Ligang Yuan

All-inorganic perovskite nanocrystal scintillators

All-inorganic perovskite nanocrystal scintillators, Published online: 27 August 2018; doi:10.1038/s41586-018-0451-1

2D perovskite stabilized phase-pure formamidinium perovskite solar cells

2D perovskite stabilized phase-pure formamidinium perovskite solar cells, Published online: 01 August 2018; doi:10.1038/s41467-018-05454-4

Intermolecular arrangements of PBDB‐T with ITIC and PC71BM are revealed by atomistic simulations. Owing to smaller side‐chain steric hindrance, both acceptors are prone to approach polymer A units, especially for ITIC considering better matching in size and shape. Importantly, PBDB‐T/ITIC docking occurs mainly via local π–π interaction between electron‐withdrawing end groups of ITIC and A units of the polymer, which is beneficial for efficient exciton dissociation.

Donor/acceptor (D/A) interfaces play a crucial role in photoelectric conversion for organic solar cells. However, it is impossible to experimentally probe D/A interfaces at the atomistic level to date, in particular for organic solar cells based on nonfullerene acceptors due to their anisotropic structures. In this work, we have investigated the interfacial structures of a representative D‐A copolymer donor PBDB‐T with a well‐known A‐D‐A structured nonfullerene acceptor ITIC, in comparison with a fullerene acceptor PC₇₁BM, by means of atomistic simulations. It is found that owing to different side‐chain steric hindrance between the polymer A and D units, both acceptors are more likely to approach the polymer A units, and more apparently for ITIC in consideration of the size and shape matching between the acceptors and the polymer A and D units. Importantly, docking of ITIC with polymer occurs mainly through local π–π interaction between the terminal moieties of ITIC and the A units of the polymer, and such interfacial structures are favorable for efficient exciton dissociation. Our work sheds light on the impact of side‐chain nature and location as well as acceptor structures on D/A interfaces and charge‐transfer dynamics, which will be very helpful for further improving the performance of organic photovoltaics.

Metal halide perovskites are a promising platform in light of their excellent charge transport and bandgap tunability. Especially low‐dimensional perovskites, spatially confined at the nanoscale, have further extended the degree of tunability and functionalities. Advances in perovskite materials for light emission applications and their materials properties, photophysical and electrooptic spectroscopic properties, and device performance are discussed.

Abstract

Next‐generation displays require efficient light sources that combine high brightness, color purity, stability, compatibility with flexible substrates, and transparency. Metal halide perovskites are a promising platform for these applications, especially in light of their excellent charge transport and bandgap tunability. Low‐dimensional perovskites, which possess perovskite domains spatially confined at the nanoscale, have further extended the degree of tunability and functionality of this materials platform. Herein, the advances in perovskite materials for light‐emission applications are reviewed. Connections among materials properties, photophysical and electrooptic spectroscopic properties, and device performance are established. It is discussed how incompletely solved problems in these materials can be tackled, including the need for increased stability, efficient blue emission, and efficient infrared emission. In conclusion, an outlook on the technologies that can be realized using this material platform is presented.

A series of tris(8‐hydroxyquinoline)aluminum(III) (Alq3)‐cored small molecular electrolytes, Alq3‐F1, Alq3‐F2, and Alq3‐F3, armed with ammonium functionalized fluorene units have been successfully designed and synthesized as efficient cathode interlayers (CILs) for high‐performance fullerene and non‐fullerene polymer solar cells (F‐PSCs and NF‐PSCs). The proportion of account of Alq3 segment will balance the conductivity and interfacial modification ability, whose devices exhibit the highest power conversion efficiencies (PCEs) of 10.15% in F‐PSCs and 13.75% in NF‐PSCs. Importantly, these CIL molecules have the excellent thickness‐insensitive property enabled by high electron mobility of the Alq3 core. The PCEs of the PSCs incorporating the Alq3‐containing CILs can retain about 70–80% even with a large thickness up to 50 nm.

Tris(8‐hydroxyquinoline)aluminum(III) (Alq₃)‐cored small molecular electrolytes, Alq₃‐F1, Alq₃‐F2, and Alq₃‐F3, armed with ammonium functionalized fluorene units have been successfully designed and synthesized as efficient cathode interlayers (CILs) for high‐performance fullerene and non‐fullerene polymer solar cells (F‐PSCs and NF‐PSCs). The repeating number effect of the polar group‐grafted fluorene arms is also investigated in detail on the cathode interfacial modification and the final photovoltaic performance. Increasing the amount of ammonium functionalized fluorene units will efficiently improve the interfacial dipole moment and result in lowering the work function (W _F) of the Al cathode. On the other hand, the proportion of Alq₃ segment will decrease with increasing the repeating number of the polar group‐grafted fluorene arms, which deduce the electron mobility of the target molecules. Alq₃‐F2 shows a good balance between the above two factors, whose devices exhibit the highest power conversion efficiencies (PCEs) of 10.15% in F‐PSCs and 13.75% in NF‐PSCs. Importantly, these CIL molecules have the excellent thickness‐insensitive property enabled by the high electron mobility of the Alq₃ core. The PCEs of the PSCs incorporating the Alq₃‐containing CILs can retain about 70–80% even with a large thickness up to 50 nm.

