Optimization of the energy levels at the donor-acceptor interface of organic solar cells has driven their efficiencies to above 10%. However, further improvements towards efficiencies comparable with ...inorganic solar cells remain challenging because of high recombination losses, which empirically limit the open-circuit voltage (
) to typically less than 1 V. Here we show that this empirical limit can be overcome using non-fullerene acceptors blended with the low band gap polymer PffBT4T-2DT leading to efficiencies approaching 10% (9.95%). We achieve
up to 1.12 V, which corresponds to a loss of only
/
-
= 0.5 ± 0.01 V between the optical bandgap
of the polymer and
. This high
is shown to be associated with the achievement of remarkably low non-geminate and non-radiative recombination losses in these devices. Suppression of non-radiative recombination implies high external electroluminescence quantum efficiencies which are orders of magnitude higher than those of equivalent devices employing fullerene acceptors. Using the balance between reduced recombination losses and good photocurrent generation efficiencies achieved experimentally as a baseline for simulations of the efficiency potential of organic solar cells, we estimate that efficiencies of up to 20% are achievable if band gaps and fill factors are further optimized.
Photoinduced electron transfer in a small band gap bulk heterojunction material (see figure) is studied by ultrafast spectroscopic methods. In this composite, the photo excitation initiates ultrafast ...electron transfer from the polymer to the fullerene, as in most bulk heterojunction materials. From analysis of the carrier recombination dynamics, we infer the existence of an intermediate charge transferred state from which long‐lived mobile positive and negative carriers are generated.
The quality check of PV-plants under certain operating conditions by employing infrared-imaging has acquired significance during the last years. In order to prove the reliability of these techniques ...in terms of power loss, life time, critical temperatures and failure mechanisms, fifteen PV-plants were investigated in detail. In total, about 260 dismantled modules were analyzed by power measurements as well as electroluminescence and IR-thermography. Apart from revealing the reliability of this technique, the evaluated data manifest various failure mechanisms, like cell fracture, deficient solder joints, short-circuited cells and bypassed substrings. The impact of these frequently detected defects on the resulting temperature, the IV-curve and the power output is discussed. Finally, differing defects can be diagnosed by characteristic temperature differences. In conclusion, the reliability and usefulness of infrared-mapping of PV-plants were proved with the result, that all modules having cells with increased temperature show remarkably reduced power output.
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► IR-monitoring of defect modules under operating conditions is reliable. ► IR-imaging visualizes the modules with reduced power output. ► We show frequent and typical damages of crystalline modules. ► The measured cell temperature increase correlates with specific defects.
The photoconductive properties of a novel low‐bandgap conjugated polymer, poly2,6‐(4,4‐bis‐(2‐ethylhexyl)‐4H‐cyclopenta2,1‐b;3,4‐b′dithiophene)‐alt‐4,7‐(2,1,3‐benzothiadiazole), PCPDTBT, with an ...optical energy gap of Eg ∼ 1.5 eV, have been studied. The results of photoluminescence and photoconductivity measurements indicate efficient electron transfer from PCPDTBT to PCBM (6,6‐phenyl‐C61 butyric acid methyl ester, a fullerene derivative), where PCPDTBT acts as the electron donor and PCBM as the electron acceptor. Electron‐transfer facilitates charge separation and results in prolonged carrier lifetime, as observed by fast (t > 100 ps) transient photoconductivity measurements. The photoresponsivities of PCPDTBT and PCPDTBT:PCBM are comparable to those of poly(3‐hexylthiophene), P3HT, and P3HT:PCBM, respectively. Moreover, the spectral sensitivity of PCPDTBT:PCBM extends significantly deeper into the infrared, to 900 nm, than that of P3HT. The potential of PCPDTBT as a material for high‐efficiency polymer solar cells is discussed.
The photoconductive properties of a low‐bandgap conjugated polymer, PCPDTBT (see figure), are studied. Photoresponsivities of PCPDTBT and PCPDTBT:fullerene‐derivative (PCBM) blends are comparable to those of poly(3‐hexylthiophene), P3HT, and P3HT:PCBM. The spectral sensitivity of PCPDTBT:PCBM extends significantly deeper into the IR than that of P3HT, improving solar‐light harvesting and offering potential for use in solar cells.
