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Geminate recombination in organic photovoltaic blend PCDTBT/PC <sub/>71</sub> BM studied by out-of-phase electron spin echo spectroscopy
摘要： The key process in organic solar cell operation is charge separation under light illumination. Due to the low dielectric constant of organic materials, the Coulomb attraction energy within the interfacial charge-transfer state (CTS) is larger than the thermal energy. Understanding the mechanism of charge separation at the organic donor/acceptor interface still remains a challenge and requires knowledge of the CTS temporal evolution. To address this problem, the CTS in the benchmark photovoltaic blend PCDTBT/PC71BM was studied by the out-of-phase Electron Spin Echo (ESE). The protocol for determining the CTS geminate recombination rate for certain electron-hole distances was developed. Simulating the out-of-phase ESE trace for the CTS in the PCDTBT/PC71BM blend allows precise determination of the electron-hole distance distribution function and its evolution with the increase in the delay after the laser flash. Distances of charge separation up to 6 nm were detected upon thermalization at a temperature of 20 K. Assuming the exponential decay of the recombination rate, the attenuation factor β = 0.08 ??1 is estimated for the PCDTBT/PC71BM blend. Such a low attenuation factor is probably caused by a high degree of hole delocalization along the PCDTBT chain.
关键词： PCDTBT/PC71BM blend,electron spin echo,geminate recombination,organic solar cells,charge transfer state
更新于2025-09-23 15:19:57
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Graphene/TiO2 nanocomposite electrodes sensitized with tin sulfide quantum dots for energy issues
摘要： In this work, graphene (Gr)/TiO2 nanocomposite electrodes sensitized with tin sulfide quantum dots (SnS QDs) for energy issues have been investigated. Different sizes of SnS QDs as non-toxic and earth-abundant semi-conducting materials are synthesized onto Gr/TiO2 nanocomposite electrodes using successive ionic layer adsorption and reaction (SILAR) technique for “n” cycles (n: 1 to 8). The structural properties of the prepared SnS (n) QDs photoanodes are studied using an X-ray diffractometer. The XRD measurements ensure the formation of the crystalline structure of orthorhombic SnS QDs. The optical properties of the synthesized SnS(n) QDs photoanodes are characterized using a UV–visible spectrophotometer. The estimated direct (indirect) energy band gap (Eg) of the prepared SnS(n) photoanodes is tuned from 2.36 (1.57) eV to 1.76 (1.30) eV by controlling the number of SILAR cycles from 1 to 8. The photovoltaic performance of the assembled SnS(n) quantum dots sensitized solar cells (QDSSCs) has been studied under a solar power illumination of AM1.5 conditions. The optimal photovoltaic performance of the assembled SnS(n) QDSSCs is achieved at 6 SILAR deposition cycles. As compared with previous studies, enhancement of 48% in the energy conversion efficiency η has been achieved due to the active Gr incorporation. SnS(n) QDSSCs shows high reproducibility and sensitivity undercutting ON-OFF the solar illumination. Gr plays the role of kids slide for the photo-generated electrons and facilitates their transportation.
关键词： Graphene/TiO2,Reproducibility of QDSSCs,Recombination suppression,Tuning band gap,SnS solar Cell
更新于2025-09-23 15:19:57
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The effect of absorber thickness on the planar Sb2S3 thin film solar cell: Trade-off between light absorption and charge separation
摘要： Antimony sulfide Sb2S3 is an emerging photovoltaic absorber, which has been widely studied on synthesis route, device structure and interface. However, its device performance is still limited by the unoptimized Sb2S3 absorber and interface recombination, in which the neglected character of thickness is unclear. Here, the effect of absorber thickness on the Sb2S3 thin film solar cell was carefully investigated in the range of 80–620 nm, aiming to reveal the trade-off between charge separation and light absorption in the device. The characterization of JV and Sb2S3 thin film found that too thin Sb2S3 would lower the VOC and JSC, which was attributed to the severe shunt and insufficient absorption. While the too thick Sb2S3 would hinder the charge separation. This tendency was also confirmed by the performance simulation of device. Finally, the best power conversion efficiency of 4.96% is achieved with a 544 nm Sb2S3 absorber. This work provides the guidance to optimize the thickness of Sb2S3 absorber for solar cells.
