There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Despite the impressive photovoltaic performances with power conversion efficiency beyond 22%, perovskite solar cells are poorly stable under operation, failing by far the market requirements. Various technological approaches have been proposed to overcome the instability problem, which, while delivering appreciable incremental improvements, are still far from a market-proof solution. Here we show one-year stable perovskite devices by engineering an ultra-stable 2D/3D (HOOC(CH2)4NH3)2PbI4/CH3NH3PbI3 perovskite junction. The 2D/3D forms an exceptional gradually-organized multi-dimensional interface that yields up to 12.9% efficiency in a carbon-based architecture, and 14.6% in standard mesoporous solar cells. To demonstrate the up-scale potential of our technology, we fabricate 10 × 10 cm2 solar modules by a fully printable industrial-scale process, delivering 11.2% efficiency stable for >10,000 h with zero loss in performances measured under controlled standard conditions. This innovative stable and low-cost architecture will enable the timely commercialization of perovskite solar cells. Up-scaling represents a key challenge for photovoltaics based on metal halide perovskites. Using a composite of 2D and 3D perovskites in combination with a printable carbon black/graphite counter electrode; Granciniet al., report 11.2% efficient modules stable over 10,000 hours.

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One-Year stable perovskite solar cells by 2D/3D interface engineering

Hybrid perovskites are currently one of the most active fields of research owing to their enormous potential for photovoltaics. The performance of 3D hybrid organic–inorganic perovskite solar cells has increased at an incredible rate, reaching power conversion efficiencies comparable to those of many established technologies. However, the commercial application of 3D hybrid perovskites is inhibited by their poor stability. Relative to 3D hybrid perovskites, low-dimensional — that is, 2D — hybrid perovskites have demonstrated higher moisture stability, offering new approaches to stabilizing perovskite-based photovoltaic devices. Furthermore, 2D hybrid perovskites have versatile structures, enabling the fine-tuning of their optoelectronic properties through compositional engineering. In this Review, we discuss the state of the art in 2D perovskites, providing an overview of structural and materials engineering aspects and optical and photophysical properties. Moreover, we discuss recent developments along with the main limitations of 3D perovskites and assess the advantages of 2D perovskites over their 3D parent structures in terms of stability. Finally, we review recent achievements in combining 3D and 2D perovskites as an approach to simultaneously boost device efficiency and stability, paving the way for mixed-dimensional perovskite solar cells for commercial applications. Combining low-dimensional and 3D perovskites is a promising approach to achieve stable and efficient solar cells. In this Review, we discuss the structural, optical and photophysical properties of low-dimensional perovskites, compare the stability and efficiency of 2D and 3D perovskite devices, and consider 2D/3D composites as a strategy to increase the stability of perovskite solar cells.

Dimensional tailoring of hybrid perovskites for photovoltaics

Flexible and semitransparent organic solar cells (OSCs) have been regarded as the most promising photovoltaic devices for the application of OSCs in wearable energy resources and building-integrated photovoltaics. Therefore, the flexible and semitransparent OSCs have developed rapidly in recent years through the synergistic efforts in developing novel flexible bottom or top transparent electrodes, designing and synthesizing high performance photoactive layer and low temperature processed electrode buffer layer materials, and device architecture engineering. To date, the highest power conversion efficiencies have reached over 10% of the flexible OSCs and 7.7% with average visible transmittance of 37% for the semitransparent OSCs. Here, a comprehensive overview of recent research progresses and perspectives on the related materials and devices of the flexible and semitransparent OSCs is provided.

Flexible and Semitransparent Organic Solar Cells

Hybrid organic–inorganic perovskites emerged as a new generation of absorber materials for high-efficiency low-cost solar cells in 2009. Very recently, fully inorganic perovskite quantum dots also led to promising efficiencies, making them a potentially stable and efficient alternative to their hybrid cousins. Currently, the record efficiency is obtained with CsPbI3, whose crystallographical characterization is still limited. Here, we show through high-resolution in situ synchrotron XRD measurements that CsPbI3 can be undercooled below its transition temperature and temporarily maintained in its perovskite structure down to room temperature, stabilizing a metastable perovskite polytype (black γ-phase) crucial for photovoltaic applications. Our analysis of the structural phase transitions reveals a highly anisotropic evolution of the individual lattice parameters versus temperature. Structural, vibrational, and electronic properties of all the experimentally observed black phases are further inspected base...

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Anharmonicity and Disorder in the Black Phases of Cesium Lead Iodide Used for Stable Inorganic Perovskite Solar Cells

Methyl Ammonium Lead Halide Perovskite solar have shown immense potential to be a “Game Changer” in the photovoltaic industry. Major barriers to commercialization of Perovskite solar cells are poor device stability and high temperature requirement with TiO 2 electron transport layer, widely used in efficient Perovskite devices. Apart from severe moisture sensitivity and thermal degradation, Perovskite layer can be decomposed due to the TBP additive incorporation with Li-TFSI dopant in most commonly used hole transport layers like Spiro OMeTAD and P3HT. Nearly 5000 C sintering temperature requirement for Titania electron transport layer also impedes the Perovskite manufacturing in roll-to-roll process on flexible substrate which has a stringent processing condition of sub 1500 C temperature. In this work, we have introduced F4TCNQ dopant to replace TBP and Li-TFSI in P3HT HTL in a low temperature (<1500 C) solgel ZnO ETL processed Methyl Ammonium Lead Triiodide Perovskite solar cell. F4TCNQ doped P3HT HTL devices have shown over two times higher power conversion efficiency compared to pristine P3HT HTL devices. To comprehend the performance enhancement with F4TCNQ dopant in P3HT, we have examined the optical and electronic properties of both the pristine and F4TCNQ doped P3HT devices. Absorbance of Perovskite film lying underneath the undoped and the F4TCNQ doped P3HT film has been investigated to understand superior optical property of F4TCNQ incorporated film. Mott Schottky analysis has been conducted to enunciate the enhanced electronic property with F4TCNQ dopant in P3HT HTL compared to pristine P3HT.

Dian Wang

Papers

Augmentation of optoelectronic properties via P3HT doping for low temperature processed perovskite solar cell