The instability of top interface induced by interfacial defects and residual tensile strain hinders the realization of long-term stable n-i-p regular perovskite solar cells (PSCs). Herein, one molecular locking strategy is reported to stabilize top interface by adopting polydentate ligand green biomaterial 2-deoxy-2,2-difluoro-d-erythro-pentafuranous-1-ulose-3,5-dibenzoate (DDPUD) to manipulate the surface and grain boundaries of perovskite films. Both experimental and theoretical evidence collectively uncover that the uncoordinated Pb2+ ions, halide vacancy, and/or IâPb antisite defects can be effectively healed and locked by firm chemical anchoring on the surface of perovskite films. The ingenious polydentate ligand chelating is translated into reduced interfacial defects, increased carrier lifetimes, released interfacial stress, and enhanced moisture resistance, which should be liable for strengthened top interface stability and inhibited interfacial nonradiative recombination. The universality of the molecular locking strategy is certified by employing different perovskite compositions. The DDPUD modification achieves an enhanced power conversion efficiency (PCE) of 23.17-24.47%, which is one of the highest PCEs ever reported for the devices prepared in ambient air. The unsealed DDPUD-modified devices maintain 98.18% and 88.10% of their initial PCEs after more than 3000 h under a relative humidity of 10-20% and after 1728 h at 65 °C, respectively.
Two-dimensional (2D) auxetic materials have recently attracted considerable research interest due to their excellent mechanical properties and diverse applications, surpassing those of three-dimensional (3D) materials. This study focuses on the theoretical prediction of mechanical properties and auxeticity in 2D M2X (M = Cu, Ag, Au; X = S, Se, Te) monolayers using first-principles calculations. Our results indicate that the dynamically stable monolayers include low-energy α-Cu2S, α-Cu2Se, α-Cu2Te, ß-Ag2S, ß-Ag2Se, α-Ag2Te, ß-Au2S, ß-Au2Se and α-Au2Te. These M2X monolayers possess positive Poisson's ratios (PR) ranging from 0.09 to 0.52, as well as Young's moduli ranging from 19.92 to 35.42 N m-1 in x and y directions. Specially, α-Cu2S exhibits the lowest negative PR in θ = 45° × n (n = 1, 2, 3, 4) directions. The Poisson's function (PF) can be adjusted by increasing tensile strains. The ß-phase monolayers exhibit positive PF with a linear change. Interestingly, the transition from positive to negative PF occurs in the α-Cu2S and α-Ag2Te monolayers at strains greater than +3% and +4%, respectively, while the α-Cu2Se, α-Cu2Te and α-Au2Te monolayers maintain positive PF within the range of 0% to +6% strains. Furthermore, taking α-Cu2S (α-Cu2Te) as an example, the mechanism underlying negative (positive) PF is demonstrated to involve increased (decreased) bond angles, decreased thickness, and weakened (enhanced) d(M)-p(X) orbital coupling. The findings of this study not only enrich the family of 2D group-11 chalcogenides but also provide insights into their mechanical properties, thereby expanding their potential applications in mechanics.
Graphene-based (G-based) heterostructures have recently attracted considerable research interest in the field of two-dimensional nanodevices owing to their superior properties compared with those of separate monolayers. In this study, the electronic properties and Schottky barrier heights (SBHs) of G/XAu4Y (X, Y = Se, Te) heterostructures were systematically analyzed through first-principles calculations. G/SeAu4Se, G/SeAu4Te, and G/TeAu4Se are n-type Schottky contacts with Φn = 0.40, 0.38, and 0.55 eV respectively, whereas G/TeAu4Te is a p-type Schottky contact with Φp = 0.39 eV. In G-based heterostructures consisting of SeAu4Te that has a 0.22-Debye intrinsic dipole moment, the intrinsic dipole moments in different directions enhance or weaken the interfacial dipole moments corresponding to the charge transfer at the interface, resulting in different Φn values of G/SeAu4Te and G/TeAu4Se. Furthermore, vertical strain and external electric field, which influence charge transfer, are applied to G/XAu4Y heterostructures to modulate their SBHs. Taking G/TeAu4Te as an example, the p-type contact transforms into an almost ohmic contact with decreasing vertical strain or positive external electric field. The findings of this study can provide insights into the fundamental properties of G/XAu4Y for further research.
