shuhui

Publication date: October 2018

Source: Nano Energy, Volume 52

Author(s): Dongliang Bai, Hui Bian, Zhiwen Jin, Haoran Wang, Lina Meng, Qian Wang, Shengzhong (Frank) Liu

Abstract

Graphical abstract

Herein, the correlation between crystallization and external factors (solubility and solvent evaporation rate) is conducted for solution-processed CsPbI₂Br film. With moderate precursor solution temperature, homogenous, pinhole-free, large crystalline grain size and thick CsPbI₂Br film was obtained, which effectively increased the light absorption, and decreased recombination loss. As a result, the optimized champion device achieved long-term stabilized PCE of 14.81%.

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.

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.

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.

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.

Polymer power: Polymer donors have shown remarkable photovoltaic performance in non‐fullerene organic solar cells (OSCs). The molecular design strategies are analyzed in terms of developing suitable polymer donors for non‐fullerene acceptors to further improve the power conversion efficiency (PCE) of non‐fullerene organic solar cells.

Abstract

Over the past few years, non‐fullerene organic solar cells have been a focus of research and their power conversion efficiencies have been improved dramatically from about 6 % to over 14 %. In addition to innovations in non‐fullerene acceptors, the ongoing development of polymer donors has contributed significantly to the rapid progress of non‐fullerene organic solar cell performance. This Minireview highlights the polymer donors that enable high‐performance non‐fullerene organic solar cells. We show the impressive photovoltaic devices results achieved by some of important classes of conjugated polymer systems in non‐fullerene organic solar cells. We discuss the molecular design strategies as far as developing matching polymer donors for non‐fullerene acceptors. We conclude with a brief summary and outlook for advances in donor polymers required for commercialization.

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.

All-inorganic perovskite nanocrystal scintillators

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

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

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.

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.