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The influence of the number-average molecular weight (Mn) on the blend film morphology and photovoltaic performance of all-polymer solar cells (APSCs) fabricated with the donor polymer poly[5-(2-hexyldodecyl)-1,3-thieno[3,4-c]pyrrole-4,6-dione-alt-5,5-(2,5-bis(3-dodecylthiophen-2-yl)thiophene)] (PTPD3T) and acceptor polymer poly{[N,N'-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (P(NDI2OD-T2); N2200) is systematically investigated. The Mn effect analysis of both PTPD3T and N2200 is enabled by implementing a polymerization strategy which produces conjugated polymers with tunable Mns. Experimental and coarse-grain modeling results reveal that systematic Mn variation greatly influences both intrachain and interchain interactions and ultimately the degree of phase separation and morphology evolution. Specifically, increasing Mn for both polymers shrinks blend film domain sizes and enhances donor-acceptor polymer-polymer interfacial areas, affording increased short-circuit current densities (Jsc). However, the greater disorder and intermixed feature proliferation accompanying increasing Mn promotes charge carrier recombination, reducing cell fill factors (FF). The optimized photoactive layers exhibit well-balanced exciton dissociation and charge transport characteristics, ultimately providing solar cells with a 2-fold PCE enhancement versus devices with nonoptimal Mns. Overall, it is shown that proper and precise tuning of both donor and acceptor polymer Mns is critical for optimizing APSC performance. In contrast to reports where maximum power conversion efficiencies (PCEs) are achieved for the highest Mns, the present two-dimensional Mn optimization matrix strategy locates a PCE "sweet spot" at intermediate Mns of both donor and acceptor polymers. This study provides synthetic methodologies to predictably access conjugated polymers with desired Mn and highlights the importance of optimizing Mn for both polymer components to realize the full potential of APSC performance.

Organic-inorganic perovskite photovoltaics are an emerging solar technology.Developing materials and processing techniques that can be implemented in large-scale manufacturing is extremely important for realizing the potential of commercialization. Here we report a hot-casting process with controlled Cl − incorporation which enables high stability and high power-conversionefficiencies (PCEs) of 18.2% for small area (0.09 cm 2 ) and 15.4% for largearea (≈1 cm 2 ) single solar cells. The enhanced performance versus tri-iodide perovskites can be ascribed to longer carrier diffusion lengths, improved uniformity of the perovskite film morphology, favorable perovskite crystallite orientation, a halide concentration gradient in the perovskite film, and reduced recombination by introducing Cl − . Additionally, Cl − improves the device stability by passivating the reaction between I − and the silver electrode. Highquality thin films deployed over a large-area 5 cm × 5 cm eight-cell module have been fabricated and exhibit an active-area PCE of 12.0%. The feasibility of material and processing strategies in industrial large-scale coating techniques is then shown by demonstrating a "dip-coating" process which shows promise for large throughput production of perovskite solar modules.

Over the past fi ve years, a rapid progress in organometal-halide perovskite solar cells has greatly infl uenced emerging solar energy science and technology. In perovksite solar cells, the overlying hole transporting material (HTM) is critical for achieving high power conversion effi ciencies (PCEs) and for protecting the air-sensitive perovskite active layer. This study reports the synthesis and implementation of a new polymeric HTM series based on semiconducting 4,8-dithien-2-yl-benzo[1,2-d ;4,5-d ′]bistriazolealt -benzo[1,2-b :4,5b ′]dithiophenes (pBBTa-BDTs), yielding high PCEs and environmentally-stable perovskite cells. These intrinsic (dopant-free) HTMs achieve a stabilized PCE of 12.3% in simple planar heterojunction cells-the highest value to date for a polymeric intrinsic HTM. This high performance is attributed to effi cient hole extraction/collection (the most effi cient pBBTa-BDT is highly ordered and orients π-face-down on the perovskite surface) and balanced electron/ hole transport. The smooth, conformal polymer coatings suppress aerobic perovskite fi lm degradation, signifi cantly enhancing the solar cell 85 °C/65% RH PCE stability versus typical molecular HTMs.

In this study, a set of nitrogen-doped TiO 2 -based nanomaterials demonstrating photocatalytic activity was developed by combining the efforts of lattice doping and metal nanoparticle decoration and tested for photo-degradation of methylene blue dye by applying solar simulator irradiation. The surface potential shifts of these TiO 2 -based photocatalytic nanomaterials measured by Kelvin probe force microscope have been used to study the degree of electron generation of the photocatalysts after irradiation and were well correlated with the photocatalytic activity. The nitrogen-doped TiO 2 nanowires decorated with Pt nanoparticles can induce obvious electron accumulation and result in a large shift of surface potential. The analysis shows a clear correlation between the surface potential shift and the photodegradation activity. Furthermore, a thorough comparative photocatalytic activity study combined with X-ray photoelectron spectroscopy analysis of the materials-doped with nitrogen under various conditions-reveals that the photocatalytic efficiency of the catalysts is maintained even if the lattice doping is leached e.g., by thermal treatments after doping.