PCBM Organic Solar Cells Research Articles

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

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

Improved efficiency of polymer solar cells using alcohol-soluble self-doped N-type polymers as cathode interface layer

Extensive research has been conducted on polymeric cathode interface substances, known for their self-doping features, for their application in organic solar cells (OSCs) to improve the ohmic interaction at the electrode with the active layer. In this paper, two novel polymers, PIIDN-F and PIIDN-FN, with self-doping effect, were successfully synthesized by combining isoindigo (IID), which contains an amino side chain, as an electrons-deficient group with fluorene, which contains different side chains. A thorough examination was conducted on the self-doping properties, electrical conductivity, work efficiency, and the angle of water contact between the two substances. Following this, PIIDN-F and PIIDN-FN were effectively utilized as cathode interface layers (CILs) within PTB7-Th:PC71BM OSCs. The PIIDN-F and PIIDN-FN achieve power conversion efficiencies (PCEs) of 8.97% and 9.04%, respectively. Findings indicate that the quantity of polar groups significantly influences the polymer's conductivity, adjustable work function, and the interaction at interfaces. These results show that by simply adjusting the number of polar groups, it is possible to provide efficient CILs for high-performance OSCs.

THE OPTIMIZATION OF P3HT:PCBM THIN FILM THICKNESS FOR ORGANIC SOLAR CELLS

This study presents the complex relationship between film thickness and the properties of P3HT:PCBM thin films, looking at how different thicknesses affected their structural and optical properties. Poly(3, hexylthiophene) (P3HT) and poly(3, hexylthiophene) (PCMB) were blended in a 0.6:1 ratio and deposited using spin coating techniques. The research involve investigating the resulting changes in surface topography, optical properties, and electrical behaviour by systematically adjusting the film thickness through multiple coating repetitions ranging from one to three repetitions. Profilometric analysis revealed a direct relationship between film thickness and surface roughness, highlighting the importance of thickness in interfacial interactions within solar cells. Optical studies revealed fascinating trends in absorbance, transmittance, absorption coefficient, and extinction coefficient, highlighting the films' behaviour at various wavelengths. Surprisingly, regardless of thickness, the optical band gap remained constant, providing valuable insights for optimizing photon energy conversion. Measurements of the Hall effect revealed the effect of thickness on carrier mobility, concentration, conductivity, resistivity, and Hall voltage. Thinner films had higher mobility but lower carrier concentration, revealing a delicate balance critical for optimizing charge transport. The comprehensive analysis of the study sheds light on the complex interplay between film thickness and various properties, providing useful guidance for designing efficient P3HT:PCBM organic solar cells. This study's findings highlight the importance of precise control over film dimensions in improving the performance and efficiency of organic photovoltaic devices. This investigation paves the way for tailored approaches in the fabrication of next-generation organic solar cells, pushing the limits of renewable energy technology.

A numerical study on the relationship between the doping and performance in P3HT:PCBM organic bulk heterojunction solar cells

In this study, we perform a simulation analysis to investigate the influence of p-type and n-type doping concentration in BHJ SCs using the drift-diffusion model. Specifically, we investigate the effect of doping on the charge carrier transport and calculate the above-mentioned device parameters. We show that doping the active layer can increase the cell characteristic parameters, that the results are in an excellent agreement with the experimental results previously reported in the literature. We also show that doping causes space charge effects which subsequently lead to redistribution of the internal electric field in the device. Our results reveal that higher doping levels lead to screening the electrical field in the P3HT:PCBM active region. This in turn forces the charge carrier transport to be solely dominated by the diffusion, consequently decreasing the performance of the device. We also show that doping of the active layer to an optimum level can effectively improve the charge transport. Moreover, we show that doping can create an Ohmic contact between the organic and cathode interface. Additionally, the charge carrier concentration profile shows that by increasing the dopant concentration, the J_{sc} can be improved remarkably. Upon doping the active layer, this indicates that illumination can simply reduce the series resistance in the device.

