Perovskite solar cells have achieved the highest power conversion efficiencies on metal oxide n-type layers, including SnO 2 and TiO 2 . Despite ZnO having superior optoelectronic properties to these metal oxides, such as improved transmittance, higher conductivity, and closer conduction band alignment to methylammonium (MA)PbI 3 , ZnO is largely overlooked due to a chemical instability when in contact with metal halide perovskites, which leads to rapid decomposition of the perovskite. While surface passivation techniques have somewhat mitigated this instability, investigations as to whether all metal halide perovskites exhibit this instability with ZnO are yet to be undertaken. Experimental methods to elucidate the degradation mechanisms at ZnO-MAPbI 3 interfaces are developed. By substituting MA with formamidinium (FA) and cesium (Cs), the stability of the perovskite-ZnO interface is greatly enhanced and it is found that stability compares favorably with SnO 2 -based devices after high-intensity UV irradiation and 85 °C thermal stressing. For devices comprising FA-and Cs-based metal halide perovskite absorber layers on ZnO, a 21.1% scanned power conversion efficiency and 18% steady-state power output are achieved. This work demonstrates that ZnO appears to be as feasible an n-type charge extraction layer as SnO 2 , with many foreseeable advantages, provided that MA cations are avoided.

The authors propose a comprehensive mechanism for the improvement to optoelectronic properties observed when metal halide perovskites are exposed to light and air in ambient conditions, a process known as photo-brightening. Hydrogen peroxide is shown to be the active reagent responsible, and the authors demonstrate its use as a simple and fast post-treatment, resulting in substantial improvements to photoluminescence and photovoltaic device performance.

with outstanding optoelectronic properties. [1] In 2009, these materials were introduced in solar cells and have since established a striking increase in performance, reaching over 22% in stateof-the-art devices. [2] Here, the perovskite absorber is sandwiched between two selective charge extraction layers, that transport the charges to the electrodes. [3] Although efficient inorganic hole transporting materials (HTMs) have been reported, [4] the most well-known HTMs are the organic materials 2,2′,7,7′-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9′spirobifluorene (Spiro-OMeTAD) and polytriarylamine (PTAA). Alternatives that compete in performance have been published, [5][6][7] however, just like Spiro-OMeTAD and PTAA, most of these materials are synthesized in multistep synthetic procedures, involving (transition) metal catalyzed cross-coupling reactions, stringent reaction conditions and extensive product purification. This results in a relative high material cost, consequently leading to a significant contribution to the total device cost. [5,8,9] Additionally, the tedious synthesis hampers large State-of-the-art perovskite-based solar cells employ expensive, organic hole transporting materials (HTMs) such as Spiro-OMeTAD that, in turn, limits the commercialization of this promising technology. Herein an HTM (EDOT-Amide-TPA) is reported in which a functional amide-based backbone is introduced, which allows this material to be synthesized in a simple condensation reaction with an estimated cost of <$5 g −1 . When employed in perovskite solar cells, EDOT-Amide-TPA demonstrates stabilized power conversion efficiencies up to 20.0% and reproducibly outperforms Spiro-OMeTAD in direct comparisons. Time resolved microwave conductivity measurements indicate that the observed improvement originates from a faster hole injection rate from the perovskite to EDOT-Amide-TPA. Additionally, the devices exhibit an improved lifetime, which is assigned to the coordination of the amide bond to the Li-additive, offering a novel strategy to hamper the migration of additives. It is shown that, despite the lack of a conjugated backbone, the amide-based HTM can outperform state-of-the-art HTMs at a fraction of the cost, thereby providing a novel set of design strategies to develop new, low-cost HTMs.

Trap-related charge-carrier recombination fundamentally limits the performance of perovskite solar cells and other optoelectronic devices. While improved fabrication and passivation techniques have reduced trap densities, the properties of trap states and their impact on the charge-carrier dynamics in metal-halide perovskites are still under debate. Here, a unified model is presented of the radiative and nonradiative recombination channels in a mixed formamidinium-cesium lead iodide perovskite, including charge-carrier trapping, de-trapping and accumulation, as well as higher-order recombination mechanisms. A fast initial photoluminescence (PL) decay component observed after pulsed photogeneration is demonstrated to result from rapid localization of free charge carriers in unoccupied trap states, which may be followed by de-trapping, or nonradiative recombination with free carriers of opposite charge. Such initial decay components are shown to be highly sensitive to remnant charge carriers that accumulate in traps under pulsedlaser excitation, with partial trap occupation masking the trap density actually present in the material. Finally, such modelling reveals a change in trap density at the phase transition, and disentangles the radiative and nonradiative charge recombination channels present in FA 0.95 Cs 0.05 PbI 3, accurately predicting the experimentally recorded PL efficiencies between 50 and 295 K, and demonstrating that bimolecular recombination is a fully radiative process.

