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With the unprecedented development of perovskite solar cells (PSCs), various interlayers have been investigated. Interlayers have diverse roles in shifting the energy levels, attracting and extracting charges, and passivating surface traps. These can improve the stability of PSCs, as well as their power conversion efficiency (PCE). In this study, a small molecular self-assembled monolayer (2-[carbamimidoyl(methyl)amino]acetic acid) is introduced on a SnO2 layer. The acetic acid is known as creatine, existing naturally in the human body. It is eatable and dosed by athletes for energy. Due to its structural properties, creatine can be anchored on a SnO2 layer, thus, it can strengthen the charge extraction from a perovskite layer by forming interface dipoles and reducing the work function. Also, it can passivate the defects in the perovskite layer. These properties are comprehensively investigated via various experimental techniques. With the creatine layer as a cathode interfacial layer on the SnO2 layer, the PSC employing a triple cation-based perovskite achieves the highest PCE of 20.8% and retained 90% of it after 50 days. Furthermore, 22.1% of PCE is obtained from the formamidinium-based perovskite. This report represents an interesting application of creatine as an interlayer in PSCs and suggests the possible application of other essential amino acids.

Organic–inorganic perovskites are crystalline light absorbers which are gaining great attraction from the photovoltaic community. Surprisingly, the power conversion efficiencies of these perovskite solar cells have rapidly increased by over 25% in 2019, which is comparable to silicon solar cells. Despite the many advances in efficiency, there are still many areas to be improved to increase the efficiency and stability of commercialization. For commercialization and enhancement of applicability, the development of electron transport layer (ETL) and its interface for low temperature processes and efficient charge transfer are very important. In particular, understanding the ETL and its interface is of utmost importance, and when this understanding has been made enough, excellent research results have been published that can improve the efficiency and stability of the device. Here, we review the progress of perovskite solar cells. Especially we discuss recent important development of perovskite deposition method and its engineering as well as the electron transport layer.

In addition to having proper energy levels and high hole mobility (μh) without the use of dopants, hole-transporting materials (HTMs) used in n-i-p-type perovskite solar cells (PSCs) should be processed using green solvents to enable environmentally friendly device fabrication. Although many HTMs have been assessed, due to the limited solubility of HTMs in green solvents, no green-solvent-processable HTM has been reported to date. Here, we report on a green-solvent-processable HTM, an asymmetric D–A polymer (asy-PBTBDT) that exhibits superior solubility even in the green solvent, 2-methylanisole, which is a known food additive. The new HTM is well matched with perovskites in terms of energy levels and attains a high μh (1.13 × 10–3 cm2/(V s)) even without the use of dopants. Using the HTM, we produced robust PSCs with 18.3% efficiency (91% retention after 30 days without encapsulation under 50%–75% relative humidity) without dopants; with dopants (bis(trifluoromethanesulfonyl) imide and tert-butylpyridine...

We report a simple post annealing-free (PAF) method for making uniform, large grain-sized, and highly crystalline triple cation perovskite films. In this simple process, a perovskite precursor solution was spin-coated onto a TiO 2 mesoporous substrate and as an antisolvent, diethyl ether (DEE) was subsequently dripped onto the film during spinning to produce an intermediate phase (IP) of perovskite film. This IP was immediately immersed into a DEE bath at room temperature for only 1 min in replacement of the conventional post annealing (PA) treatment. The as-prepared PAF film was characterized by X-ray powder diffraction, UV–vis absorption spectroscopy, fourier transform infrared spectroscopy, scanning electron microscopy, atomic-force microscopy, and photoluminescence spectroscopy. The overall power conversion efficiency (PCE) of the PAF devices was in the range of 18.8–19.5%, which is comparable with the reported PA devices (17.2–18.1%), mainly due to the J SC and the FF values, caused by the high absorption ability and the large crystal size with better surface smoothness in the PAF film. This efficiency is the highest reported for perovskite deposition by PAF methods. This new method enables reducing the device fabrication time at room temperature, which will reduce the cost of manufacturing efficient perovskite solar cells.

We introduce 1 step pin-hole free CH3NH3PbI3−xClx perovskite layers by using heated airflow during the nucleation stage of the perovskite. Upon employing heated air, we stimulate uniformly distributed nuclei growth, resulting in a pin-hole free planar perovskite layer. We find an optimized heated airflow of 100 °C as the optimized condition. The resulting planar device employing a conventional TiO2 electron transporting layer exhibits 17.6% average power conversion efficiency with 14.3% maximum powerpoint (MPP) efficiency. In addition, our method gives a very reproducible perovskite layer. Thus, our pin-hole free perovskite layer allows for 14.9% efficiency in a larger area device (0.71 cm2) that is generally prone to shunting paths.

Hybrid perovskites form an extremely attractive class of materials for large scale, low-cost photovoltaic applications. Fullerene-based charge extraction layers have emerged as a viable n-type charge collection layer, and in “inverted” p–i–n device architectures the solar cells are approaching efficiencies of 20%. However, the regular n–i–p devices employing fullerenes still lag behind in performance. Here, we show that partial solubility of fullerene derivatives in the aprotic solvents used for the perovskites makes it challenging to retain integral films in multilayer solution processing. To overcome this issue we introduce cross-linkable fullerene derivatives as charge collection layers in n–i–p planar junction perovskite solar cells. The cross-linked fullerene layers are insolubilized and deliver improved performance in solar cells enabled by a controllable film thickness.

