Optimization of charge generation in polymer blends is crucial for the fabrication of highly efficient polymer solar cells. While the impacts of the polymer chemical structure, energy alignment, and interface on charge generation have been well studied, not much is known about the impact of polymer aggregation on charge generation. Here, we studied the impact of aggregation on charge generation using transient absorption spectroscopy, neutron scattering, and atomic force microscopy. Our measurements indicate that the 1,8-diiodooctane additive can change the aggregation behavior of poly(benzodithiophene-alt-dithienyl difluorobenzotriazole (PBnDT-FTAZ) and phenyl-C61-butyric acid methyl ester (PCBM)polymer blends and impact the charge generation process. Our observations show that the charge generation can be optimized by tuning the aggregation in polymer blends, which can be beneficial for the design of highly efficient fullerene-based organic photovoltaic devices.

Organometal halides are promising materials for photovoltaic applications, offering tunable electronic levels, excellent charge transport, and simplicity of thin-film device fabrication. Two-dimensional (2D) perovskites have emerged as promising candidates over three-dimensional (3D) ones due to their interesting optical and electrical properties. However, maximizing the power conversion efficiency is a critical issue to improve the performance of these solar cells. In this work, we studied the photophysics of a two-dimensional (2D) perovskite (CH3NH3)2Pb(SCN)2I2 thin film using steady-state and time-resolved absorption and emission spectroscopy and compared it with the three-dimensional (3D) counterpart CH3NH3PbI3. We observed a higher bandgap and faster charge recombination in (CH3NH3)2Pb(SCN)2I2 compared to CH3NH3PbI3. This work provides an improved understanding of fundamental photophysical processes in perovskite structures and provides the guideline for the design, synthesis, and fabrication of solar cells.

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Conjugated polymers and small molecules have been intensively studied due to their unique electronic and optical properties. Relatively easy and inexpensive fabrication, light weight, mechanical flexibility and non-toxic processing methods open broad prospects for their applications in solar cells[1, 2]. Power conversion efficiency of about 16% [3] has been achieved in these solar cells. Significant focus of research efforts involve develop new materials or to advance processing systems to increase the power conversion efficiency (PCE)[4, 5]. Currently, there remains a question whether the processing based on the nonhalogenated solvents, called "green solvents"[6], is possible on an industrial-scale. The sustainable manufacturing of these organic electronics, because of the organic solvents used, still pose serious health problems and a harmful environmental impact. Here, we studied the morphology of the "green solvents" processed polymer blend and compared with the blend processed with "halogenated solvent" to explore the reasons for the difference in charge generation efficiency in polymer solar cells based on aliphatic side chain and oligoethylene glycol (OEG) side chain[7]. The performance of the highly efficient PPDT2FBT:PCBM [8]system with 9.2% power conversion efficiency is degraded significantly to 1.4% when PCBO12 is blended with a OEG version of a polymer namely PPDT2FBT-A[9], that has only a minor side-chain modification. We employed Atomic Force Microscopy to investigate the impact of side chain on morphology of these polymer blends.

The newly emerged family of organic-inorganic halide perovskites not only revolutionizes the field of photovoltaic research with an average PCE > 20%; but also triggers plentiful studies on optical gain, light-emitting diodes, and field-field-transistors due to the tunability of optical and electrical properties brought by the versatility of organic chemistry synthesis. Most of the works focus on achieving a higher power conversion efficiency and/or light-emitting properties through a variety of chemical synthesis, novel growth conditions, and fabrication methods [1,2]. The solution-processed three-dimensional (3D) organic-inorganic halide perovskites have shown great promise as solar cells [1] due to high charge carrier mobility, long exciton diffusion length, and low concentration of traps, but their poor stability over longer periods of time due to heat, moisture, light, etc. has stopped them from becoming widely commercialized. However, two-dimensional perovskites (2D) have emerged as a replacement for the 3D perovskites, offering superior properties such as longer lifetime, more stability, higher bandgap, and versatility of organic chemistry synthesis [3][4][5][6][7]. However, the studies on the electronic structure and properties of 2D perovskite materials are very limited. Therefore, the investigation of optoelectronic properties in relation to chemical synthesis and morphological changes is critically important. In this work, we successfully synthesized deuterated methylammonium iodide (CH 3 ND 3 I) and prepared deuterated 2D perovskite (CH 3 ND 3 ) 2 Pb(SCN) 2 I 2 thin films and studied the impact of deuteration on morphological changes. X-ray diffraction (XRD) measurements were carried out for the structural characterization and scanning electron microscopy (SEM) was used for morphological characterization.