Evolutionary optimization of the short-circuit current enhancement in organic solar cells by nanostructured electrodes

Using a particle swarm optimization algorithm (a population-based stochastic optimization technique) combined with 3D finite-difference time-domain simulations, we inverse design periodic arrays of metallic nanoparticles on indium-tin-oxide electrodes and nanoholes in metallic thin films working as electrodes in P3HT (Poly(3-hexylthiophene-2,5-diyl)):PCBM ([6,6]-Phenyl C61 butyric acid methyl ester) organic solar cells to achieve the maximum short-circuit currents (Jsc). Nanohole-array electrodes have large optical losses, leading to a net reduction of Jsc compared to a reference solar cell. On the other hand, nanoparticle arrays can lead to a significant enhancement of Jsc of up to 20%. Detailed simulations show that this enhancement is caused by the grating coupling of the incident light to surface plasmon polaritons at the interface of the metal electrode and the hole transport layer, leading to the enhancement of the electromagnetic field in the organic blend.

Importance of Electric-Field-Independent Mobilities in Thick-Film Organic Solar Cells.

In organic solar cells (OSCs), a thick active layer usually yields a higher photocurrent with broader optical absorption than a thin active layer. In fact, a ∼300 nm thick active layer is more compatible with large-area processing methods and theoretically should be a better spot for efficiency optimization. However, the bottleneck of developing high-efficiency thick-film OSCs is the loss in fill factor (FF). The origin of the FF loss is not clearly understood, and there a direct method to identify photoactive materials for high-efficiency thick-film OSCs is lacking. Here, we demonstrate that the mobility field-dependent coefficient is an important parameter directly determining the FF loss in thick-film OSCs. Simulation results based on the drift-diffusion model reveal that a mobility field-dependent coefficient smaller than 10-3 (V/cm)-1/2 is required to maintain a good FF in thick-film devices. To confirm our simulation results, we studied the performance of two ternary bulk heterojunction (BHJ) blends, PTQ10:N3:PC71BM and PM6:N3:PC71BM. We found that the PTQ10 blend film has weaker field-dependent mobilities, giving rise to a more balanced electron-hole transport at low fields. While both the PM6 blend and PTQ10 blend yield good performance in thin-film devices (∼100 nm), only the PTQ10 blend can retain a FF = 74% with an active layer thickness of up to 300 nm. Combining the benefits of a higher JSC in thick-film devices, we achieved a PCE of 16.8% in a 300 nm thick PTQ10:N3:PC71BM OSC. Such a high FF in the thick-film PTQ10 blend is also consistent with the observation of lower charge recombination from light-intensity-dependent measurements and lower energetic disorder observed in photothermal deflection spectroscopy.

Nanomorphology dependence of the environmental stability of organic solar cells

Previous studies have reported contradictory effects of small-molecule acceptors on the environmental stability of polymer:small-molecule blends, with one showing that a small-molecule acceptor stabilizes and another showing that it destabilizes the polymer donor. In this work, to investigate the origin of these contradictory results, the effects of the nanomorphologies of small-molecule acceptors on the environmental stability of polymer:small-molecule blends are demonstrated. Investigations on the environmental stabilities of polymer:fullerene blends of 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):phenyl-C61-butyric acid methyl ester (PCBM) with contrasting nanomorphologies of PCBM reveal that dispersed PCBM in a mixed phase is the critical factor that causes triplet-mediated singlet oxygen generation and, hence, the severe photooxidation of PTB7, whereas an aggregated PCBM phase stabilizes PTB7 by reducing the formation of PTB7 triplet excitons. In addition, the photooxidation of PTB7 substantially degrades hole transport in the PTB7:PCBM blends by destroying the crystalline PTB7 phases within the films; this effect is strongly correlated with the efficiency losses of the PTB7:PCBM organic solar cells. These conclusions are also extended to polymer:nonfullerene blends of PTB7:ITIC and PTB7:Y6, thereby confirming the generality of this phenomenon for polymer:small-molecule organic solar cells.

