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In this study, the design, fabrication and detailed analysis of semi-transparent bifacial organic solar cells (ST-OSC) based on MoO3/Ag/WO3 (10/dm/dod nm) dielectric/metal/dielectric (DMD) transparent contact system integrated with PTB7 polymer were investigated. The study emphasizes the importance of designing transparent contact systems to optimize the solar cells' transparency (average visible transmittance, AVT), color rendering (color rendering index, CRI), efficiency (power conversion efficiency, PCE), and bifaciality. The performance of three distinct configurations was examined in the AVTmax (47.14% AVT, 3.93% PCE), (CRIext)max (23.82% AVT, 6.21% PCE), and Extreme Color (26.34% AVT, 5.81% PCE). The theoretically predicted AVTs for these configurations were 48.75%, 22.29%, and 25.15%, respectively. The strong agreement between theoretical and observed outcomes confirmed the accuracy of the Transfer Matrix Model (TMM). Furthermore, the assessment of bifaciality performance exhibited that the AVTmax had a bifaciality factor of 0.94, with a PCE of 3.67% under top illumination and 3.93% under bottom illumination. The high bifaciality of the structure designed with TMM to maximize the AVT demonstrates the value of calculations prior to solar cell structure fabricating and the possibility of constructing high bifaciality structures using this technique. [ABSTRACT FROM AUTHOR]

Abstract In this study, the design, fabrication and detailed analysis of semi-transparent bifacial organic solar cells (ST-OSC) based on MoO3/Ag/WO3 (10/dm/dod nm) dielectric/metal/dielectric (DMD) transparent contact system integrated with PTB7 polymer were investigated. The study emphasizes the importance of designing transparent contact systems to optimize the solar cells’ transparency (average visible transmittance, AVT), color rendering (color rendering index, CRI), efficiency (power conversion efficiency, PCE), and bifaciality. The performance of three distinct configurations was examined in the AVTmax (47.14% AVT, 3.93% PCE), (CRIext)max (23.82% AVT, 6.21% PCE), and Extreme Color (26.34% AVT, 5.81% PCE). The theoretically predicted AVTs for these configurations were 48.75%, 22.29%, and 25.15%, respectively. The strong agreement between theoretical and observed outcomes confirmed the accuracy of the Transfer Matrix Model (TMM). Furthermore, the assessment of bifaciality performance exhibited that the AVTmax had a bifaciality factor of 0.94, with a PCE of 3.67% under top illumination and 3.93% under bottom illumination. The high bifaciality of the structure designed with TMM to maximize the AVT demonstrates the value of calculations prior to solar cell structure fabricating and the possibility of constructing high bifaciality structures using this technique.

Organic solar cells are becoming a point of interest for researchers because they are less polluting than available solar cells in the photovoltaics industry. In this present work, we have optimized the characteristic parameters of the PTB7:PC71BM active layer along with graphene oxide (GO) as the hole transport layer (HTL) and PFN:Br as an electron transport layer (ETL) in the proposed organic solar cell. By optimizing the electron affinity (χActive) of the active layer, we observed the highest cell power conversion efficiency (PCE) of about 15.31% at χ Active = 3.9 eV , and we analyzed the active layer thickness-dependent optical properties. Further, the simultaneous effects of electron and hole mobility of the ETL and the HTL were examined. In addition, the impact of series and shunt resistance was observed within the practical range (0–10 Ω cm2) and (1 × 102 − 1 × 1010 Ω cm2), respectively. The obtained result shows that the cell performance is best for the lowest series resistance with shunt resistance of about 1 × 103 Ω cm2. The obtained fill factor is about 55%, which decreases rapidly with the increase in shunt resistance. Furthermore, the influence of environmental conditions, such as weather temperature and illumination intensity of the sunlight, have been monitored. In this context, the intensity of the sun is varied from 1 Sun to 5 Sun with a temperature variation from 253 K to 333 K, and it is found that the proposed organic cell provides the best output in its class at 1.5 Sun and 333 K. Altogether, the results signify that the overall efficiency of the proposed organic solar cell considering the best values of all parameters is 13.21%. [ABSTRACT FROM AUTHOR]

Despite the relatively high efficiency of the organic solar cells (OSCs), their stability issues have not yet been fully resolved. Various approaches have been reported in the literature to improve the overall performance and stability of OSCs. In this work, the approach of hot-substrate coating was carried out to enhance the performance and stability of OSCs based on the PTB7:PC71BM active layer. The approach involves maintaining the substrate temperature at 150°C, while depositing the active layers with a spin coater. The results demonstrate that OSCs fabricated via hot-substrate coating achieved a power conversion efficiency (PCE) of 7.94%, whereas devices with active layers deposited at room temperature (RT) achieved an average efficiency of 5.6%. According to the stability study of the devices, it was observed that the hot-substrate coated devices maintained 94% of their initial PCE after 72 h of operation. This is where the RT-coated devices retained 53% of their efficiency. In conclusion, the proposed approach can be applied to improve the efficiency and stability of organic solar cells. [ABSTRACT FROM AUTHOR]

• Thermal annealing of PTB7:PC 71 BM blend with and without DIO additive is studied. • For, PTB7:PC 71 BM:DIO devices, the efficiency is improved by 25% at 40 °C and decreased for 60–80 °C. • DIO free blend: PCE is found to be independent with annealing temperatures. • Unfavorable distribution of PTB7 and PC 71 BM has been suggested for with DIO films at 80 °C. 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 acid methyl ester (PC 71 BM) (PTB7:PC 71 BM) 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 (J sc)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 J sc 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. [ABSTRACT FROM AUTHOR]

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.

