PCBM Solar Cells Research Articles

Spin effect in the ferromagnetic organic photovoltaics cells

In organic photovoltaic devices, the separation and transport of photogenerated charges play crucial roles for power conversion efficiency. Magnetic doping in organic solar cells can effectively enhance the power conversion efficiency by introducing a static magnetic field. In this study, we observed that in pure organic magnetic solar cells, the spin-polarization-induced spin scattering effect can also efficiently modulate the photocurrent in solar cells. Compared to the demagnetized state, the short-circuit current of PTB7:nw-P3HT:PCBM solar cells increased by approximately 0.3 % after magnetization. The dielectric constant only increased by about 0.05 %. However, above the Curie temperature 310 K, the long-range spin order in PTB7:nw-P3HT:PCBM solar cells disappears, resulting in consistent circuit currents before and after magnetization. Therefore, magnetic doping can enhance the short-circuit current in organic solar cells by weakening the spin scattering effect and enhancing the charge carrier mobility.

Advancements in P3HT:PCBM solar cells through experimental and simulated techniques

Organic solar cells are a promising alternative in photovoltaics due to their low manufacturing cost and flexibility. In this study, we developed an organic solar cell of structure (ITO/PEDOT:PSS/P3HT:PCBM/Al) where the active layer is represented by P3HT:PCBM. Experimental studies revealed that this layer has an energy gap of 1.9 eV and a good absorption coefficient of 3×105cm−1 . Using analytical and experimental methods based on (J–V–T) curves, we extracted the key parameters of our device, including parasitic resistances ( Rs and Rsh ), ideality factor (n), and Schottky potential barrier ( ϕB) at different temperatures. Also the charge transport mechanism in our junction is identified in this study. We then used simulation to evaluate the performance of our solar cell, obtaining an initial efficiency of 2.13%, in line with experimental results from other research. Our results confirm the feasibility of our theoretical approach, with performance consistent with previous work. However, by introducing an electron transport layer layer (PFN-Br or PDINO), we were able to improve efficiency up to 4.25%. These results highlight the importance of optimising intermediate layers to maximise the efficiency of organic solar cells.

(Invited) Interface Engineering for Organic and Perovskite Photovoltaics

Organic and perovskite solar cells have been intensively studied because they are considered as one of the most promising photovoltaic devices. Indeed, power conversion efficiencies (PCEs) have recently exceeded 19% for organic solar cells and 25% for perovskite solar cells. In both devices, interface engineering is highly important for efficient photovoltaic performance. In particular, it has great impact on open-circuit voltage (V OC) because charge carriers would recombine bimolecularly at the interface. In this talk, I will discuss how interface impact on V OC in polymer solar cells and perovskite solar cells.First, I will discuss how interfacial charge transfer (CT) states impact on V OC in polymer solar cells. More specifically, we employed two crystalline polymers (PTzBT-BOHD and PTzBT-12OD) and a fullerene derivative (PCBM). PTzBT-BOHD and PTzBT-12OD consist of the same backbone with different side chains: PTzBT-BOHD has two branched side chains of butyloctyl (BO) and hexyldecyl (HD) groups and PTzBT-12OD has a linear side chain of dodecyl (12) group and a branched side chain of octadecyl (OD) group. Interestingly, these PTzBT-BOHD/PCBM and PTzBT-12OD/PCBM solar cells exhibited different V OCs, although the two crystalline polymer neat films exhibit the same ionization energy because of the same backbone structure. In order to address the origin of the different V OCs, we carefully analyzed the interfacial CT state in the blend films. As a result, we found the interfacial CT state energy is higher in PTzBT-BOHD/PCBM than in PTzBT-12OD/PCBM blend films. This is because HOMO level of PTzBT-BOHD is deeper than that of PTzBT-12OD in disordered mixed phase in blend films, which results from twisted backbone of PTzBT-BOHD with branched side chains [1].Next, I will discuss how aging and passivation impact on interfacial energy matching and hence V OC in perovskite solar cells. As reported previously, V OC is often improved by ambient storage, which is called aging effect, and also improved by addition of passivation layers, which is called passivation effect. Such improvements in V OC suggest recombination would be suppressed effectively in these devices. Interestingly, V OC was gradually improved during ambient storage even for the passivated device where surface recombination is effectively suppressed by the passivation layer. By analyzing electronic properties of each layer, we found that no change was observed for the perovskite layer but the HOMO level deepening was observed for a hole-transporting material of spiro-OMeTAD during the ambient storage. As a result, energy matching between perovskite and spiro-OMeTAD layers was significantly improved and hence surface recombination was further effectively suppressed, resulting in the improvement in V OC [2,3].These findings clearly show that the electronic state at the interface critically impacts on V OC not only in polymer solar cells but also in perovskite solar cells, and therefore suggest that device design based on interface engineering is of particular importance for further improvement in V OC.