Scalable eDIPS-based single-walled carbon nanotube films for conductive transparent electrodes in organic solar cells

This letter demonstrates the scalable enhanced direct-injection pyrolytic synthesis (eDIPS)-based, wet-processed single-walled carbon nanotube (SWCNT) films for high-performance organic solar cells (OSCs) using acid dopants. Thanks to the good conductivity and smooth interfacial morphology of the 60 wt% HNO3-doped eDIPS-based SWCNT film, a power conversion efficiency (PCE) of 1.78% was achieved in a P3HT:PCBM OSC. In addition, the 60 wt% HNO3-doped eDIPS-based SWCNT film indicated excellent compatibility with a record-high PCE of 4.93% was achieved in a PBTZT-stat-BDTT-8:PCBM OSC.

Tin instead of aluminum as a back electrode in P3HT:PC71BM organic solar cells

In the present work, a thin film of Sn metal, instead of aluminum, was deposited as a back electrode, using thermal evaporation, for fabricating organic solar cells composed of poly(3-hexylthiophene) and [6,6]-phenyl-C71 butyric acid methyl ester. The effect of post-thermal annealing on performance parameters of the solar cell was investigated at low temperatures (suitable for organic solar cells) up to 180 °C. In addition, the effect of thermal annealing on morphological (using scanning electron microscopy) and electrical properties (using a Hall effect setup) of the Sn thin films is reported and discussed here. The obtained minor effect of thermal annealing on the morphological and electrical properties of the Sn thin films is offset by an improvement in the performance parameters of the solar cells after post-annealing at 160 °C. The present study shows good electrical properties of Sn thin films which are comparable with those of aluminum thin films.

Improved UV sensitivity and charge transport in PTB7-Th:PC71BM solar cells doped with cadmium selenide quantum dots

CdSe QDs are incorporated into PTB7-Th:PC71BM organic solar cells, which convert the ultraviolet light to visible light to improve the photon harvesting efficiency and gather on the top of active layers and enhance the electron transport capacity.

A comparative study of low-cost coating processes for green & sustainable organic solar cell active layer manufacturing

Owing to their facile integration into existing commercial products, high volume manufacturing of organic solar cells (OSCs) can be expected in the upcoming years. Therefore, it is important to evaluate the performance and sustainability of various active layer coating methods for OSCs. Herein, we compare four active layer coating processes: spin-coating, blade-coating, spray-coating and push-coating for poly(2,7-carbazole-alt-dithienylbenzothiadiazole):[6,6]-Phenyl-C71-butyric acid methyl ester (PCDTBT:PC71BM) active layers deposition. The optical, morphological and photovoltaic parameters of the active layers are studied. The suitability of each coating method for industrial manufacturing of PCDTBT:PC71BM OSCs is discussed in terms of environmental impact, necessary investments and running costs. Our results confirm that, despite producing high quality and high performance OSCs, spin-coating is unsuitable for high volume manufacturing due to the large amounts of materials and hazardous solvents wasted in the process. Blade-coating provides a good balance between low running costs, low environmental impact and decent performances but the process introduces lateral compositional gradients which could be detrimental for large area OSC processing. Spray-coating requires minimal initial investments but has relatively low performance and low manufacturing sustainability. Push-coating yields OSCs which perform as well as spin-coated ones, with a much lower environmental impact and cost. We should thus look forward to seeing whether this green and sustainable technology can develop into a large area coating process in the future.

Plasmonic Photocurrent Improvement in P3HT:PCBM Organic Solar Cells

The need to develop and deploy large-scale, cost-effective, renewable energy is becoming tremendously important in the last few decades. Nanostructured organic solar cells have the long-term potential to provide low cost, and high-efficiency renewable energy. In recent years, photovoltaic cells based on nanoparticles blended with semiconducting polymers have achieved good performance and distinguished power conversion efficiencies, greater than 17%. These structures include various sizes and shapes of metal nanoparticles. Intensive research is being done towards achieving organic solar cell efficiency of 20%. In this work, a detailed numerical simulation is done for a proposed nanostructured organic solar cell design. Different nanoparticle shapes and sizes are considered in the active layer (P3HT:PCBM) to obtain a highly efficient organic solar cell.

