Ligang Yuan

Carboxyl‐substituted perylene (PTCA) has been successfully applied as the electron‐transport layer in perovskite solar cells. By the carboxyl groups, PTCA can effectively connect the perovskite layer and FTO, thus reducing the interface barriers induced by weak contact, resulting in a high PCE of 16.09%. In addition, the PTCA‐based devices exhibit remarkable stability under illumination in ambient conditions without encapsulation.

Carboxyl‐substituted perylene (PTCA) has been successfully applied as the electron‐transport layer in perovskite solar cells. The large rigid π–π conjugated plane structure in PTCA endows it excellent electronic transmission performance. By the carboxyl groups, PTCA can effectively connect the perovskite layer and FTO, thus reducing the interface barriers induced by weak contact, resulting in a high PCE of 16.09%. In addition, the PTCA‐based devices exhibit remarkable stability under illumination in ambient conditions without encapsulation.

Transformation from crystalline precursor to perovskite in PbCl₂-derived MAPbI₃

Transformation from crystalline precursor to perovskite in PbCl₂-derived MAPbI₃, Published online: 27 August 2018; doi:10.1038/s41467-018-05937-4

A type of macroscopic planar metasurface absorber with light near‐perfectly and exclusively absorbed by the ultrathin semiconductor film is theoretically and experimentally demonstrated via a general strategy. Guided by this strategy, colored perovskite solar cells are further designed to meet all the desired characteristics including high power conversion efficiency, high‐purity, tunability, and angle‐insensitive colors.

Abstract

The achievement of perfect light absorption in ultrathin semiconductor materials is not only a long‐standing goal, but also a critical challenge for solar energy applications, and thus requires a redesigned strategy. Here, a general strategy is demonstrated both theoretically and experimentally to create a planar metasurface absorber comprising a 1D ultrathin planar semiconductor film (replacing the 2D array of subwavelength elements in classical metasurfaces), a transparent spacer, and a metallic back reflector. Guided by derived formulisms, a new type of macroscopic planar metasurface absorber is experimentally demonstrated with light near‐perfectly and exclusively absorbed by the ultrathin semiconductor film. To demonstrate the power and simplicity of this strategy, a prototype of a planar metasurface solar cell is experimentally demonstrated. Furthermore, the device model predicts that a colored planar metasurface perovskite solar cell can maintain 75% of the efficiency of its black counterpart despite the use of a perovskite film that is one order of magnitude thinner. The displayed cell colors have high purities comparable to those of state‐of‐the‐art color filters, and are insensitive to viewing angles up to 60°. The general theoretical framework in conjunction with experimental demonstrations lays the foundation for designing miniaturized, planar, and multifunctional solar cells and optoelectronic devices.

Ohmic transition at contacts key to maximizing fill factor and performance of organic solar cells

Ohmic transition at contacts key to maximizing fill factor and performance of organic solar cells, Published online: 15 August 2018; doi:10.1038/s41467-018-05200-w

Understanding how excess lead iodide precursor improves halide perovskite solar cell performance

Understanding how excess lead iodide precursor improves halide perovskite solar cell performance, Published online: 17 August 2018; doi:10.1038/s41467-018-05583-w

Unraveling exciton–phonon coupling in individual FAPbI₃ nanocrystals emitting near-infrared single photons

Unraveling exciton–phonon coupling in individual FAPbI₃ nanocrystals emitting near-infrared single photons, Published online: 20 August 2018; doi:10.1038/s41467-018-05876-0

Electron‐selective contacts (ESLs) with tailored properties show improved device performance in both mesoporous and planar perovskite solar cells. The recent development of metal oxide and organic molecules as ESLs is summarized. Understanding the role of various ESLs in different device architectures is a key to achieve high efficiency and long‐term stability.

Abstract

Perovskite solar cells (PSCs) have attracted much attention as efficiencies go beyond 22%. To achieve these impressive numbers, the PSC scientific community is working to improve both the perovskite optoelectronic properties, and, importantly, the interfacial properties of the adjacent electron selective contacts (ESLs). Improvements in both fronts have happened concurrently and are responsible for these rapid efficiency gains. Here, the authors review the recent advances in understanding the role of ESLs on performance improvements. ESLs can be prepared from either organic and inorganic semiconductors, or a combination of both, and their key characteristics are summarized in detail. Current state‐of‐the‐art PSCs employ fully inorganic ESLs made of a thin mesoporous TiO₂ or a planar SnO₂, with reported certified efficiencies of 22.7 and 20.9%, respectively. While TiO₂ shows excellent performance in the short term, it has also been shown to induce solar cell degradation due to its UV absorption properties. Understanding ESLs has been instrumental in the rapid development of PSCs; however, some challenges remain in terms of understanding the role of different ESLs on the long‐term stability of the devices.