Simulation and Fabrication of P3HT:PCBM Solar Cell

Poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C71 butyric acid methyl ester (PCBM) polymer solar cell is studied by using GPVDM simulations and experiments. The research focuses on the effects of active layer thickness on solar cell structures as bulk heterojunction (BHJ) (ITO/P3HT:PCBM/Al) as compared to a bilayer structure (ITO/P3HT/PCBM/Al). The optimal active layer thickness of 200 nm is obtained in the simulation for BHJ solar structure. The results also indicate that bulk heterojunctions exhibit slightly higher efficiency than bilayer solar cell with the same thickness, possibly due to a better and worthier total surface region for charge separation and reduced recombination between the electrons and holes. BHJ solar cell is fabricated in the experiment by using spin coating. The results show that higher spin speeds result in a thinner active layer, and the device coated at 2500 rpm had the highest power conversion efficiency of 0.91 % because of a higher Isc and fill factor, despite a low absorption. The results suggest that bulk resistance, and morphology of the active layer play important roles in the carrier transport in the P3HT:PCBM solar cell.

Effects of Acceptors on the Charge Photogeneration Dynamics of PM6-Based Solar Cells

In this work, we investigated the effects of different acceptors (IT−4F and PC71BM) on the charge dynamics in PM6-based solar cells. The correlation between different acceptors and the performance of organic solar cells was studied by atomic force microscope, steady-state absorption spectrum, transient absorption spectrum, and electrical measurements. Optical absorption exhibited that IT−4F has strong absorption in the near-infrared region for the active layer. Transient absorption measurements showed that different acceptors (IT−4F and PC71BM) had a significant influence on the behaviors of PM6 excitons and charge dynamics. That is, the exciton dissociation rate and delocalized polaron transport in the PM6:IT−4F active layer were significantly faster than that in the PM6:PC71BM active layer. The lifetime of localized polaron in the PM6:PC71BM active layer was longer than that in the PM6:IT−4F active layer. Conversely, the lifetime of delocalized polaron in the PM6:IT−4F active layer was longer than that in the PM6:PC71BM active layer. Electrical measurement analysis indicated that lower bimolecular recombination, higher charge transport, and charge collection ability were shown in the PM6:IT−4F device compared with the PM6:PC71BM device. Therefore, PM6:IT−4F solar cells achieved a higher power conversion efficiency (12.82%) than PM6:PC71BM solar cells (8.78%).

Doping with Niobium Nanoparticles as an Approach to Increase the Power Conversion Efficiency of P3HT:PCBM Polymer Solar Cells.

Metal additive processing in polymer: fullerene bulk heterojunction systems is recognized as a viable way for improving polymer photovoltage performance. In this study, the effect of niobium (Nb) metal nanoparticles at concentrations of 2, 4, 6, and 8 mg/mL on poly(3-hexylthiophene-2,5-diyl) (P3HT)-6,6]-phenyl C61-butyric acid methyl ester (PCBM) blends was analyzed. The effect of Nb volume concentration on polymer crystallinity, optical properties, and surface structure of P3HT and PCBM, as well as the enhancement of the performance of P3HT:PC61BM solar cells, are investigated. Absorption of the P3HT:PC61BM mix is seen to have a high intensity and a red shift at 500 nm. The reduction in PL intensity with increasing Nb doping concentrations indicates an increase in PL quenching, suggesting that the domain size of P3HT or conjugation length increases. With a high Nb concentration, crystallinity, material composition, surface roughness, and phase separation are enhanced. Nb enhances PCBM's solubility in P3HT and decreases the size of amorphous P3HT domains. Based on the J-V characteristics and the optoelectronic study of the thin films, the improvement results from a decreased recombination current, changes in morphology and crystallinity, and an increase in the effective exciton lifespan. At high doping concentrations of Nb nanoparticles, the development of the short-circuit current (JSC) is associated with alterations in the crystalline structure of P3HT. The highest-performing glass/ITO/PEDOT:PSS/P3HT:PCBM:Nb/MoO3/Au structures have short-circuit current densities (JSC) of 16.86 mA/cm2, open-circuit voltages (VOC) of 466 mV, fill factors (FF) of 65.73%, and power conversion efficiency (µ) of 5.16%.