The hole extraction property of the hole transport layer based on TAPC small molecule via polymer assistance is largely improved. The average power conversion efficiency is enhanced from 17.66 ± 0.52% to 19.03 ± 0.53%, and the champion efficiency reaches 21.01%.

In this paper, inverted perovskite solar cells (PSCs) employing a novel polymer‐assisted small molecule layer as hole transport layer (HTL) are reported and the effect of mixed HTL on the device performance is investigated. It is the first time that the small molecule HTL is doped with a polymer HTL. The introduction of appropriate content of polymer into the small molecule layer will lead to a much smoother surface for the mixed HTL and largely reduced charge recombination, and most importantly, the energy level alignment is more matched with that of the perovskite via optimization of the doping content. Therefore, the hole transfer property is largely improved for the perovskite/mixed HTL composites. After the optimization of the polymer content in the mixed HTLs, an average power conversion efficiency (PCE) of 19.03 ± 0.53% is achieved, and the champion device exhibits a PCE of >21%. This work provides an effective strategy for the development of highly efficient inverted PSCs based on small molecule HTLs.

Through adjusting volume ratios between N‐dimethyl formamide and dimethyl sulfoxide, light absorbance and transmittance of perovskite films in tandem devices is up to balance. The effect of different solvents on surface structure and the photoelectric properties of FACs perovskite materials are systematically examined. The solvent engineering is further extended to a more complicated FAMACs perovskite/SHJ by delivering an optimal power conversion efficiency of 22.80%.

Owing to their rational distribution and adequate use of the solar spectrum and a high open‐circuit voltage, perovskite/silicon‐heterojunction (SHJ) tandem solar cells can exceed the theoretical limit of efficiency for crystalline silicon solar cells. To improve the performance of perovskite/SHJ tandem solar cells, the distribution of the solar spectrum and current matching between sub‐cells must be examined and optimized. This study employs mixed perovskite as the top cell, which is prepared with pure N, N‐dimethyl formamide (DMF), pure dimethyl sulfoxide (DMSO), and mixtures of these components in different volume ratios. The effect of different solvents on surface structure and the photoelectric properties of FACs perovskite materials are systematically examined. When the volume fraction of DMSO is 40%, a smooth, well passivated, high‐quality perovskite film is obtained. Most importantly, light absorbance and transmittance are balanced by applying solvent engineering to optimize perovskite films in the tandem devices. This method can be further extended to a more complicated FAMACs perovskite/SHJ by delivering a power conversion efficiency of 22.80%. This study concludes that solvent engineering is an effective and simple method for modifying the performance of monolithic perovskite/silicon tandem devices.

Metal oxides applied as transport layers in perovskite solar cells provide enhanced efficiency and improved performance in long timescales operating solar cells. Interfacial engineering of oxides can be made through organic molecules with different anchoring groups which passivate traps and reduce hysteresis. Oxides can also be employed as highly conductive electrodes when doped, or as oxide/oxide bilayers enhancing device lifetime.

Abstract

Oxides employed in halide perovskite solar cells (PSCs) have already demonstrated to deliver enhanced stability, low cost, and the ease of fabrication required for the commercialization of the technology. The most stable PSCs configuration, the carbon‐based hole transport layer‐free PSC (HTL‐free PSC), has demonstrated a stability of more than one year of continuous operation partially due to the dual presence of insulating oxide scaffolds and conductive oxides. Despite these advances, the stability of PSCs is still a concern and a strong limiting factor for their industrial implementation. The engineering of oxide interfaces functionalized with molecules (like self‐assembly monolayers) or polymers results in the passivation of defects (traps), providing numerous advantages such as the elimination of hysteresis and the enhancement of solar cell efficiency. But most important is the beneficial effect of interfacial engineering on the lifetime and stability of PSCs. In this work, the authors provide a brief insight into the recent developments reported on the surface functionalization of oxide interfaces in PSCs with emphasis on the effect of device stability. This paper also discusses the different binding modes, their effect on defect passivation, band alignment or dipole formation, and how these parameters influence device lifetime.