Comparing and Quantifying Indoor Performance of Organic Solar Cells

Abstract

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 ...

ITO‐Free Indoor OPV Modules from Nonhalogenated Solvents

“…[ 20 ] However, many different lamp types are used and, without properly defined mismatching of the spectra, direct comparisons of absolute values of different groups are rather meaningless. Lübke et al [ 21 ] have made a proposition on how to compare the different values from different groups, given the spectra, EQE and J SC values are presented. The biggest challenge here will be to measure an absolute EQE.…”

“…[20] However, many different lamp types are used and, without properly defined mismatching of the spectra, direct comparisons of absolute values of different groups are rather meaningless. Lübke et al [21] have made a proposition on how to compare the different values from different groups, 2. Current density-voltage characteristics for inverted ITO-based (blue) and ITO-free devices with (black) reduced work function and (red) conductive PEDOT:PSS (FHC formulation from Heraeus) with an active area of 0.1 cm 2 , comprising TPD-3F:IT-4F as absorber material.…”

Over 30% Efficient Indoor Organic Photovoltaics Enabled by Morphological Modification Using Two Compatible Non‐Fullerene Acceptors

“…For clarity, Figure S13 and Table S3 (Supporting Information) compare the indoor performance between our ternary OPV and the state‐of‐the‐art binary OPVs comprising IT‐4F acceptors reported previously in the literature. As previously reported, [ 43 ] a comparison of indoor performance measured under different irradiation conditions can be performed using SQ limit data for different lamp conditions (such as lux value, lamp type, and color temperature). The unprecedented high PCE in our ternary OPVs reflects that the ternary strategy involving two compatible non‐fullerene acceptors can be a platform to boost the performance of indoor OPVs and overcome efficiency limitations in currently existing indoor OPV materials and devices.…”

“…Figure 3e,f shows the SQ limit photovoltaic parameters as a function of device onset energy (called as energy bandgap), which were obtained by applying the SQ model to the emission spectrum of 500 lux 3000 K LED. [43,44] Figure S12 (Supporting Information) shows EQE spectra of the two devices as a function of quantitative photon energy used to obtain their onset energy values. The addition of ITIC-Th in the PM6:IT-4F blend was particularly effective in increasing V OC and FF values, which was consistent with the charge recombination behavior in the devices.…”

Tunable Photovoltaics: Adapting Solar Cell Technologies to Versatile Applications

“…[481] Obviously, these conditions imply different optimal design of PV devices compared to conventional solar cells under sunlight. [39,[482][483][484][485] A wide range of organic and inorganic photoabsorbent materials have been extensively studied for IPV devices in literature. [40,481,[486][487][488][489][490][491][492][493][494][495] However, the selected photosensitive materials for IPV technologies must satisfy a matching absorption with the emission spectrum of the indoor light source, to avoid the detrimental influence of trap-assisted recombination in the low carrier density regime, as well as minimal voltage losses with low sensitivity to weak illuminance.…”