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.

Impact of phosphorescent dye on the performance and impedance spectroscopy for P3HT:PCBM solar cells

Impact of phosphorescent dye on the performance and impedance spectroscopy for P3HT:PCBM solar cells

The nature of excitons in PPDT2FBT:PCBM solar cells: Role played by PCBM

In organic semiconductor-based bulk heterojunction solar cells, the presence of an acceptor increases the formation of charge-transfer (CT) excitons, thereby leading to higher exciton dissociation probabilities. In this work we used steady-state electroabsorption (EA) measurements to probe the change in the nature of excitons as the blend composition of the solar cell active layer material was varied. We investigated blends of poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c]-[1,2,5]thiadiazole)] (PPDT2FBT) and (6,6)-phenyl C71 butyric acid methyl ester (PCBM). Analysis of the EA spectra showed that in the presence of a fullerene-based acceptor, like PCBM, CT characteristics of the excitons were modified, though no new CT signature was observed in the blend. Enhancement in the CT characteristics in the blend was reflected in photoluminescence (PL) measurements of the blends, where PL quenching of ∼63% was observed for 1% PCBM. The quenching reaches saturation at about 20% PCBM. However, efficiency of the device increased with a PCBM percentage beyond 20%. Maximum efficiency was obtained for the blend with 50% PCBM, among the blend compositions studied in this work, indicating the optimum concentration of PCBM for best power conversion efficiency to be around that value. When we compared the experimental results with simulations, the variation of the device efficiency with PCBM percentage was shown to arise from multiple factors, such as an increase in the polarizability and dipole moment of excitons, and the efficiency of the carrier collection from the bulk of the active layer.

Tetraaryldiamine-based electron-transporting interlayers for performance and stability enhancement of organic solar cells

Three novel tetraaryldiamines are synthesized and applied as an interlayer between zinc oxide (ZnO) and photoactive layers in PTB7-Th:PC71BM solar cells. The arylamines have an optical bandgap of 3.0–3.4 eV and do not interfere with the light-harvesting window of our polymer:fullerene combination. They enhance the power conversion efficiency from 7.48% in the control device to 8.95%, 8.18%, and 7.84% in PN-, PA-, and PAP-based devices, respectively. The dependence of photovoltaic parameters on the deposition conditions of the interlayer reveals that the current density and fill factor are the main parameters that increase when tetraaryldiamines are used as an interlayer. The external quantum efficiency increases from 73.1% in the bare ZnO device to 77.7–82.0% in the interlayer-incorporated devices. The power loss owing to the series and shunt resistances is reduced by a suitable alignment of the electronic energy levels with the interlayer and enhanced charge transfer through the components. Interlayer-incorporated devices also show a superior environmental stability compared to devices using bare ZnO. The results of this study should help advance the engineering strategies for organic solar cells with enhanced performances.

Optimizing the Photovoltaic Performance of Organic Solar Cells for Indoor Light Harvesting

Organic solar cells (OSCs) harvesting indoor light are highly promising for emerging technologies, such as internet of things. Herein, the photovoltaic performance of PTB7-Th:PC71 BM solar cells constructed using "optimized (with 1,8-diiodooctane (DIO))" and "non-optimized (without DIO)" processing conditions are compared for indoor and outdoor applications. We find that in comparison to the "optimized" solar cell, the "non-optimized" solar cell is less efficient under simulated solar light illumination (100 mW cm-2 , spectral range 350-1100 nm), owing to significant bimolecular charge carrier recombination losses. However, under simulated indoor illumination (3.28 mW cm-2 , spectral range 400-700 nm), bimolecular recombination losses are effective suppressed, thus the power conversion efficiency of the solar cell without DIO was increased to 14.7 %, higher than that of the solar cell with DIO (14.2 %). These results suggest that the common strategy used to optimize the OSCs could be undesired for indoor OSCs. We demonstrate that the efforts for realizing the desired "morphology" of the active layer for the outdoor OSCs may be unnecessary for indoor OSCs, allowing us to realize high-efficiency indoor OSCs using a non-halogenated solvent.

