Ligang Yuan

In-situ cross-linking strategy for efficient and operationally stable methylammoniun lead iodide solar cells

In-situ cross-linking strategy for efficient and operationally stable methylammoniun lead iodide solar cells, Published online: 18 September 2018; doi:10.1038/s41467-018-06204-2

Compositional and orientational control in metal halide perovskites of reduced dimensionality

Compositional and orientational control in metal halide perovskites of reduced dimensionality, Published online: 10 September 2018; doi:10.1038/s41563-018-0154-x

Significantly boosted n‐type organic thermoelectric performance of donor–acceptor (D–A) copolymers by a factor of three orders of magnitude is realized by tailoring the density of states through molecular design. This strategy improves the electrical conductivity effectively and reduces the loss of the Seebeck coefficient, leading to a very good power factor of 4.5 µW m⁻¹ K⁻² for doped D–A copolymers.

Abstract

It is demonstrated that the n‐type thermoelectric performance of donor–acceptor (D–A) copolymers can be enhanced by a factor of >1000 by tailoring the density of states (DOS). The DOS distribution is tailored by embedding sp²‐nitrogen atoms into the donor moiety of the D–A backbone. Consequently, an electrical conductivity of 1.8 S cm⁻¹ and a power factor of 4.5 µW m⁻¹ K⁻² are achieved. Interestingly, an unusual sign switching (from negative to positive) of the Seebeck coefficient of the unmodified D–A copolymer at moderately high dopant loading is observed. A direct measurement of the DOS shows that the DOS distributions become less broad upon modifying the backbone in both pristine and doped states. Additionally, doping‐induced charge transfer complexes (CTC) states, which are energetically located below the neutral band, are observed in DOS of the doped unmodified D–A copolymer. It is proposed that charge transport through these CTC states is responsible for the positive Seebeck coefficients in this n‐doped system. This is supported by numerical simulation and temperature dependence of Seebeck coefficient. The work provides a unique insight into the fundamental understanding of molecular doping and sheds light on designing efficient n‐type OTE materials from a perspective of tailoring the DOS.

The sensitive detection of X‐rays using devices based on metal halide perovskite semiconductors embodies a rapidly emerging field of research. The photophysical pathways within a single‐crystal Cs₂AgBiBr₆ detector exhibiting high sensitivity to X‐rays are detailed. By evaluating carrier‐recombination pathways at both high and low temperatures, the dramatic enhancements to performance realized upon cooling the device are elucidated.

Abstract

The sensitive detection of X‐rays embodies an important research area, being motivated by a common desire to minimize the radiation doses required for detection. Among metal halide perovskites, the double‐perovskite Cs₂AgBiBr₆ system has emerged as a promising candidate for the detection of X‐rays, capable of high X‐ray stability and sensitivity (105 μC Gy⁻¹ cm⁻²). Herein, the important photophysical pathways in single‐crystal Cs₂AgBiBr₆ are detailed at both room (RT) and liquid‐nitrogen (LN₂T) temperatures, with emphasis made toward understanding the carrier dynamics that influence X‐ray sensitivity. This study draws upon several optical probes and an RT excitation model is developed which is far from optimal, being plagued by a large trap density and fast free‐carrier recombination pathways. Substantially improved operating conditions are revealed at 77 K, with a long fundamental carrier lifetime (>1.5 µs) and a marked depopulation of parasitic recombination pathways. The temperature dependence of a single‐crystal Cs₂AgBiBr₆ X‐ray detecting device is characterized and a strong and monotonic enhancement to the X‐ray sensitivity upon cooling is demonstrated, moving from 316 μC Gy⁻¹ cm⁻² at RT to 988 μC Gy⁻¹ cm⁻² near LN₂T. It is concluded that even modest cooling—via a Peltier device—will facilitate a substantial enhancement in device performance, ultimately lowering the radiation doses required.

Graphdiyne‐ZnO composite material is prepared via a simple method and studied in detail. Zn and O atoms can coordinate bonding with graphdiyne, thus forming the CZn bond and CO bond, respectively, which improves the morphology and electrical conductivity of the interfacial layer. Polymer solar cells based on the nanocomposites obtain an enhanced power conversion efficiency of 11.2% compared with the devices with ZnO‐only (10%).

