the majority of the market shares as compared to next-generation thin-film PV technologies. Nevertheless, technological challenges in improving efficiencies and decreasing the high-energy requirements connected to the fabrication of silicon PV results in a higher global warming potential. In an effort to achieve lower fabrication cost and higher efficiencies, different types of thin-film PV technologies have been developed including dyesensitized solar cells, [2,3] organic solar cells, [4,5] copper indium tin sulfur [6,7] and emerging organic-inorganic lead halide perovskite solar cells (PSCs). [8,9] The combined merits of low fabrication cost and high power conversion efficiency (PCE) are distinct features of PSCs where PCE has jumped from 3.8% [8] to 25.2% [10] in just a decade. Such a sharp increase in PCE is mainly attributed to the large absorption coefficient, [11] long carrier lifetime, [12] high trap resistance, [13] high dielectric constant, [14-16] low binding energy, [17] and tunable bandgap of 1.2−1.7 eV, [18] all combined in a single perovskite material. 1.1. Perovskite Solar Cell Device Structures A typical perovskite solar cell consists of a light-absorbing perovskite layer which is sandwiched between an electron transport layer (ETL) and a hole transport layers (HTL). To complete the device, ETL is supported on a transparent conducting oxide (TCO) front electrode, and HTL on metal-coated back contact electrode, Figure 1. There are two basic structures for the PSC: the so-called mesoporous structure, which contains a mesoporous ETL layer (i.e., mesoporous TiO 2), and the planar structure, as depicted in Figure 1a,b. Even though early reports based on mesoporous devices assumed that the perovskite infiltration through the mesoporous scaffold improved the charge carrier collection to the electrode, later investigations performed by Lee and co-workers replaced the TiO 2 with an insulating Al 2 O 3 mesoporous layer, and reported for the first time the ambipolar nature of the perovskite materials, allowing the realization of longer diffusion length. [19] This enabled the fabrication of planar devices, and gave rise to an impressive evolution of device architectures, novel materials and cell configurations either in n-i-p or p-in designs. [12,19,20] In addition, Due to a certified 25.2% high efficiency, low cost, and easy fabrication; perovskite solar cells (PSCs) are the focus of interest among the nextgeneration photovoltaic technologies. Long-term stability is one of the most challenging obstacles to bring technology from the lab to the market. In this review, applications of self-assembled monolayers (SAMs) to enhance the power conversion efficiency (PCE) and stability of PSCs is discussed. In the first part, the introduction of SAMs, and deposition techniques applied to different PSC architectures are described. In the middle section, current efforts to utilize SAMs to fine-tune the optoelectronic properties to enhance the PCE and stability are detailed. The improvements in surface morphology, energ...

Perovskite solar cells utilize metal oxide thin films as electronic transport for high performance devices. These electronic transport metal oxides are generally processed at higher temperatures. In this research we report a room temperature processed WO 3−x thin film as the electron transport layer for a high performance and low hysteresis device. The highly oxygen deficient WO 3−x film was deposited at room temperature using e-beam evaporation in high vacuum conditions. For comparison, the amount of oxygen vacancies was reduced by postannealing of the as-deposited WO 3−x films at 300 °C for 1 h in air. X-ray diffraction and Raman measurements showed no WO 3−x characteristic peak of both the as-deposited and annealed films. From X-ray photoelectron spectroscopy and electron paramagnetic resonance, the as-deposited film shows large amounts of oxygen vacancies compared to the postannealed film. The bandgap of the postannealed film increases due to reduced conductivity and thus a reduction in the device performance, mainly because of the low V oc and high current−voltage hysteresis in the forward and reverse scans. The perovskite solar cell device developed using the room temperature deposited electron transport WO 3−x layer has shown low current−voltage hysteresis. This device achieved a power conversion efficiency of 10.3% and hysteresis index of 2.1%. This work demonstrates the feasibility of the WO 3−x film as an electron transport layer for the high efficiency perovskite solar cell with reduced hysteresis fabricated at low temperature using an industrially viable e-beam evaporation method.

With the rapid development of display-related markets, transparent conductive films (TCFs) with wide viewing angles, high transmittance and low sheet resistance are in high demand. However, as a promising TCF material, metallic membranes with a submicrometer-sized periodicity pattern fabricated by currently available techniques always reveal the angle-dependent structure color which can be a major issue in the development of wide-angle viewing display-related applications. In this work, we demonstrate an Au nanomesh with disordered dual-size apertures as a novel TCF with wide viewing angles which is made via a modified nanosphere lithography technique. The as-prepared Au nanomesh film shows good optoelectronic properties (Rs = 160 Ω sq(-1), T = 80%; Rs = 8 Ω sq(-1), T = 57%) that are similar to the Au nanomesh with single size apertures, while the former exhibits excellent wide-angle viewing performance. There is no obvious change in the film when the viewing angle, the light incidence angle or the orientation of substrate vary in the range of 0-90°. In contrast, a rainbow color is observed with the film with ordered single-size apertures. Electrochromic devices based on the novel metallic film show more uniform color distribution than the devices based on metallic film with ordered single-size apertures under indoor natural light irradiation. These findings demonstrate the applicability of the Au nanomesh film with dual-size apertures in enhancing display quality of high-performance optoelectronic devices.

This work demonstrates the effect of oxygen vacancies in SnO thin films on the performance of perovskite solar cells. Various SnO films with different amounts of oxygen vacancies were deposited by sputtering at different substrate temperatures (25-300 °C). The transmittance of the films decreased from 82 to 66 % with increasing deposition temperature from 25 to 300 °C. Both X-ray photoelectron spectroscopy and electron-spin resonance spectroscopy confirmed that a higher density of oxygen vacancies was created within the SnO film at a high substrate temperature, which caused narrowing of the SnO bandgap from 4.1 (25 °C) to 3.74 eV (250 °C). Combined ultraviolet photoelectron spectroscopy and UV/Vis spectroscopy showed an excellent conduction band position alignment between the methylammonium lead iodide perovskite layer (3.90 eV) and the SnO electron transport layer deposited at 250 °C (3.92 eV). As a result, a significant enhancement of the open-circuit voltage from 0.82 to 1.0 V was achieved, resulting in an increase of the power conversion efficiency of the perovskite solar cells from 11 to 14 %. This research demonstrated a facile approach for controlling the amount of oxygen vacancies in SnO thin films to achieve a desirable energy alignment with the perovskite absorber layer for enhanced device performance.