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.

Influence of ZnO nanoparticles as electron transport material on the performance and stability of organic solar cells with sputtered Ag back electrodes

ZnO has been widely used as electron selective material in P3HT:PCBM organic solar cells with either conventional or inverted architecture in order to enhance the extraction of electrons and block the collection of holes at one electrode. In this work we investigate the influence of ZnO nanoparticles electron transport layer (ETL) on the performance and stability of P3HT:PCBM based organic solar cells with conventional architecture and magnetron sputtered back Ag contacts. Their stability in the dark and under real outdoor conditions was monitored by current-voltage measurements and impedance spectroscopy. The impedance spectra were taken as a function of applied bias under illumination in order to reveal more information about the degradation mechanisms taking place in the device.

Inverted PTB7-Th:PC71BM organic solar cells with 11.8% PCE via incorporation of gold nanoparticles in ZnO electron transport layer

In bulk hetero-junction organic solar cells (BHJOSCs), light absorption can be improved by employing techniques such as plasmonic effects which can lead to improved device efficiencies. In this manuscript, we demonstrate highly efficient devices obtained upon incorporation of gold nanoparticles (Au NPs) of size 10–20 nm at various concentrations into solution processed ZnO (zinc oxide) electron transport layers (ETLs). The inverted OSC devices of configuration ITO/ZnO:Au NPs/PTB7-Th:PC71BM/MoO3/Ag show the highest power conversion efficiency (PCE) for an optimum concentration of Au NPs (0.05 wt%) in ZnO ETL layer driven by plasmonic effects leading to improved light absorption and improved interface between the active layer and the ETL leading to improved carrier collection. The effects together cause enhancement in the short circuit current density (Jsc) and fill factor (FF) leading to a maximum PCE of 11.8% with an open circuit voltage (Voc), short circuit current density (Jsc), and fill factor (FF) of 0.80 V, 21.75 mAcm−2, and ~68%, respectively. This PCE is 24% higher than the control device (ZnO ETL without Au NPs) and is among the best observed values for widely explored bulk hetero-junction (BHJ) solar cells based on PTB7-Th:PC71BM.

Role of DIO vis-à-vis microstructural kinetics during thermal annealing on the performance of PTB7:PC71BM organic solar cells

Thermal annealing is an important process to improve the power conversion efficiency (PCE) of bulk-hetero junction organic solar cells (BHJ OSCs) by inducing micro-structural changes within the active layer blend’s constituents leading to amelioration of charge transfer/transport dynamics and interfacial properties. This work investigates the impact of thermal annealing on the photovoltaic performance ofPoly[[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 acidmethyl ester(PC71BM) (PTB7:PC71BM) thin film blend in the presence of DIO (1,8 –Diiodooctane) additive, at different annealing temperatures (40, 60 and 80 °C) and correlates with the performance of DIO-free devices investigated under similar annealing conditions. Our results show that DIO-containing (w/DIO)blends, annealed at moderate temperature (40 °C) for 1 h exhibit significantly improved short circuit current (Jsc)as well as fill factor (FF) and hence 25% improvement in PCE over bench dried (unannealed) DIO-containing blend films. Interestingly, thermal treatment of DIO containing blend films at a higher temperature of 80 °C results in significant reduction of FF. However, for without DIO (w/o DIO) devices, FF remains unchanged while decrease in Jsc is significant. The inferior performance of both (w/DIO and w/o DIO) the devices at higher temperatures ~80 °C emanates from an unfavorable distribution of the polymer- fullerene network, as shown by morphological and surface potential analyses. Specifically, in w/DIO devices, the decreased performance is possibly induced by the temperature driven, accelerated loss of DIO additive that produces the evolution of undesirable morphology thus deteriorating the performance.

