The Influence of Photo‐Induced Space Charge and Energetic Disorder on the Indoor and Outdoor Performance of Organic Solar Cells

Beuel, Sebastian; Hartnagel, Paula; Kirchartz, Thomas

doi:10.1002/adts.202000319

Cited by 9 publications

(6 citation statements)

References 74 publications

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“…In a typical solar cell at 1 sun illumination, the series resistance R s is an important parameter that leads to efficiency losses. In organic solar cells with their relatively low mobility as compared to other photovoltaic technologies, the nonlinear resistance of the active layers is of particular concern and can lead to losses in fill factor or short-circuit current density and inhibits the fabrication of efficient solar cells with thicker active layers. , If organic solar cells are used for indoor applications, however, the current densities J flowing under normal operating conditions are substantially reduced (100 to 1000 times), which will mitigate the voltage losses Δ V = JR s over series resistances in the device. However, the reduced operating voltage at lower light intensity will naturally amplify the importance of parallel resistances as well as features of the J – V curve that resemble a parallel resistance in their effect on the current voltage curve.…”

Section: Resultsmentioning

confidence: 99%

“…Figure 11. (a) Measured saturation-current density J 0,Voc according to eq 8 plotted against the active-layer thickness on a double-logarithmic scale for devices with an active area of A = 0.06 cm 2 and for different light intensities(8,13,29, 61, and 250 mW/cm 2 ). Only data in the intensity regime was used where V oc is not affected by leakage currents through the R p and V oc ∝ ln (Φ) + const holds true.…”

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Understanding the Thickness and Light-Intensity Dependent Performance of Green-Solvent Processed Organic Solar Cells

et al. 2023

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For indoor light harvesting, the adjustable band gap of molecular semiconductors is a significant advantage relative to many inorganic photovoltaic technologies. However, several challenges have to be overcome that include processability in nonhalogenated solvents, sufficiently high thicknesses (>250 nm) and high efficiencies at illuminances typically found in indoor environments. Here, we report on the development and application of new methods to quantify and identify performance losses based on thickness- and intensity-dependent current density–voltage measurements. Furthermore, we report on the fabrication of solar cells based on the blend PBDB-T:F-M processed in the nonhalogenated solvent o-xylene. In the low-intensity regime, insufficiently high shunt resistances limit the photovoltaic performance and by analyzing current density voltage–curves for solar cells with various shunt resistances we find that ∼100 kΩ cm2 are required at 200 lux. We provide a unified description of fill factor losses introducing the concept of light-intensity-dependent apparent shunts that originate from incomplete and voltage-dependent charge collection. In experiment and simulation, we show that good fill factors are associated with a photo-shunt inversely scaling with intensity. Intensity regions with photo-shunt resistances close to the dark-shunt resistance are accompanied by severe extraction losses. To better analyze recombination, we perform a careful analysis of the light intensity and thickness dependence of the open-circuit voltage and prove that trap-assisted recombination dominates the recombination losses at low light intensities.

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Understanding the Thickness and Light-Intensity Dependent Performance of Green-Solvent Processed Organic Solar Cells

et al. 2023

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“…The pre-edge feature present for pristine DBP may originate from the irregularity in the molecular layer, 17 and the resulting energetic disorder may negatively impact device performance by inducing recombination effects or alter the electric field via local space charge effects, as extensively studied in the OSC field. 18 The results show that the work function for the interlayer almost matches the one of DBP and deviates from that of pristine 4P-NPD.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Unveiling the Energy Alignment across Ultrathin 4P-NPD Hole Extraction Interlayers in Organic Solar Cells

Ahmad

Amelot

Cruguel

et al. 2022

ACS Appl. Energy Mater.

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Molecular thin films of N,N′-di-1-naphthalenyl-N,N′-diphenyl [1,1′:4′,1″:4″,1‴-quaterphenyl]-4,4‴-diamine (4P-NPD) have been demonstrated to function as efficient exciton blocking layers in organic solar cell devices, leading to improved device performance by minimizing exciton losses and by providing hole extraction selectivity. However, the exact mechanisms have been debated, as ultrathin thicknesses of less than 1 nm are required to observe optimized device performance improvements. In this work, we conduct photoelectron spectroscopy to gain information about core levels, HOMO/LUMO levels, and work functions for the hole extraction side of an organic solar cell device consisting of the small molecule tetraphenyldibenzoperiflanthene (DBP) as an electron donor and 4P-NPD for exciton blocking/hole extraction, the latter being in contact with the hole transport layer MoO x . Using in situ deposition and characterization, we demonstrate that a negative HOMO energy offset increases with 4P-NPD thickness on the DBP donor layer, which cannot account for the improvement observed in device performance. Investigation of the 4P-NPD/MoO x interface, on the other hand, reveals shifts of the electronic levels in 4P-NPD and a band alignment that favors hole extraction while blocking for exciton/electron leakage. This appealing behavior is enhanced for ultrathin 4P-NPD films of less than 1 nm. Thus, the exciton blocking/hole extraction behavior of 4P-NPD interlayers in organic solar cell devices is confirmed and understood from the detailed energy level alignment across both interfaces, as extracted from the in situ photoelectron spectroscopy studies.