For neat Pb perovskites, two-dimensional (2D) hybrid perovskites, where n layers of inorganic material are separated by a long-chain organic cation, generally exhibit greater stability but have lower photovoltaic performance characteristics, motivating the study of 2D/3D mixeddimension systems to realize both high efficiency and stability. In this Letter, we demonstrate such optimal compromise between performance and stability using formamidinium, cesium, and t-butylammonium as A-site cations with Pb:Sn mixed-metal low-band-gap perovskites. Perovskite solar cells based on n = 4 and 5 lead−tin perovskites achieved power conversion efficiencies of up to 9.3 and 10.6%, respectively, and correspondingly retained 47 and 29% of their initial efficiency during storage in nitrogen for 2000 h. A similar stability trend for n = 4 over n = 5 was also observed for unencapsulated devices during continuous operation under a combined air atmosphere and temperature for 10 h, resulting in improved stability over the 3D lead−tin counterpart.

Recent results in the assembly of DNA into structures and arrays with nanoscale features and patterns have opened the possibility of using DNA for sub-10 nm lithographic patterning of semiconductor devices. Super-resolution microscopy is being actively developed for DNA-based imaging and is compatible with inline optical metrology techniques for high volume manufacturing. Here, we combine DNA tile assembly with state-dependent super-resolution microscopy to introduce crystal-PAINT as a novel approach for metrology of DNA arrays. Using this approach, we demonstrate optical imaging and characterization of DNA arrays revealing grain boundaries and the temperature dependence of array quality.For finite arrays, analysis of crystal-PAINT images provides further quantitative information of array properties. This metrology approach enables defect detection and classification and facilitates statistical analysis of self-assembled DNA nanostructures. IntroductionAs the costs and challenges of semiconductor device scaling increase, 1 new materials and technologies that enable precise patterning and placement of nanostructures are sought to supplement or replace current photolithography techniques. 2 For example, nanoscale patterning through directed self-assembly of block-copolymer (BCP) structures has been acknowledged as a viable and inexpensive lithographic mask via the International Technology Roadmap for Semiconductor manufacturing. 3,4 While progress has been made in the precise control of BCP self-assembly, defect densities and directed self-assembly of complex patterns remain challenges for manufacturing. 5 As an alternative technology, the potential for programmable, long-range order through self-assembly makes DNA an attractive material for bottom-up fabrication of nanoscale patterns, 6 as well as for templated-assembly of electronic and photonic devices with nanometer precision. 7-10Within the last two decades, DNA-based techniques such as origami, 6 tiles, 9 and bricks 11 have demonstrated precise control over the size, shape, arrangement, and assembly of DNA nanostructures and nanocomponents. While much work is still needed to approach commercial viability, lithographically confined DNA origami and large crystalline arrays of DNA origami show potential as self-assembled lithographic masks 12 and templates for precise nanoparticle assemblies. 13-18As a result of these advances, the Semiconductor Research Corporation recently listed DNAcontrolled sub-10 nm manufacturing as a technical area for its future roadmap. 19Beyond the ability to pattern at the nanoscale, metrology of patterned structures is a crucial capability in semiconductor device manufacturing that poses increasing challenges (e.g., cost, throughput, accuracy) as the device dimensions decrease. 20,21 For example, locating dislocations within a nanoscale BCP pattern requires tedious inspection of highresolution scanning electron micrographs. Likewise, common high-resolution imaging techniques used for characterization of DNA nanostructures, such as...

While perovskite solar cells (PSCs) have been developed with different device architectures, mesoporous devices have provided the highest power conversion efficiencies. In this work, the working mechanism of both positive-intrinsic-negative (p-i-n) and negative-intrinsic-positive (n-i-p) meso-superstructured (MSSC) PSCs, which include a thin interlayer of porous alumina at the bottom electrode, is explored. Interestingly, for both p-i-n and n-i-p architecture, the mesoporous configuration was more efficient than its planar counterpart. For MSSC SnO 2 -based n-i-p devices, that result was primarily due to an increase in V oc and J sc , resulting from improved band alignment and filling of the electron trap states (n-doping at the SnO 2 /perovskite interface), which led to devices with 21.0% efficiency and 20.3% stabilized power output (SPO). Although MSSC NiO x -based p-i-n meso-superstructured devices were less efficient due to lower V oc , a slightly higher J sc and fill factor improvement was achieved by the Al 2 O 3 mesoporous layer, resulting in devices with 16.9% efficiency. Importantly, the electronic nature of the perovskite is dependent upon its physical confinement within a mesoporous scaffold. Therefore, either p-or n-type semiconductor/perovskite interfaces can be engineered by selectively modifying the semiconductor behavior with the introduction of an insulating mesoporous scaffold interlayer.

A crosslinkable acrylate random copolymer with both bis(triarylamine) and photocrosslinkable cinnamate side chains is compared to the widely used poly(4-butyl-triphenylamine-4′,4′′-diyl) as a hole-transport material in perovskite solar cells.