Abstract
Easily adjustable parameters such as area and design can affect the determination of the efficiency of donor–acceptor organic solar cells. Devices with crossing electrodes and unpatterned ...(semi)conducting organic layers can collect a non‐negligible current from regions usually not considered as part of the photovoltaic element, a fact that might lead to an overestimation of the power conversion efficiency.
For bulk‐heterojunction photovoltaic cells fabricated from conjugated polymers and a fullerene derivative, the relation between the open‐circuit voltage (Voc) and the oxidation potential for ...different conjugated polymers is studied. A linear relation between Voc and the oxidation potential is found (see figure). Based on this relation, the energy‐conversion efficiency of a bulk‐heterojunction solar cell is derived as a function of the bandgap and the energy levels of the conjugated polymer.
Aluminum doped zinc oxide (AZO) nanoparticles were redispersed in isopropyl alcohol and stabilized with different stabilizers and mixtures of stabilizers that allow for electronically functional ...particles. The size of the redispersed nanoparticles was small enough to use these suspensions to build interfacial layers in inverted polymer-fullerene solar cells. The performance of these devices was found to depend on the stabilizer used in the nanoparticle suspension. The best performance was obtained with an AZO interfacial layer built with a 3,6,9-trioxadecanoic acid and polyvinylpyrrolidone stabilized nanoparticle suspension.
•Preparation of stable aluminum doped zinc oxide nanoparticle suspensions•Different stabilizers were used to stabilize these nanoparticle suspensions.•The material was used as interfacial layers in inverted polymer solar cells.•The performance of these devices depends on the stabilizer used in the suspension.
Highly efficient, large area OPV modules achieving full area efficiencies of up to 93% of the reference small area cells are reported. The way to a no-loss up-scaling process is highlighted: ...photoelectrical conversion efficiencies of 5.3% are achieved on rigid modules and of 4.2% on flexible, roll coated ones, employing a commercially available photoactive material. Exceptionally high geometric fill factors (98.5%), achieved viastructuring by ultrashort laser pulses, with interconnection widths below 100 mu m are demonstrated.
A novel low‐bandgap conjugated polymer (PTPTB, Eg = ∼ 1.6 eV), consisting of alternating electron‐rich N‐dodecyl‐2,5‐bis(2′‐thienyl)pyrrole (TPT) and electron‐deficient 2,1,3‐benzothiadiazole (B) ...units, is introduced for thin‐film optoelectronic devices working in the near infrared (NIR). Bulk heterojunction photovoltaic cells from solid‐state composite films of PTPTB with the soluble fullerene derivative 6,6‐phenyl C61 butyric acid methyl ester (PCBM) as an active layer shows promising power conversion efficiencies up to 1 % under AM1.5 illumination. Furthermore, electroluminescent devices (light‐emitting diodes) from thin films of pristine PTPTB show near infrared emission peaking at 800 nm with a turn on voltage below 4 V. The electroluminescence can be significantly enhanced by sensitization of this material with a wide bandgap material such as the poly(p‐phenylene vinylene) derivative MDMO‐PPV.
Conjugated polymers with a bandgap < 2 eV are promising for optoelectronic devices. Implementation of the new copolymer PTPTB (see Figure) into bulk heterojunction solar cell devices and light‐emitting diodes, as well as the sensitization of electroluminescence by energy transfer from a wide bandgap polymer, are demonstrated.
•High resolution smart meter data from 20 months is analysed (3.5 M samples per unit).•A fitting algorithm finds direct and diffuse irradiation based on PV orientations.•Irradiation values allow ...simulation of PV generation and assessment of PV systems.•Underperforming PV systems and shading scenarios can be identified computationally.•Thermography is used to find defective PV modules and validate deviant PV systems.
Electrical solar power generation has a very decentral character which is posing significant challenges to monitoring and assessment due to the high number of considered systems. At the same time, with the advent of smart metering, huge amounts of data are becoming available and demand for automated approaches that are robust enough to deal with measuring gaps and noise. We propose and introduce a combined method consisting of a fitting algorithm, which works with the high temporal resolution of the smart meter data used (15 s), and an infrared thermography measurement. The results are region-specific irradiance characteristics, precise description of individual skylines for single systems derived from calculations, indication of abnormalities that should be compared with the abnormalities identified in thermal images and identification of reasons for underperformance.
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