Thermoelectric (TE) technology, which can convert scrap heat into electricity, has attracted considerable attention. However, broader applications of TE are hindered by lacking high-performance thermoelectric materials, which can be effectively progressed by regulating the carrier concentration. In this work, a series of PbSe(NaCl)x (x = 3, 3.5, 4, 4.5) samples were synthesized through the NaCl salt-assisted approach with Na+ and Cl- doped into their lattice. Both theoretical and experimental results demonstrate that manipulating the carrier concentration by adjusting the content of NaCl is conducive to upgrading the electrical transport properties of the materials. The carrier concentration elevated from 2.71 × 1019 cm-3 to 4.16 × 1019 cm-3, and the materials demonstrated a maximum power factor of 2.9 × 10-3 W m-1 K-2. Combined with an ultralow lattice thermal conductivity of 0.7 W m-1 K-1, a high thermoelectric figure of merit (ZT) with 1.26 at 690 K was attained in PbSe(NaCl)4.5. This study provides a guideline for chemical doping to improve the thermoelectric properties of PbSe further and promote its applications.
2D/3D perovskite heterojunctions exhibit promising prospects in the improvement of efficiency and stability of perovskite solar cells (PSCs). However, many challenges remain in the development of high-quality 2D/3D heterojunctions, such as a reliable pathway to control the perovskite phase and generally poor performance in inverted (p-i-n) devices, which limit their commercialization. Fortunately, many excellent works have proposed lots of strategies to solve these challenges, which have triggered a new wave of research on 2D/3D perovskite heterojunctions in recent years. In this paper, the latest research progress and the critical factors involved in the modulating mechanisms of PSCs with 2D/3D heterojunctions have been summarized and laid out systematically. The advantages of constructing 2D/3D perovskite heterojunctions in PSCs are highlighted, and the problems and related solutions of low-dimensional perovskites as passivation layers towards high-performance PSCs are also discussed in depth. Finally, the prospects of 2D/3D perovskite heterojunctions utilized in the passivation strategies to further improve the photovoltaic performance of PSCs in the future have been presented.
In this study, a novel metal oxide, lanthanum nickelate (LNO) with a perovskite structure, was introduced into a polymer solar cell (PSC) device, replacing the PEDOT:PSS hole transport layer (HTL). The results show that the LNO-based PTB7-Th:PC71BM solar cell exhibits a higher circuit current density, power conversion efficiency, and stability compared with a device with PEDOT:PSS HTL. To understand the effect of LNO HTL on the performance of devices, the active layer morphology and charge transport characteristics in PSCs were systematically analyzed. The morphology of active layer was affected by the HTL, which further regulated the generation and transport processes of charge carrier in the PSC device. For the LNO HTL, an appropriate thickness (8 nm) and a small surface roughness (Sq = 0.7 nm) can coordinate the energy-level structure of device and improve the interface contact between the FTO electrode and PTB7-Th:PC71BM active layer, promoting the charge transport performance of device. Therefore, this work provides a new consideration for the preparation of efficient, stable, and low-cost polymer solar cells.
In the development of perovskite solar cells, a new version of Don Quixote is needed if scientists are to keep on seeking the most celebrated works of literature, according to the evaluation criterion of 'THE FIRST' and 'THE BEST'. Perovskite solar cells have developed rapidly in recent years due to several factors, including their high light absorption capability, long carrier lifetime, high defect tolerance, and adjustable band gap. Since they were first reported in 2009, solar cells based on organic-inorganic hybrid halide lead perovskites have achieved a power conversion efficiency of over 23%. However, although there are broad development prospects for perovskite solar cells, their lead toxicity and instability resulting from the use of organic-inorganic hybrid halide lead perovskites such as CH3NH3PbI3 limit their application, which is further deteriorating progressively. Therefore, the development of environmentally friendly, stable and efficient perovskite materials for future optoelectronic applications has long-term practical significance, which can eventually be commercialized. In this case, the discovery and development of inorganic lead-free perovskite light absorbing materials have become an active research topic in the field of photovoltaics. In this review, we discuss the application of organic-inorganic hybrid halide lead perovskites. This application is further analyzed and summarized using the research progress on inorganic lead-free perovskite solar cells by restoring some relevant prospects for the development of inorganic lead-free perovskite solar cells.
In this study, for the first time, we report a solution-processed amino-functionalized copolymer semiconductor (PFN-2TNDI) with a conjugated backbone composed of fluorine, naphthalene diimide, and thiophene spacers as the electron transporting layer (ETL) in n-i-p planar structured perovskite solar cells. Using this copolymer semiconductor in conjunction with a planar n-i-p heterojunction, we achieved an unprecedented efficiency of â¼16% under standard illumination test conditions. More importantly, the perovskite devices using this polymer ETL have shown good stability under constant ultra violet (UV) light soaking during 3000 h of accelerated tests. Various advanced spectroscopic characterizations, including ultra-fast spectroscopy, ultra-violet photoelectron spectroscopy and electronic impedance spectroscopy, elucidate that the interaction between the functional polymer ETL and the perovskite layer plays a critical role in trap passivation and thus, the device UV-photostability. We expect that these results will boost the development of low temperature solution-processed organic ETL materials, which is essential for the commercialization of high-performance and stable, flexible perovskite solar cells.