Atmospheric pressure spatial atomic layer technique (s‐ALD) has been adopted to introduce a ZnO buffer layer in the p‐i‐n planar perovskite solar cell architecture. The s‐ALD layer successfully prevents damages during ITO sputtering deposition, enabling the fabrication of efficient and stable semitransparent bifacial perovskite solar cells.

The replacement of the conventional top metal contact with a semi‐transparent conducting electrode such as sputtered indium‐tin oxide (ITO) is strictly required to adopt the perovskite solar cell (PSC) in hybrid tandem photovoltaic applications. In order to prevent sputtering damages on the perovskite absorber and the organic materials adopted in p‐i‐n planar architecture, an atmospheric pressure spatial atomic layer deposited (s‐ALD) ZnO buffer layer has been included. The use of a 45 nm thick s‐ALD layer enables the fabrication of a PSC with a power conversion efficiency (PCE) of 14.7%, with a similar PCE when illuminated from the ITO/s‐ALD ZnO side. When adopted in a four terminal configuration with a c‐Si solar cell (PCE of 18.6%), a 2.5% absolute PCE gain is observed with respect to the stand alone c‐Si. Finally, the semi‐transparent PSC shows an excellent shelf life, and only −4% degradation on the tracked maximum power point when encapsulated and aged at 65 °C in an inert atmosphere after 1500 h.

A simple Ti cathode interlayer is incorporated in planar structure perovskite solar cells. The Ti interlayer is able to improve the uniformity of top metal electrode layer. In addition, a Ti‐N bonding layer is formed at the Ti/perovskite interface, which passivates the traps at perovskite surface, resulting in a decent power conversion efficiency of 18.1%.

Electron and hole transport layers play a critical role in high performance metal halide perovskite solar cells. Many organic and inorganic electron/hole transport layers are developed and studied in the last few years. In this work, the authors innovatively use a ultra‐thin layer of titanium (Ti) as a cathode interlayer between metal electrode and perovskite film, without using any organic or inorganic electron transport layers, in planar heterojunction perovskite solar cells. X‐ray photoelectron spectroscopy and soft X‐ray absorption near edge structure results prove that Ti film forms a bonding layer with nitrogen (N) atoms in metylammonium anions at perovskite/Ti interface, which passivates surface defects and suppresses surface decomposition of perovskite film. The champian solar cell based on methylammonium lead iodide (CH₃NH₃PbI₃) shows a short circuit current density of 22.5 mA cm⁻², a open circuit voltage of 1.03 V and a fill factor of 78.2%, yielding a power conversion efficiency of 18.1%. Notably, Ti has low diffusivity and serves as a compact blocking layer that prevents the diffusion of metal atoms into the perovskite layer, resulting in improved device stability. Our work shows that Ti is a promising low‐cost material to replace organic and inorganic electron transporting layers for efficient perovskite solar cells.

We developed highly efficient ternary all‐polymer solar cells by incorporating a narrow‐bandgap electron‐donating polymer (PNTB) into blended films of the wide‐bandgap electron‐donating copolymer PBTA‐BO and the electron‐accepting copolymer N2200. The device based on the ternary blend film exhibites a substantially higher power conversion efficiency than its binary counterparts, which is attributable to a complementary absorption profile, efficient energy transfer, enhanced charge mobility, and improved morphology.

Ternary all‐polymer solar cells (all‐PSCs) attract considerable research attention owing to the simplicity of the single‐junction device architecture and the broad absorption range of the light‐harvesting layer. However, the difficulty in controlling the morphology of ternary blended films makes it challenging to develop high‐performance ternary all‐PSCs. Herein, we report on the development of efficient ternary blended all‐PSCs by incorporating the narrow‐bandgap electron‐donating polymer PNTB, which contains a naphtho[1,2‐c:5,6‐c′]bis([1,2,5]thiadiazole) moiety, into blend films comprising the wide‐bandgap electron‐donating copolymer PBTA‐BO and the electron‐accepting copolymer N2200. The resulting ternary blended devices reached an impressively high power conversion efficiency of 10.09%, which obviously outperforms those obtained from binary blended counterparts. The improved photovoltaic performance is attributable to the combined effects of the extended absorption profile, a favorable film morphology, and more efficient charge transfer. Of particular interest is that these ternary blend films are processed using a non‐halogenated solvent, 2‐methyltetrahydrofuran, which is promising for practical applications. These findings lend credence to the ternary approach as a facile and promising strategy for achieving high‐performance all‐PSCs.