On Optoelectronic Processes in Organic Solar Cells: From Opaque to Transparent

Abstract

Organic (semi)transparent photovoltaics (ST‐OPVs) promise integrated, sustainable, low‐cost energy harvesting solutions. However, current efficiency limitations have to be overcome to make ST‐OPV a competitive technology. In this simulation‐based work, the effect of the selective transparency on the photoelectronic processes in ST‐OPVs is studied and changes in the generation–recombination dynamics and the extraction efficiency are demonstrated that are causally linked to the increased transparency. The study of five model systems with transparent indium tin oxide (ITO) back electrodes and systematically varied extinction coefficients and an opaque cell with Ag back contact allows to quantify these changes in the photoelectronic processes and to address the role of the series and the shunt resistors while keeping all other parameters of the modeled devices identical. The findings demonstrate the increased importance of the active layer quality in ST‐OPVs and indicate that ST‐OPVs benefit from a wider choice of transparent electrode materials.

Effect of Palladium‐Tetrakis(Triphenylphosphine) Catalyst Traces on Charge Recombination and Extraction in Non‐Fullerene‐based Organic Solar Cells

“…The optical properties of the active layer, in conjunction with those of all other device layers as well as the device architecture, determine the amount of light absorbed and the interference pattern within the device and the active layer. [ 80,85,86 ] A change in the optical properties will result in a change of the generation rate G of charge carriers that are photo‐generated in the active layer, and with that, the theoretical maximum of the J sc changes. We illuminated the devices with a solar simulator and measured the current voltage‐characteristics to obtain the saturated photocurrent J ph,sat at large reverse bias.…”

Optical Expediency of Back Electrode Materials for Organic Near-Infrared Photodiodes

“…The optical field distribution of the device stack is determined by the interplay of the layer thicknesses, the optical constants of all layers, and the incident illumination. , Therefore, it is crucial to know the optical constants, n and k , of all layers in the first step. The refractive indices ( n ) of the P3HT:PC 60 BM and PCE10:COTIC-4F blends used in this work are shown in Figure , as published in previous work and the literature. , The refractive index is defined as the ratio of the phase velocity of light in vacuum and the phase velocity of light in the material; the difference between the refractive indices of adjunct layers in the device defines the reflection of the light that passes through the device stack at each interface. , In both blends, n is in a range that is typical for organic semiconducting materials, ranging from about 1.2 to 2.6. ,,, The extinction coefficient k of both blends is shown in Figure j; k is directly proportional to the absorption coefficient α via the relationship , with λ being the wavelength, and describes the exponential decay of the light as it passes through the material. , It is evident that the fullerene-based system absorbs in the narrow range between 300 and 620 nm, with the peak absorption around 500 nm, whereas the ultra-narrow-band gap PCE10:COTIC-4F blend reaches its maximum at 961 nm and extends into the near-IR region to wavelengths of 1100 nm. The optical constants of the electrode materials Au, Ag, and Al show a characteristic dispersion for each of the metals (Figure k,l), which differs significantly from that of graphite. ,, The refractive indices of the metals reveal a strong wavelength dependence and are of larger values, as expected for the highly reflective metals.…”

“…Organic Semiconductors have accumulated interest in a wide range of electronic applications in the past years. Thanks to their tunability on the molecular level, mechanical flexibility, solution processability, and low-cost fabrication, they possess great potential for new applications. − For example, the molecular tunability allows for the realization of building integrated transparent organic photovoltaics (OPVs) and the design of biocompatible, flexible organic photodetectors (OPDs) for health monitoring. ,,− Such applications have only become possible since the development of non-fullerene acceptor (NFA) molecules has introduced targeted molecular design strategies that allow control over the band gap, which has led to the development of narrow- and ultra-narrow-band gap organic semiconductors. ,− As a result, the absorption range has been extended or shifted toward the near-infrared (near-IR) region compared to the earlier generation of wide-band gap organic semiconductors that were based on fullerene acceptors, such as [6,6]-phenyl C 61 butyric acid methyl ester (PC 60 BM), [6,6]-phenyl C 71 butyric acid methyl ester (PC 70 BM), and their derivatives. − Many efforts have been channeled toward understanding and improving the NFA-based active layers of OPVs and photodiodes, ,− resulting in OPVs with remarkable PCEs of up to 18% and OPDs with detectivities of over 10 12 Jones in the near-IR (1010 nm) region. ,,, …”

Visible to Near‐Infrared Photodiodes with Advanced Radiation Resistance

“…With the device architecture, layer thicknesses, and all optical constants given, we simulated position and wavelength‐dependent G ( x,λ ) under a constant spectral intensity illumination with the available, well‐established Transfer Matrix method software (see Figure ). [ 72,73,75,76 ] The constant spectral intensity illumination is chosen to compare the generation rate originating from different wavelengths. The maximum photogeneration rate (300–700 nm) is located in the front part of the active layer next to the TiN/CdTe interface.…”