Abstract Erbium (III) tris(8-hydroxyquinoline) ErQ complex is emerging as a class of novel luminescent material for interfacial engineering to improve the performance of organic solar cells (OSCs). In the present work, ErQ doped ZnO solution has successfully been prepared by the sol-gel route at room temperature as an electron transport layer for high efficient OSCs. The modified ErQ:ZnO films can yield not only higher electron mobility, good surface quality by the passivation of ZnO defects, but also slightly higher work-function and thereby shortening in the leakage current, which subsequently enhanced power conversion efficiency (PCE). As a result, the remarkable PCE increasing from 3.62% to 4.26% for poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester (P3HT:PC 61 BM) and from 6.84% to 7.95% for polymer thieno [3,4-b] thiophene/benzodithiophene: [6,6] phenyl-C 71 -butyric acid methyl ester (PTB7:PCB 71 M) devices could be achieved upon an incorporating ErQ:ZnO interfacial layer. Graphical abstract Image 1 Highlights • Sol-gel derived ErQ films can be served as an electron transport layer. • Optimization, structural, optical and morphological studies are discussed. • PCE of up to 4.26% for P3HT:PCBM and 7.95% for PTB7:PCBM solar cells. [ABSTRACT FROM AUTHOR]

Visualizing and controlling the phase separation of the donor and acceptor domains in organic bulk-hetero-junction (BHJ) solar devices made with poly([4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b’]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethyl-hexyl)carbon-yl]thieno[3,4-bthiophenediyl]) (PTB7) and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) are needed to achieve high power conversion efficiency (PCE). Traditional bright-field (BF) imaging, especially of polymeric materials, produces images of poor contrast when done at the nanoscale level. Clear nanoscale morphologies of the PTB7:PC71BM blends prepared with different 1,8-diiodooctane (DIO) concentrations were seen when using the energy-filtered transmission electron microscopy (EFTEM). The electron energy loss (EELS) spectra of the pure PTB7 and PC71BM samples are centered at 22.7 eV and 24.5 eV, respectively. Using the electrons whose energy losses are in the range of 16–30 eV, detail information of the phase morphology at the nanoscale was obtained. Correlations between the improvement in the photovoltaic performances and the increased electron mobility were seen. These correlations are discussed in terms of the changes (at the nanoscale level) in blending phase morphology when different DIO concentrations are added. [ABSTRACT FROM AUTHOR]

Since a large amount of solvents are needed for roll-to-roll printing processes of organic photovoltaic cells, an environmentally friendly process for practical mass production systems is in high demand. In this research, a highly efficient organic photovoltaic cell was successfully demonstrated by the electrospray deposition method using a non-halogenated solvent, o-xylene. An addition of acetonitrile and 1,8-diiodooctane drastically reduced domain size of the organic active layer, resulting in improved device performance. In addition, the photoconversion efficiency was continuously increased with increasing the solvent evaporation time of a droplet deposited on a substrate, and the highest photoconversion efficiency of 5.6% was achieved by optimizing the solvent evaporation time. Current-density-voltage characteristics under irradiation with AM 1.5 light and corresponding AFM images of the active layers electrosprayed with and without the addition of 1,8-diiodooctane in o-xylene and acetonitrile. [ABSTRACT FROM AUTHOR]

