by the typical unipolar n‐channel output characteristics and clear off‐regimes in transfer characteristics. Attributed to its high crystallinity and favorable thin film morphology, PPyDPP2‐4FBT shows the highest µ_e of 2.45 cm² V^?1 s^?1, which is among the highest for unipolar n‐type CPs reported to date. This is also the first report for DPP based pure n‐type CPs with µ_e greater than 1 cm² V^?1 s^?1.     

High‐Performance,Low‐Operating‐Voltage Organic Field‐Effect Transistors with Low Pinch‐Off Voltages

Organic field‐effect transistors suffer from ultra‐high operating voltages in addition to their relative low mobility. A general approach to low‐operating‐voltage organic field‐effect transistors (OFETs) using donor/acceptor buffer layers is demonstrated. P‐type OFETs with acceptor molecule buffer layers show reduced operating voltages (from 60–100 V to 10–20 V), with mobility up to 0.19 cm² V^?1 s^?1 and an on/off ratio of 3 × 10⁶. The subthreshold slopes of the devices are greatly reduced from 5–12 V/decade to 1.68–3 V/decade. This favorable combination of properties means that such OFETs can be operated successfully at voltages below 20 V (|V_DS| ≤ 20 V, |V_GS| ≤ 20 V). This method also works for n‐type semiconductors. The reduced operating voltage and low pinch‐off voltage contribute to the improved ordering of the polycrystalline films, reduced grain boundary resistance, and steeper subthreshold slopes.     

Influence of Thiol Self‐Assembled Monolayer Processing on Bottom‐Contact Thin‐Film Transistors Based on n‐Type Organic Semiconductors

The performance of bottom‐contact thin‐film transistor (TFT) structures lags behind that of top‐contact structures owing to the far greater contact resistance. The major sources of the contact resistance in bottom‐contact TFTs are believed to reflect a combination of non‐optimal semiconductor growth morphology on the metallic contact surface and the limited available charge injection area versus top‐contact geometries. As a part of an effort to understand the sources of high charge injection barriers in n‐channel TFTs, the influence of thiol metal contact treatment on the molecular‐level structures of such interfaces is investigated using hexamethyldisilazane (HMDS)‐treated SiO₂ gate dielectrics. The focus is on the self‐assembled monolayer (SAM) contact surface treatment methods for bottom‐contact TFTs based on two archetypical n‐type semiconductors, α,ω‐diperfluorohexylquarterthiophene (DFH‐4T) and N,N′bis(n‐octyl)‐dicyanoperylene‐3,4:9,10‐bis(dicarboximide) (PDI‐8CN₂). TFT performance can be greatly enhanced, to the level of the top contact device performance in terms of mobility, on/off ratio, and contact resistance. To analyze the molecular‐level film structural changes arising from the contact surface treatment, surface morphologies are characterized by atomic force microscopy (AFM) and scanning tunneling microscopy (STM). The high‐resolution STM images show that the growth orientation of the semiconductor molecules at the gold/SAM/semiconductor interface preserves the molecular long axis orientation along the substrate normal. As a result, the film microstructure is well‐organized for charge transport in the interfacial region.     

Controllable Shifts in Threshold Voltage of Top‐Gate Polymer Field‐Effect Transistors for Applications in Organic Nano Floating Gate Memory

Organic field‐effect transistor (FET) memory is an emerging technology with the potential to realize light‐weight, low‐cost, flexible charge storage media. Here, solution‐processed poly[9,9‐dioctylfluorenyl‐2,7‐diyl]‐co‐(bithiophene)] (F8T2) nano floating gate memory (NFGM) with a top‐gate/bottom‐contact device configuration is reported. A reversible shift in the threshold voltage (V_Th) and reliable memory characteristics was achieved by the incorporation of thin Au nanoparticles (NPs) as charge storage sites for negative charges (electrons) at the interface between polystyrene and cross‐linked poly(4‐vinylphenol). The F8T2 NFGM showed relatively high field‐effect mobility (µ_FET) (0.02 cm² V^?1 s^?1) for an amorphous semiconducting polymer with a large memory window (ca. 30 V), a high on/off ratio (more than 10⁴) during writing and erasing with an operation voltage of 80 V of gate bias in a relatively short timescale (less than 1 s), and a retention time of a few hours. This top‐gated polymer NFGM could be used as an organic transistor memory element for organic flash memory.     

Nonvolatile Ferroelectric P(VDF‐TrFE) Memory Transistors Based on Inkjet‐Printed Organic Semiconductor

Nonvolatile ferroelectric poly(vinylidene fluoride‐co‐trifluoroethylene) memory based on an organic thin‐film transistor with inkjet‐printed dodecyl‐substituted thienylenevinylene‐thiophene copolymer (PC12TV12T) as the active layer is developed. The memory window is 4.5 V with a gate voltage sweep of ?12.5 V to 12.5 V. The field effect mobility, on/off ratio, and gate leakage current are 0.1 cm²/Vs, 10⁵, and 10^?10 A, respectively. Although the retention behaviors should be improved and optimized, the obtained characteristics are very promising for future flexible electronics.     

Solution Processable Fluorenyl Hexa‐peri‐hexabenzocoronenes in Organic Field‐Effect Transistors and Solar Cells

The organization of organic semiconductor molecules in the active layer of organic electronic devices has important consequences to overall device performance. This is due to the fact that molecular organization directly affects charge carrier mobility of the material. Organic field‐effect transistor (OFET) performance is driven by high charge carrier mobility while bulk heterojunction (BHJ) solar cells require balanced hole and electron transport. By investigating the properties and device performance of three structural variations of the fluorenyl hexa‐peri‐hexabenzocoronene (FHBC) material, the importance of molecular organization to device performance was highlighted. It is clear from ¹H NMR and 2D wide‐angle X‐ray scattering (2D WAXS) experiments that the sterically demanding 9,9‐dioctylfluorene groups are preventing π–π intermolecular contact in the hexakis‐substituted FHBC 4 . For bis‐substituted FHBC compounds 5 and 6 , π–π intermolecular contact was observed in solution and hexagonal columnar ordering was observed in solid state. Furthermore, in atomic force microscopy (AFM) experiments, nanoscale phase separation was observed in thin films of FHBC and [6,6]‐phenyl‐C61‐butyric acid methyl ester (PC₆₁BM) blends. The differences in molecular and bulk structural features were found to correlate with OFET and BHJ solar cell performance. Poor OFET and BHJ solar cells devices were obtained for FHBC compound 4 while compounds 5 and 6 gave excellent devices. In particular, the field‐effect mobility of FHBC 6 , deposited by spin‐casting, reached 2.8 × 10^?3 cm² V^?1 s and a power conversion efficiency of 1.5% was recorded for the BHJ solar cell containing FHBC 6 and PC₆₁BM.