Organic bulk heterojunction solar cells spin-coated in ambient environment on flexible and glass substrates

Organic solar cells based on Poly (3-hexylthiophene) [6,6]-phenyl C61-butyric acid methyl ester (P3HT-PCBM) were fabricated in standard architecture by spin-coating on glass and on flexible polyethylene terephthalate (PET) substrates in ambient laboratory environment. In addition to the conventional DC characterization, impedance spectroscopy was used in order to study the capacitive behavior of the devices and obtain their electrical parameters. In combination with the electrical characterization methods, laser-beam-induced current (LBIC) measurements were used as a non-destructive method of mapping the photocurrent distribution and analyzing local device failures and macroscopic defects (shunts, dark spots, defects). The results of the study can be used to develop guidelines for the development and design of P3HT:PCBM solar cells in ambient environment.

Charge Photogeneration and Recombination in Fluorine-Substituted Polymer Solar Cells.

In this contribution, we studied the effect of fluorine substitution on photogenerated charge generation, transport, and recombination in polymer solar cells. Two conjugated polymer materials, PBDTTT-E (fluorine free) and PTB7 (one fluorine substitution), were compared thoroughly. Meanwhile, various characterization techniques, including atomic force microscopy, steady-state spectroscopy, transient absorption spectroscopy, spectroelectrochemistry, and electrical measurements, were employed to analyse the correlation between molecular structure and device performance. The results showed that the influence of fluorine substitution on both the exciton binding energy of the polymer and the carrier recombination dynamics in the ultrafast timescale on the polymer was weak. However, we found that the fluorine substitution could enhance the exciton lifetime in neat polymer film, and it also could increase the mobility of photogenerated charge. Moreover, it was found that the SOMO energy level distribution of the donor in a PTB7:PC71BM solar cell could facilitate hole transport from the donor/acceptor interface to the inner of the donor phase, showing a better advantage than the PBDTTT-E:PC71BM solar cell. Therefore, fluorine substitution played a critical role for high-efficiency polymer solar cells.

Magneto-electrical properties of nickel phthalocyanine thin film and its application in organic solar cells

The nickel phthalocyanine (NiPc) thin film has been explored for magneto-conductance and optoelectrical properties. The surface morphology and the opto-electrical properties of thin films of NiPc have been observed as a good candidate for the applications in polymer solar cells. The AFM images show an almost continuous surface over the studied area. The spin interaction, the disordering of the spins part, and their suitable models have been discussed by the magneto-conductance properties of the thin films. The relaxation time of carriers and traps filling phenomena with applied bias are discussed by the impedance spectroscopy. The thin films of NiPc have been introduced as a hole interface buffer layer in the standard structure of P3HT: PCBM solar cells. The power conversion efficiency (PCE) of the optimized solar cell with NiPc is ∼3.17% and the fill factor (FF) is ∼69%., these device parameters are higher (PCE increased by ∼65% and FF by ∼39%) as compared to the organic solar cells fabricated without NiPc thin films in the same batch. The improved performance of organic solar cells attributed due to lowering the series and shunt resistance.

Investigation of the performance parameters of P3HT: PCBM solar cell: The role of temperature

The temperature dependence of solar cells is a fundamental problem determines the device performance at unstable operating and environmental conditions. In this paper considering the temperature dependence of practical parameters, we have used an analytical drift-diffusion model to calculate the characteristic parameters of solar cell. We applied the Modified Tauc-lorentz temperature dependent model to describe the dielectric function of active layer, in order to study the performance of an organic P3HT: PCBM solar cell at different temperatures. Solving the steady-state continuity equation for electrons and holes regarding the dissociation probability of Onsager Braun along with bimolecular recombination rate, we have calculated the carrier’s concentration in P3HT: PCBM organic active layer. The absorption coefficient and its temperature dependence is compared with the results of similar experimental data.

Bimetallic core-shell nanoparticles to improve the absorption of P3HT: PCBM organic solar cell.

In this paper, we have theoretically studied a poly (3-hexylthiophene): 6,6-phenyl C61-butyric acid methyl ester (P3HT: PCBM) organic solar cell with randomly dispersed bimetallic nanoparticles. We have considered bimetallic core-shell Ag-Au nanoparticles as scattering centers randomly distributed among the active layer of a P3HT: PCBM solar cell. To study the role of Ag-Au nanoparticles, we have used the effective medium theory. The extinction and scattering cross sections of core-shells have been calculated based on the extended Mie theory. The scattering cross section of the active layer has been calculated by combining the extended Mie theory with the effective medium theory. The calculated current-voltage curve of solar cells has been compared with the experimental data of similar works to check the model's validity. In the optimized situation, it shows good agreement with experimental data, and we have obtained about 59% enhancement in the short circuit current of the solar cell.