Abnormal dewetting of Ag layer on three-dimensional ITO branches to form spatial plasmonic nanoparticles for organic solar cells

Three-dimensional (3D) plasmonic structures have attracted great attention because abnormal wetting behavior of plasmonic nanoparticles (NPs) on 3D nanostructure can enhance the localized surface plasmons (LSPs). However, previous 3D plasmonic nanostructures inherently had weak plasmonic light absorption, low electrical conductivity, and optical transmittance. Here, we fabricated a novel 3D plasmonic nanostructure composed of Ag NPs as the metal for strong LSPs and 3D nano-branched indium tin oxide (ITO BRs) as a transparent and conductive framework. The Ag NPs formed on the ITO BRs have a more dewetted behavior than those formed on the ITO films. We experimentally investigated the reasons for the dewetting behavior of Ag NPs concerning the geometry of ITO BRs. The spherical Ag NPs are spatially separated and have high density, thereby resulting in strong LSPs. Finite-domain time-difference simulation evidenced that spatially-separated, high-density and spherical Ag NPs formed on ITO BRs dramatically boost the localized electric field in the active layer of organic solar cells (OSCs). Photocurrent of PTB7:PCBM OSCs with the ITO BRs/Ag NPs increased by 14%.

Comparative study of conventional and inverted P3HT: PCBM organic solar cell

This work is a comprehensive comparative study between conventional and inverted bulk hetero-junction (BHJ) Organic Solar Cell (OSC and IOSC) using GPVDM software. Contrary to conventional OSCs with a low work-function cathode located on the top, IOSC is characterized by a bottom transparent conductive oxide cathode. The calculated current-voltage characteristic (J-V) is used to extract the main electrical outputs (figures of merit) of the solar cell: the short circuit current (Jsc), the open circuit voltage (Voc), the fill factor (FF) and the efficiency (η). The effect of a number of physical parameters is studied including thickness of the different layers and materials used as electron (hole) transport layer, ETL (HTL). In addition, different top and bottom electrodes are suggested with mono and multi-thin layer. A comparison between the effect of all these factors in OSC and IOSC is also performed and it was found that IOSC using multi-thin layer ATZ (AZO/TiOx/ZnO) as bottom contact gives the best efficiency of 5.46% in comparison with 5.02% obtained for the conventional OSC with ZnO/TiOx/ZnO contact.

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.

Combined effect of ZnO nanoripples and solvent additive on the nanomorphology and performance of PTB7-Th: PC71BM organic solar cells

In bulk heterojunction organic solar cells (OSCs), nanomorphology of the photoactive layer plays a crucial role in determining photocurrent and fill factor (FF) of OSCs, and therefore it is essential to control the nanomorphology of the photoactive layer to fabricate devices with high power conversion efficiency (PCE). We demonstrate the combined effects of a ZnO nanorippled electron transport layer (ETL) and solvent additive (1,8-diiodooctane (DIO)) on the nanomorphology and performance of a model OSC in an inverted geometry. The photoactive layer in the model OSC is composed of 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] (PTB7-Th):phenyl-C71-butyric acid methyl ester (PC71BM) blend. It is observed that the use of ZnO nanoripples as an ETL and DIO as a solvent additive facilitates the formation of near ideal nanomorphology of bi-continuous interpenetrating network of donor and acceptor. This is confirmed by morphological studies using atomic force microscopy, scanning electron microscopy and transmission electron microscopy. Photo-electrochemical impedance spectroscopy measurements confirm that obtained nanomorphology of bicontinuous interpenetrating network is contributing to the improved device performance. The device with 3 vol% DIO, with underneath ZnO nanoripples exhibited improved current density (Jsc), FF, open circuit voltage (Voc) and PCE of 15.57 mA cm−2, 64.50%, 0.81V and 8.20%, respectively.