Passivation and interlayer engineering are important approaches to increase the efficiency and stability of perovskite solar cells. Thin insulating dielectric films at the interface between the perovskite and the charge carrier transport layers have been suggested to passivate surface defects. Here, we analyze the effect of depositing poly­(methyl methacrylate) (PMMA) from a very low-concentration solution. Spatial- and time-resolved photoluminescence and atomic force microscopy analyses of samples with diverse morphologies demonstrate the preferential deposition of PMMA in topographic depressions of the perovskite layer, such as grain and domain boundaries. This treatment results in an increase in the fill factor of more than 4% and an absolute efficiency boost exceeding 1%, with a maximum efficiency of 20.4%. Based on these results, we propose a physical isolation mechanism rather than a chemical passivation of perovskite defects, which explains not only the data of this study but also most results found in earlier works.

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Wide band-gap perovskite solar cells have the potential for a relatively high output voltage and resilience in a degradation-inducing environment. Investigating the reasons why high voltages with adequate output power have not been realized yet is an underexplored part in perovskite research although it is of paramount interest for multijunction solar cells. One reason is interfacial carrier recombination that leads to reduced carrier lifetimes and voltage loss. To further improve the Voc of methylammonium lead tri-bromide (MAPbBr3), that has a band-gap of 2.3 eV, interface passivation technique is an important strategy. Here we demonstrate two ultrathin passivation layers consisting of PCBM and PMMA, that can effectively passivate defects at the TiO2/perovskite and perovskite/spiro-OMeTAD interfaces, respectively. In addition, perovskite crystallization was investigated with the established anti-solvent method and the novel flash infrared annealing (FIRA) with and without passivation layers. These modifications significantly suppress interfacial recombination providing a pathway for improved VOC’s from 1.27 to 1.41 V using anti solvent and from 1.12 to 1.36 V using FIRA. Furthermore, we obtained more stable devices through passivation after 140 h where the device retained 70% of the initial performance value.

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A metal-free organic sensitizer, suitable for the application in dye-sensitized solar cells (DSSCs), has been designed, synthesized and characterized both experimentally and theoretically. The structure of the novel donor-acceptor-π-bridge-acceptor (D-A-π-A) dye incorporates a triphenylamine (TPA) segment and 4-(benzo[c][1,2,5]thiadiazol-4-ylethynyl)benzoic acid (BTEBA). The triphenylamine unit is widely used as an electron donor for photosensitizers, owing to its nonplanar molecular configuration and excellent electron-donating capability, whereas 4-(benzo[c][1,2,5]thiadiazol-4-ylethynyl)benzoic acid is used as an electron acceptor unit. The influences of I /I , [Co(bpy) ] and [Cu(tmby) ] (tmby=4,4',6,6'-tetramethyl-2,2'-bipyridine) as redox electrolytes on the DSSC device performance were also investigated. The maximal monochromatic incident photon-to-current conversion efficiency (IPCE) reached 81 % and the solar light to electrical energy conversion efficiency of devices with [Cu(tmby) ] reached 7.15 %. The devices with [Co(bpy) ] and I /I electrolytes gave efficiencies of 5.22 % and 6.14 %, respectively. The lowest device performance with a [Co(bpy) ] -based electrolyte is attributed to increased charge recombination.

The preparation of high-quality perovskite thin films with a low concentration of defects has recently been achieved through cation engineering using, for example, Cs halide salts. However, many Cs salts cannot be adopted readily due to their frequent insolubility in typical N,N-dimethylformamide (DMF) or dimethyl sulfoxide (DMSO) solvent systems. Herein, we report the application of green, rapid, and solvent-free mechanosynthetic ball-milling for the incorporation of the otherwise insoluble CsBr to realize wide band-gap perovskite solar cells (PSCs). We mechanically synthesize triple-cation (cesium (Cs)/formamidinium (FA)/methylammonium (MA)) wide band-gap perovskites, resulting in subsequent powders that were soluble in mixed DMF/DMSO (4:1, V/V) solvents. Otherwise, the preparation of triple cations for wide band-gap perovskites through conventional solution processing could not be realized. The use of mechanosynthesis perovskites for thin-film formation allows for the growth of relatively large crystalline grains with grains diameter in the range of 500–700 nm. The champion device achieved a maximum PCE of 7.3% (7.03% stabilized), with J SC of 7.08 mA cm–2, V OC of 1.48 V, and a fill factor (FF) of 70%. This performance and voltage are among the highest reported for wide band-gap PSC devices incorporating triple-cation Cs x (FA y MA(1–y))(1–x)PbBr3 perovskites. These results show that the use of a mechanosynthetic strategy to add insoluble dopants to wide band-gap perovskites provides a promising strategy for the formation of high-quality films. Furthermore, mechanoperovskite showed higher phase purity, V OC, and efficiency as compared to the conventional solution-processed devices.

Scheme1.Synthetic route to L156 and L224. [Pd 2 (dba) 3 ] = tris(dibenzylideneacetone)dipalladium,P ( o-tol) 3 = tri(o-tolyl)phosphine.

Considering different solar dyes configuration, four novel metal‐free organic dyes based on phenoxazine as electron donor, thiophene and cyanovinylene linkers as the π‐conjugation bridge and cyanoacrylic acid as electron acceptor were designed to optimize open circuit voltage and short circuit current parameters and theoretically inspected. Density functional theory and time‐dependent density functional theory calculations were used to study frontier molecular orbital energy states of the dyes and their optical absorption spectra. The results indicated that D2‐4 dyes can be suitable candidates as sensitizers for application in dye sensitized solar cells and among these three dyes, D3 showed a broader and more bathochromically shifted absorption band compared to the others. The dye also showed the highest molar extinction coefficient. This work suggests optimizing the configuration of metal‐free organic dyes based on simple D‐ π‐A configuration containing alkyl chain as substitution, starburst conformation, and symmetric double D‐ π‐A chains would produce good photovoltaic properties.