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“…[70] However, this typically only affects J sc values measured at intensities around one sun and higher while there should be no non-linearities at the low light intensities relevant for indoor applications. [71,72] Figure 2c, the quantum efficiency normalized to the maximal spectral irradiance and the resulting integrated short circuit current densities are shown for an organic solar cell with PBDB-TF-T1:BTP-4F-12 (PBDB-TF-T1:Y12) as the absorber material fabricated in our group, which was first shown in ref. [73].…”

Section: Adjusting the Output Power And Visualization Of The Methodsmentioning

confidence: 99%

“…[ 70 ] However, this typically only affects J sc values measured at intensities around one sun and higher while there should be no non‐linearities at the low light intensities relevant for indoor applications. [ 71,72 ]…”

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Comparing and Quantifying Indoor Performance of Organic Solar Cells

Lübke

Hartnagel

Angona

et al. 2021

Advanced Energy Materials

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An important application that benefits from the tuneability of band gaps in molecular semiconductors is the use of organic photovoltaics (OPV) for indoor light harvesting. The market of the internet of things (IoT) is emerging remarkably and demands to drive high amounts of off-grid low power consumption devices. [8][9][10][11][12][13] The possibility to produce solution-based, lowcost, and flexible solar foils makes OPV a good candidate to fulfill this demand. Furthermore, the absorption spectra of the active materials can be tuned chemically to match different light sources.Although efficiencies for indoor organic photovoltaics (iOPV) and other emerging indoor photovoltaics (iPV) technologies such as halide perovskites [36][37][38][39][40][41][42][43] or dye-sensitized solar cells [44][45][46][47][48][49][50] have improved substantially, it is hard to quantify progress and determine champion solar cells due to a lack of standardized comparison methods. [12,51,52] Different authors use different conditions to evaluate the performance of their devices. The set-ups differ in the illuminance value (ranging typically from 200 to 1000 lux) and the source of light, namely light emitting diodes (LED) or fluorescent lamps (FL) with varying emission spectra and color temperatures. This makes it difficult to compare devices and regularly leads to the publication of tables or figures where data is compared for different input spectra and illuminances. [43,53,54] The exact spectrum and intensity are, however, more than just a minor inconvenience for data comparison but can have a major impact on the output power at a given illuminance and the efficiency. This is due to several reasons. First, the presence of shunts [55][56][57] can have a substantial effect on the dependence of open-circuit voltage and fill factor on the light intensity under indoor conditions. [55,56,58] Second, the short-circuit current at a given illuminance strongly depends on the overlap of the materials' absorption spectra and the spectral emission power of the light source. [53,59] The exact spectrum is even more critical than for outdoor illumination, because indoor light sources have much more narrow spectra with strong emission between wavelengths of 400 and 700 nm [60,61] as compared to the air mass 1.5 global (AM1.5G) spectrum.In the worst-case scenario, an otherwise well-performing solar cell could exhibit low efficiencies if the color temperature of the light source is not suitable to the specific absorber bandgap. Standardizing indoor spectra as done for outdoor efficiency measurements is not practical given the substantial spectral differences between the used light sources. Furthermore, With increasing efficiencies of non-fullerene acceptor-based organic solar cells, thin-film technology is becoming a promising candidate for indoor light harvesting applications. However, the lack of standardized comparison methods makes it difficult to quantify progress and to compare indoor performance. Herein, a simple method to calculate the efficiency ...

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The Influence of Photo‐Induced Space Charge and Energetic Disorder on the Indoor and Outdoor Performance of Organic Solar Cells

Cited by 9 publications

References 74 publications

Understanding the Thickness and Light-Intensity Dependent Performance of Green-Solvent Processed Organic Solar Cells

Understanding the Thickness and Light-Intensity Dependent Performance of Green-Solvent Processed Organic Solar Cells

Unveiling the Energy Alignment across Ultrathin 4P-NPD Hole Extraction Interlayers in Organic Solar Cells

Comparing and Quantifying Indoor Performance of Organic Solar Cells

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