关键词： Absorption,Recombination,Thickness,Solar cells,Sb2S3
更新于2025-09-23 15:19:57
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Extraction of the minority carrier transport properties of solar cells using the Hovel model and genetic algorithms
摘要： In this paper, a quick and accurate method for extraction of the minority carrier transport properties of p-n or n-p junction solar cells, such as diffusion lengths and surface recombination velocities, is presented. The knowledge of these parameters is essential to investigate factors that limit the performance of photovoltaic devices. The proposed method, based on genetic algorithms and the analytical Hovel model, is used to fit the external quantum efficiency (EQE) curves of solar cells with different emitter thicknesses. As a demonstrative example of application of the procedure carried out in this work, theoretical and experimental EQE curves of n-p GaAs solar cells under the standard AM1.5G spectrum have been used in order to extract the desired parameters. Errors less than 2.4% have been obtained, which shows the ability of the developed tool. An analysis of the total number of iterations is presented. Results obtained can be used to improve the design, optimization and manufacturing process of high efficiency photovoltaic devices.
关键词： diffusion length,surface recombination velocity,Hovel model and genetic algorithms,solar cells
更新于2025-09-23 15:19:57
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Transparent Electrode and Buffer Layer Combination for Reducing Carrier Recombination and Optical Loss Realizing over a 22%-Efficient Cd-Free Alkaline-Treated Cu(In,Ga)(S,Se) <sub/>2</sub> Solar Cell by the All-Dry Process
摘要： Structures of (K or Cs) alkaline-treated Cu(In,Ga)(S,Se)2 (CIGSSe) solar cells are developed, and their carrier recombination rates are scrutinized. It is determined that short-circuit current density (JSC) is enhanced (decreased optical loss), when ZnS(O,OH), (Cd,Zn)S, and Zn0.8Mg0.2O buffers with large band-gap energy (Eg) are applied as replacement of CdS buffer. The JSC is further increased, more reducing the optical loss, when Zn0.9Mg0.1O:B is used as transparent conductive oxide (TCO) with larger Eg and lower free carrier absorption than those of ZnO:Al. Furthermore, all carrier recombination rates throughout the devices with K or Cs treatment, especially at buffer/absorber interface and in quasi neutral region, are reduced, thereby reducing open-circuit voltage deficit (VOC,def), well consistent with the simulated ones. The carrier recombination rate at the buffer/absorber interface is further decreased, when the CdS and (Cd,Zn)S buffers, deposited by chemical bath deposition, are applied, leading to the more reduction of the VOC,def and the high conversion efficiency (η) of about 21%. Under the trade-off between VOC,def and optical loss, the highest η of 22.6% is attained with the lowest power loss (or the highest VOC × JSC) in the Cs-treated Cd-free CIGSSe solar cell with an optimized structure of glass/Mo/CIGSSe/Zn0.8Mg0.2O/Zn0.9Mg0.1O:B, fabricated by all-dry process, where the Zn0.8Mg0.2O buffer is prepared by the sputtering method. This occurs because the JSC is the highest attributable to the larger Eg of Zn0.8Mg0.2O buffer than those of the CdS and (Cd,Zn)S.
关键词： Zn1-xMgxO,Zn1-xMgxO:Al,Cu(In,Ga)(S,Se)2 thin-film solar cell,carrier recombination rates,Zn1-xMgxO:B,(Cd,Zn)S
更新于2025-09-23 15:19:57
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Suppressing Efficiency Roll-Off at High Current Densities for Ultra-Bright Green Perovskite Light-Emitting Diodes
摘要： Perovskite light-emitting diodes (PeLEDs) have undergone rapid development in the last several years with external quantum efficiencies (EQE) reaching over 21%. However, most PeLEDs still suffer from severe efficiency roll-off (droop) at high injection current densities, thus limiting their achievable brightness and presenting a challenge to their use in laser diode applications. In this work, we show that the roll-off characteristics of PeLEDs are affected by a combination of charge injection imbalance, nonradiative Auger recombination, and Joule heating. To realize ultrabright and efficient PeLEDs, several strategies have been applied. First, we designed an energy ladder to balance the electron and hole transport. Second, we optimized perovskite materials to possess reduced Auger recombination rates and improved carrier mobility. Third, we replaced glass substrates with sapphire substrates to better dissipate joule heat. Finally, by applying a current-focusing architecture, we achieved PeLEDs with a record luminance of 7.6 Mcd/m2. The devices can be operated at very high current densities (J) up to ~ 1 kA/cm2. Our work suggests a broad application prospect of perovskite materials for high-brightness LEDs and ultimately a potential for solution-processed electrically pumped laser diodes.
