In Situ Optical Studies on Morphology Formation in Organic Photovoltaic Blends

Abstract

layers share a similar bulk heterojunction (BHJ) structure with a well-controlled level of phase separation, consisting of a conjugated polymer as the electron donor and another polymer or small molecule as the electron acceptor. [2] It is worth noting that the micro-and nanostructures of these organic semiconductors, as well as the resulting blend morphology and the subsequent device performance, are extremely sensitive to processing conditions. Such changes in microstructure and morphology naturally occur during the film formation from solution, since the final structure of a BHJ film is determined by the interplay between solutes and solvent, including solubility and miscibility of molecules, solvent evaporation, molecular packing, phase separation, etc. [3] Over the past decades, this has led to the efforts to measure the optical properties of these materials during processing, in order to monitor, understand, and finally manipulate and optimize the film formation process.Several methods are well established to investigate the morphology formation of polymer:fullerene BHJ films. The first attempts to monitor the drying kinetics of BHJ films were done using in situ white-light or laser reflectometry, which can measure the thickness and solid content variation during drying. [4] Later on, spectroscopic ellipsometry was introduced into the in situ studies, allowing the real-time studies of the optical constant, thin-film thickness, surface roughness, optical anisotropy, and compositional change. [5] In the meantime, in situ X-ray scattering and X-ray diffraction were used, either

Energy and Charge Dual Transfer Engineering for High‐Performance Green Perovskite Light‐Emitting Diodes

“…[ 25 ] Here, the PL decay time was fitted using a bi‐exponential model given by Equation (1). [ 26 ] where I is the normalized PL intensity, t is the time elapsed after excitation, A is the bi‐exponential model constant, B 1 and t 1 are the bi‐exponential model and decay time coefficient for fast decay, respectively, and B 2 and t 2 are the same coefficients for slow decay, respectively. Subsequently, the average PL decay times ( t av ) of the samples were calculated from the fitted decay curves using Equation (2).…”

“…[25] Here, the PL decay time was fitted using a biexponential model given by Equation (1). [26] ( ) = +…”

Impact of substituents on the performance of small-molecule semiconductors in organic photovoltaic devices via regulating morphology

“…Toward this end, in situ analysis of morphology should be of critical importance; indeed, in situ light absorption, photoluminescence, and X-ray scattering analyses are becoming increasingly common in OPV research. 163–166 We also note that the use of computer-aided approaches should be widely extended to accelerate the understanding of the structure–morphology–performance relationship of OPV materials. There have been already several studies in this context, 167–173 and research efforts in this area will aid achieving PCEs nearing the theoretical limit.…”

Real-time views of morphological evolution in solution-processed organic photovoltaics

“…4, the beam can either shine perpendicular to the film, 81,89 or at a certain incident angle, 84,90 while the detector for transmittance can be placed on the other side of the film along the beamline, 81,84,89 or on the same side of the incident beam, with a reflective layer at the bottom. 75,91 Putting the incident beam and detector on different sides of the sample is a more standard way to measure absorption spectra, since it reduces the interference from the top/bottom interfaces of the sample (Fig. 4a); by tilting the incident light, the reflected signal (interference fringes) can be recorded on a separate detector, which allows the calculation of film thickness at the same time (Fig.…”

“…49,81,[95][96][97][98] Instead of steady-state PL, we recently explored the possibility of conducting in situ time-resolved photoluminescence (TRPL) in studies of BHJ formation. 91 The change of photoluminescence quantum yield (PLQY) in the drying process can be measured by TRPL, and different quenching mechanisms during solvent evaporation were well distinguished and discussed separately, which is not possible in steady-state PL.…”