Halide perovskites have prompted the evolution of the photovoltaic field and simultaneously demonstrated their great potential for application in other optoelectronic devices. A fundamental understanding of their structure-property relationship is essential to fabricate novel materials and high-performance devices. This review gives a perspective on different synthetic methodologies for the preparation of halide perovskites and highlights the effects of structural factors such as crystal structure, grain size, nanoscale dimensionality, patterned arrangement, and hierarchical structure on their optoelectronic properties. The main emphasis is given to 0D, 1D and 2D nanostructured materials including their common synthesis methods and key structural properties. Structural factors should be precisely controlled during the material preparation and device fabrication to improve the performance of targeted applications.

Recent advances in video processing and transmitting technologies have increased user interest and demand for realistic services. Among realistic services, the free-viewpoint video (FVV) streaming service has been studied. In order to provide the FVV streaming service, it is necessary to distinguish the number of videos and provide adjacent views for view switching. In this paper, we design and propose a structure that enables the client to know the relationship between views in free-viewpoint relationship description (FRD) architecture. The proposed FRD is used to implement the FVV streaming system, and the possibility of rapid new switching is verified.

Here we study perovskite solar cells based on mesoporous alumina scaffold infiltrated and capped with a perovskite absorber layer, which are devoid of a discrete n-type electron collection layer. We employ ethoxylated polyethylenimine (PEIE) to modify the interface between the perovskite absorber layer and the metallic transparent fluorine-doped SnO 2 (FTO) electrode. Surprisingly, the PEIE interlayer obviates the requirement for the conventional dense-TiO 2 (d-TiO 2 ) compact layer (or organic fullerene layer), usually required to selectively extract electrons from the perovskite film. The self-organized PEIE interlayer produced a strong induced dipole moment at the perovskite-FTO interface, with our results indicating that electrons accumulate within the perovskite film at this interface. The resultant “n-type” contact region within the perovskite absorber layer, progressing to an intrinsic (i) region within the bulk of the perovskite layer, represents an n-i homojunction and favorably enables selective electron extraction at the FTO electrode. Resulting solar cells deliver current-voltage measured power conversion efficiencies (η) of over 15.0% and a substantial stabilized efficiency (η) of 9.1%. Although our solar cell performance remains lower than the highest reported efficiencies for perovskite solar cells employing discrete charge selective extraction layers, it indicates significant potential for “homo-junction” perovskite solar cells, once the metallic-to-perovskite contact is fully controlled. Additionally, our work identifies the potential impact of modifying the interface between the perovskite absorber and the subsequent contact materials with dipolar organic compounds, which may be applicable to optimizing contact at perovskite-semiconductor heterojunctions.

An electron transporting layer (ETL) plays an important role in extracting electrons from a perovskite layer and blocking recombination between electrons in the fluorine-doped tin oxide (FTO) and holes in the perovskite layers, especially in planar perovskite solar cells. Dense TiO2 ETLs prepared by a solution-processed spin-coating method (S-TiO2) are mainly used in devices due to their ease of fabrication. Herein, we found that fatal morphological defects at the S-TiO2 interface due to a rough FTO surface, including an irregular film thickness, discontinuous areas, and poor physical contact between the S-TiO2 and the FTO layers, were inevitable and lowered the charge transport properties through the planar perovskite solar cells. The effects of the morphological defects were mitigated in this work using a TiO2 ETL produced from sputtering and anodization. This method produced a well-defined nanostructured TiO2 ETL with an excellent transmittance, single-crystalline properties, a uniform film thickness, a large effective area, and defect-free physical contact with a rough substrate that provided outstanding electron extraction and hole blocking in a planar perovskite solar cell. In planar perovskite devices, anodized TiO2 ETL (A-TiO2) increased the power conversion efficiency by 22% (from 12.5 to 15.2%), and the stabilized maximum power output efficiency increased by 44% (from 8.9 to 12.8%) compared with S-TiO2. This work highlights the importance of the ETL geometry for maximizing device performance and provides insights into achieving ideal ETL morphologies that remedy the drawbacks observed in conventional spin-coated ETLs.

Compact TiO2 is widely used as an electron transport material in planar-perovskite solar cells. However, TiO2-based planar-perovskite solar cells exhibit low efficiencies due to intrinsic problems such as the unsuitable conduction band energy and low electron extraction ability of TiO2. Herein, the planar TiO2 electron transport layer (ETL) of perovskite solar cells is modified with ionic salt CuI via a simple one-step spin-coating process. The p-type nature of the CuI islands on the TiO2 surface leads to modification of the TiO2 band alignment, resulting in barrier-free contacts and increased open-circuit voltage. It is found that the polarity of the CuI-modified TiO2 surface can pull electrons to the interface between the perovskite and the TiO2, which improves electron extraction and reduces nonradiative recombination. The CuI solution concentration is varied to control the electron extraction of the modified TiO2 ETL, and the optimized device shows a high efficiency of 19.0%. In addition, the optimized device shows negligible hysteresis, which is believed to be due to the removal of trap sites and effective electron extraction by CuI-modified TiO2. These results demonstrate the hitherto unknown effect of p-type ionic salts on electron transport material.