The impact of alkyl chain length of different additives, such as 1,4-diiodobutane (DIB), 1,6-diiodohexane (DIH), 1,8-diiodooctane (DIO) and 1,10-diiododecane (DID), on the PC 71 BM distribution in PTB7:PC 71 BM-based polymer solar cells, is systematically investigated, for the first time. Among these additives, DIO is found to have the optimum alkyl chain length that maximizes the performance of PTB7:PC 71 BM based polymer solar cells, attaining a power conversion efficiency as high as 8.84%, which is almost four times higher than that without any additives. For DID additives (longer alkyl chain length than DIO), a drop in efficiency to 7.91% was observed. Experimental investigations show that the microstructure of the bulk and the surface layer as well as the surface morphology of the PTB7:PC 71 BM polymer film can be controlled simultaneously by varying the alkyl chain length of additives. Results also show that the substantial improvement in performance is attributed to the improved 1) phase segregation, 2) PC 71 BM distribution uniformity in the bulk of the PTB7:PC 71 BM film, 3) surface smoothness and 4) high PTB7 content at the interface between the active layer and the top electrode. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The nanoscale morphology of polymer blends is a key parameter to reach high efficiency in bulk heterojunction solar cells. Thereby, research typically focusing on optimal blend morphologies while studying nonoptimized blends may give insight into blend designs that can prove more robust against morphology defects. Here, we focus on the direct correlation of morphology and device performance of thieno[3,4- b ]-thiophene- alt -benzodithiophene (PTB7):[6,6]phenyl C 71 butyric acid methyl ester (PC 71 BM) bulk heterojunction (BHJ) blends processed without additives in different donor/acceptor weight ratios. We show that while blends of a 1:1.5 ratio are composed of large donor-enriched and fullerene domains beyond the exciton diffusion length, reducing the ratio below 1:0.5 leads to blends composed purely of polymer-enriched domains. Importantly, the photocurrent density in such blends can reach values between 45 and 60% of those reached for fully optimized blends using additives. We provide here direct visual evidence that fullerenes in the donor-enriched domains are not distributed homogeneously but fluctuate locally. To this end, we performed compositional nanoscale morphology analysis of the blend using spectroscopic imaging of low-energy-loss electrons using a transmission electron microscope. Charge transport measurement in combination with molecular dynamics simulations shows that the fullerene substructures inside the polymer phase generate efficient electron transport in the polymer-enriched phase. Furthermore, we show that the formation of densely packed regions of fullerene inside the polymer phase is driven by the PTB7:PC 71 BM enthalpy of mixing. The occurrence of such a nanoscale network of fullerene clusters leads to a reduction of electron trap states and thus efficient extraction of photocurrent inside the polymer domain. Suitable tuning of the polymer-acceptor interaction can thus introduce acceptor subnetworks in polymer-enriched phases, improving the tolerance for high-efficiency BHJ toward morphological defects such as donor-enriched domains exceeding the exciton diffusion length.

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:PC 71 BM 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 (F 5 -rGO) was suspended in dimethylformamide for easy deposit by wet techniques such as spin-cast. F 5 -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 F 5 -rGO was 5.82%. An enhanced PCE of 7.67% when F 5 -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 (H 5 -rGO) was also obtained from GO treated with phenylhydrazine, and ternary OSCs were also prepared by adding H 5 -rGO to the PTB7:PC 71 BM blend at different weight ratios: 0, 3, and 6%. The best results were achieved with 3% of H 5 -rGO: OSCs presented a PCE of 7.56%. Image 1 • One-step functionalized-reduced graphene oxide used in organic solar cells (OSC). • Fluorinated reduced graphene oxide F 5 -rGO and F 5 -rGO/PEDOT:PSS as hole transport. • OSCs PTB7:PC 71 BM-based reached efficiencies of 5.82% and 7.67%, respectively. • Chemically reduced graphene oxide H 5 -GO as third component into the active layer. • OSCs efficiency about 7.56% with 3 wt% of H 5 -rGO in the active layer was reached. [ABSTRACT FROM AUTHOR]

Optimizing the function of interfacial materials between the photoactive layer and the metal cathode is critical for realizing high‐efficiency organic solar cells (OSCs). The charge‐collecting layer requires a material with an excellent electrical property to improve the charge collection efficiency and decrease the leakage current that increases the power conversion efficiency (PCE). In this study, the performance of sol–gel‐derived modified cathode interfacial (ZnO) layers, prepared by an appropriate doping of metal (M = Al, Ga, and Mn)quinoline (Q) groups in OSCs, is demonstrated and evaluated. The light absorption of the photoactive layer is improved upon incorporating an interfacial layer into the OSCs. The PCE of the GaQ:ZnO‐based device is higher than that of the AlQ:ZnO and MnQ:ZnO‐based devices, attributed to an improved exciton dissociation rate, enhanced carrier transport, greater electron mobility, and a lower work function. Incorporating a GaQ:ZnO interfacial layer into a thieno[3,4‐b]thiophene/benzodithiophene:[6,6]‐phenyl‐C71‐butyric acid methyl ester (PTB7:PC71BM) OSC increases the PCE from 7.51% to 8.44%, and incorporating it into a poly[[2,6′‐4‐8‐di(5‐ethylhexylthienyl)benzo[1,2‐b:3,3‐b]dithiophene][3‐fluoro‐2[(2‐ethylhexyl) carbonyl]thieno[3,4‐b]thiophenediyl:[6,6]‐phenyl‐C71‐butyric acid methyl ester (PTB7‐Th:PC71BM) (PTB7‐Th:PC71BM) OSC increases the PCE from 8.11% to 9.02%. The performance of ZnO interfacial layers doped with metal–quinoline (Q) groups is demonstrated in organic solar cells (OSCs). The light absorption of the photoactive layer is improved upon incorporating a doped interfacial layer into OSCs. The power conversion efficiency of OSC with GaQ:ZnO interfacial layer can be substantially increased attributed to an improved exciton dissociation rate, enhanced carrier transport, and a lower work function. [ABSTRACT FROM AUTHOR]