关键词： Joule heat,efficiency roll-off,Auger recombination,charge injection balance,high injection current density,ultrahigh brightness,perovskite light emitting diodes
更新于2025-09-23 15:19:57
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[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Equivalent Circuit For AC Response of Cu(In,Ga)Se <sub/>2</sub> Thin Film Solar Cells
摘要： Ultrathin Cu(In,Ga)Se2 (CIGS) is desired to reduce production costs of CIGS solar cells. The present work aims to study the AC electrical response of standard-thick, ultrathin and passivated ultrathin devices. Admittance measurements allow to choose the AC equivalent circuit for each type of CIGS device. It is of utmost importance to understand the AC electrical behavior of each device, as the differences between reference thick, reference ultrathin and passivated ultrathin CIGS solar cells are yet to be fully understood. The analyses show a simpler AC equivalent circuit for the reference ultrathin device, which is explained by the lowered bulk recombination for thin film CIGS solar cells when compared with thick ones. The importance of shunts mitigation by the use of a passivation layer is also demonstrated, with a shunt resistance increase for the passivation device compared to both reference devices.
关键词： admittance,Cu(In,Ga)Se2,recombination,ultrathin solar cells
更新于2025-09-23 15:19:57
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[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Reciprocal relationship between photoluminescence and photocurrent in two-step photon up-conversion solar cell
摘要： Two-step photon up-conversion solar cell (TPU-SC) we have recently proposed is a single-junction solar cell containing a hetero-interface of different semiconductor materials. Although efficient two-step photon up-conversion is achieved in the TPU-SC, the detailed mechanism of intraband photoexcitation occurring at the hetero-interface is still unclear. In this study, we performed simultaneous measurements of photoluminescence and photocurrent as a function of the applying bias voltage in the TPU-SC. We experimentally demonstrate the reciprocity relationship between the radiative recombination and the photocurrent of the TPU-SC.
关键词： photovoltaic cells,gallium arsenide,quantum dots,heterojunctions,radiative recombination,photoluminescence
更新于2025-09-23 15:19:57
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Surface Engineering of Alla??Inorganic Perovskite Quantum Dots with Quasi Corea??Shell Technique for Higha??Performance Photodetectors
摘要： All-inorganic lead halide perovskites with good surface morphology show substantial prospect for optoelectronic devices. However, the anion exchange of coordinated alkylamine ligands (e.g., oleic acid and oleylamine) can detach ligands and induce more interface trap sites, subsequently to reduce device performance. In this paper, therefore, a simple solution-processed route is presented to synthesize quasi coreshell CsPbBr3formamidinium iodide (FAI = CH(NH2)2I) colloidal quantum dots (CQDs), and then it is applied as the active layer for photodetectors by finely controlling the ligands exchange. The presence of FAI = CH(NH2)2I on CsPbBr3 is confirmed by Fourier transform infrared spectroscopy. As a result, the photodetector ITO/ZnO (100 nm)/CsPbBr3 (150 nm)/Au show an enhanced specific detectivity over 1013 Jones with a responsivity of 19 A W1 under 3 mW cm2 405 nm illumination at 1.5 V. The experimental data show that the enhanced device performance is due to the improved crystallinity and less surface defects of CsPbBr3 CQDs, as the result of less alkylamine ligands is detached during its FAI passivation, thus the charge carriers’ mobility of the film is improved. Therefore, it provides a promising way for high-performance solution-processed all-inorganic CsPbBr3 based optoelectronic devices.
关键词： CsPbBr3 perovskite nanocrystals,solution-processed,surface passivation,recombination process
更新于2025-09-23 15:19:57
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[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Modeling of Injection-dependent Non-radiative Recombination via Point and Extended Defects in mc-Si
摘要： Non-radiative (NR) carrier recombination limits the efficiency of photovoltaic energy conversion. Minority carrier lifetimes in Si exhibit a variety of dependences on optical injection levels, depending on the types of defects present. To date, models of non-radiative recombination in silicon were proposed for point defects (e.g., Fe interstitials) and extended defects (e.g., dislocations). Direct measurement of local carrier concentration near recombination centers is technically difficult, therefore, computational modeling may be helpful to understand various carrier recombination pathways in materials such as mc-Si. In this paper, modeling is used to compare intensity-dependent NR recombination lifetimes in Si. The usefulness of the model goes beyond mc-Si photovoltaics.
关键词： interstitials,numerical modeling,non-radiative recombination,silicon,Dislocations
更新于2025-09-23 15:19:57