Understanding of Photophysical Processes in DIO Additive-Treated PTB7:PC71BM Solar Cells

1,8-diiodooctane (DIO) additive is an important method for optimizing the morphology and device performance of polythieno[3,4-b]-thiophene-co-benzodithiophene (PTB7)-based polymer solar cells. However, the effect of DIO additive on charge photogeneration dynamics of PTB7-based polymer solar cells is still poorly understood. In this work, the effect of DIO additive on the carrier photogeneration dynamics, as well as device performance of PTB7: [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) solar cells was studied. Bias-dependent photoluminescence (PL) experiments of a neat PTB7 device show that the exciton cannot be dissociated by the electric field in the device within the operating voltage range, but it can be effectively dissociated by the high electric field. PL and time-resolved PL studies show that DIO additive reduces the phase size of PTB7 in the blend film, resulting in an increased exciton dissociation efficiency. The carrier recombination processes were studied by transient absorption, which shows geminate carrier recombination was suppressed in the DIO-treated PTB7:PC71BM device in ultrafast time scale. The increased exciton dissociation efficiency and suppressed carrier recombination in ultrafast time scale play an important role for DIO-treated PTB7:PC71BM solar cells to attain a higher power conversion efficiency.

Unraveling the Instability Issues in P3HT:PCBM Solar Cells by Graphene/Carbon Quantum Dots and Host Polymer Chain/Fiber Arrangements

Unraveling the Instability Issues in P3HT:PCBM Solar Cells by Graphene/Carbon Quantum Dots and Host Polymer Chain/Fiber Arrangements

Organic Thin‐film Solar Cells Using Benzotrithiophene Derivatives Bearing Acceptor Units as Non‐Fullerene Acceptors

AbstractNew star‐shaped non‐fullerene acceptors (5Z,5′Z,5′′Z)‐5,5′,5′′‐((benzo[1,2‐b : 3,4‐b′ : 5,6‐b′′]trithiophene‐2,5,8‐triyltris(4‐octylthiophene‐5,2‐diyl))tris(methaneylylidene))tris(3‐octyl‐2‐thioxothiazolidin‐4‐one) (1: BTT‐OT‐ORD) and 2,2′,2′′‐((5Z,5′Z,5′′Z)‐((benzo[1,2‐b : 3,4‐b′ : 5,6‐b′′]trithiophene‐2,5,8‐triyltris(4‐octylthiophene‐5,2‐diyl))tris(methaneylylidene))tris(3‐octyl‐4‐oxothiazolidine‐5,2‐diylidene))trimalononitrile (2: BTT‐OT‐OTZDM) with a benzotrithiophene core, alkyl‐thiophen units, and acceptor units were designed and synthesized. The HOMO‐LUMO levels of 1 and 2 were determined by photoemission spectroscopy and UV‐Vis absorption spectroscopy. Binary blend and ternary blend bulk heterojunction (BHJ) organic solar cells with non‐fullerene acceptors 1 and 2 were fabricated with the inverted device structures of glass/ITO/ZnO/active_layer/MoO3/Ag. Both binary blend BHJ solar cells with 1 and 2 show lower JSC and larger VOC values than P3HT : PCBM solar cells. On the other hand, ternary blend BHJ organic solar cells, including 10 % of 1, exhibited a larger power conversion efficiency than P3HT : PCBM solar cells because the JSC value was largely improved.

Effect of thickness and temperature on flexible organic P3HT:PCBM solar cell performance

A blend of poly 3-hexylthiophene (P3HT) and [6, 6]-phenyl-C61-butyric acid methyl ester (PCBM) is used as a photoactive layer for simulating a bulk heterojunction organic solar using general-purpose photovoltaic device model (GPVDM) software. The optical and electrical performance of the cell had been analyzed by changing the thickness of each layer and substrate material over a range of operating temperatures from −10 °C to – 40 °C. The flexible device exhibits higher PCE compared to a rigid device. The performance of the device was studied using transient simulation at different operating temperatures showing degradation in overall performance while enhancing the de-trapping of charge carrier and the recombination rate. Despite the increase in the number of absorbed photons while increasing the active layer thickness to 300 nm, a successful conversion of photon energy to electrical energy is not possible at higher thickness. The electrical simulation showed that a maximum power conversion efficiency (PCE) can be achieved with 220 nm thick active layer while decreasing the thickness of ITO and PEDOT: PSS layers due to minimization of optical losses.