Graphdiyne‐ZnO (GDZO) composite material is prepared via a simple method and studied in detail for the first time. The transmission electron microscopy, Raman spectroscopy and X‐ray photoelectron spectroscopy (XPS) analyses confirm the formation of an adduct between GD and ZnO. Then the interaction between ZnO and GD is further investigated by first‐principles calculations. It is found that the Zn and O atom can coordinate bonding with GD, thus forming the CZn bond and CO bond, respectively. Polymer solar cells are fabricated based on the nanocomposites for the first time and an enhanced power conversion efficiency of 11.2%, compared with the devices with ZnO‐only (10%), is obtained. Simultaneously, the resultant devices show better stability, whether in glove box or in atmosphere, with humidity of 90%. The investigation of exciton generation rate, ideal current‐voltage model, and impedance spectra verify that the introduction of GDZO not only accelerates electron transfer but also reduces charge recombination occurring at the interface. The results indicate that GDZO is a promising electron transport material to enhance solar cell performance and presents a large potential for optoelectronic applications as well.

A pseudo‐3D CH₃CH₂CH₂NH₃PbI₃ perovskite film is deposited by a scalable dip‐coating technique with high surface coverage, and then conversed to a high‐quality 3D CH₃NH₃PbI₃ perovskite film via an organic‐cation displacement approach. With the MAPbI₃ film as the light absorber, planar perovskite solar cells are fabricated, affording stabilized power conversion efficiencies of 19.27% and 15.68% for 0.09 and 5.02 cm² devices, respectively.

Abstract

Methylammonium iodide (MAI) and lead iodide (PbI₂) have been extensively employed as precursors for solution‐processed MAPbI₃ perovskite solar cells (PSCs). However, the MAPbI₃ perovskite films directly deposited from the precursor solutions, usually suffer from poor surface coverage due to uncontrolled nucleation and crystal growth of the perovskite during the film formation, resulting in low photovoltaic conversion efficiency and poor reproducibility. Herein, propylammonium iodide and PbI₂ are employed as precursors for solution deposition of propylammonium lead iodide (PAPbI₃) perovskite film. It is found that the precursors have good film formability, enabling the deposition of a large‐area and homogeneous PAPbI₃ perovskite film by a scalable dip‐coating technique. The dip‐coated PAPbI₃ film is then subjected to an organic‐cation displacement reaction, resulting in MAPbI₃ film with high surface coverage and crystallinity. With the MAPbI₃ film as the light absorber, planar PSCs are fabricated, and stabilized power conversion efficiencies of 19.27% and 15.68% can be achieved for the devices with active areas of 0.09 and 5.02 cm², respectively. The technology reported here provides a robust and efficient approach to fabricate large‐area and high‐efficiency perovskite cells for practical application.

A high quality CsPbI₂Br perovskite film is prepared by a Lewis base adduct‐promoted growth process. A CsPbI₂Br perovskite solar cell (PSC) with a power conversion efficiency (PCE) of 13.54% is obtained at low temperature (120 °C). In addition, the method enables fabrication of flexible CsPbI₂Br PSC with PCE as high as 11.73%.

Abstract

All‐inorganic CsPbX₃‐based perovskites, such as CsPbI₂Br, show much better thermal and illumination stability than their organic–inorganic hybrid counterparts. However, fabrication of high‐quality CsPbI₂Br perovskite film normally requires annealing at a high temperature (>250 °C) that is not compatible with the plastic substrate. In this work, a Lewis base adduct‐promoted growth process that makes it possible to fabricate high quality CsPbI₂Br perovskite films at low temperature is promoted. The mechanism is attributed to synthesized dimethyl sulfoxide (DMSO) adducts which allow a low activation energy route to form CsPbI₂Br perovskite films during the thermal annealing treatment. A power conversion efficiency (PCE) of 13.54% is achieved. As far as it is known, this is the highest efficiency for the CsPbI₂Br solar cells fabricated at low temperature (120 °C). In addition, the method enables fabrication of flexible CsPbI₂Br PSCs with PCE as high as 11.73%. Surprisingly, the bare devices without any encapsulation maintain 70% of their original PCEs after being stored in ambient air for 700 h. This work provides an approach for preparing other high performance CsPbX₃‐based perovskite solar cells (PSCs) at low temperature, particularly for flexible ones.