Anion Confinement for Homogeneous Mixed Halide Perovskite Film Growth by Electrospray.

Wide-bandgap perovskites are promising absorbers for state-of-the-art tandem solar cells to feasibly surpass Shockley-Queisser limit with low cost. However, the commonly used mixed halide perovskites suffer from poor stability; particularly, photoinduced phase segregation. Electrospray deposition is developed to bridge the gap of growth rate between iodide and bromide components during film growth by spatially confining the anion diffusion and eliminating the kinetic difference, which universally improves the initial homogeneity of perovskite films regardless of device architectures. It thus promotes the efficiency and stability of corresponding solar cells based on wide-bandgap (1.68 eV) absorbers. Remarkable power conversion efficiencies (PCEs) of 21.44% and 20.77% are achieved in 0.08 cm2 and 1.0 cm2 devices, respectively. In addition, these devices maintain 90% of their initial PCE after 1550 h of stabilized power output (SPO) tracking upon one sun irradiation (LED) at room temperature.

Gelation of Hole Transport Layer to Improve the Stability of Perovskite Solar Cells.

To achieve high power conversion efficiency (PCE) and long-term stability of perovskite solar cells (PSCs), a hole transport layer (HTL) with persistently high conductivity, good moisture/oxygen barrier ability, and adequate passivation capability is important. To achieve enough conductivity and effective hole extraction, spiro-OMeTAD, one of the most frequently used HTL in optoelectronic devices, often needs chemical doping with a lithium compound (LiTFSI). However, the lithium salt dopant induces crystallization and has a negative impact on the performance and lifetime of the device due to its hygroscopic nature. Here, we provide an easy method for creating a gel by mixing a natural small molecule additive (thioctic acid, TA) with spiro-OMeTAD. We discover that gelation effectively improves the compactness of resultant HTL and prevents moisture and oxygen infiltration. Moreover, the gelation of HTL improves not only the conductivity of spiro-OMeTAD, but also the operational robustness of the devices in the atmospheric environment. In addition, TA passivates the perovskite defects and facilitates the charge transfer from the perovskite layer to HTL. As a consequence, the optimized PSCs based on the gelated HTL exhibit an improved PCE (22.52%) with excellent device stability.

Engineering Amorphous-Crystallized Interface of ZrNx Barriers for Stable Inverted Perovskite Solar Cells.

It is challenging to achieve long-term stability of perovskite solar cells due to the corrosion and diffusion of metal electrodes. Integration of compact barriers into devices has been recognized as an effective strategy to protect the perovskite absorber and electrode. However, the difficulty is to construct a thin layer of a few nanometers that can delay ion migration and impede chemical reactions simultaneously, in which the delicate microstructure design of a stable material plays an important role. Herein, ZrNx barrier films with high amorphization are introduced in p-i-n perovskite solar cells. To quantify the amorphous-crystalline (a-c) density, pattern recognition techniques are employed. It is found the decreasing a-c interface in an amorphous film leads to dense atom arrangement and uniform distribution of chemical potential, which retards the interdiffusion at the interface between ions and metal atoms and protect the electrodes from corrosion. The resultant solar cells exhibit improved operational stability, which retains 88% of initial efficiency after continuous maximum power point tracking under 1-Sun illumination at room temperature (25 °C) for 1500 h.

Inhibited Crack Development by Compressive Strain in Perovskite Solar Cells with Improved Mechanical Stability.

Metal halide perovskites are promising as next-generation photovoltaic materials, but stability issues are still a huge obstacle to their commercialization. Here, the formation and evolution of cracks in perovskite films during thermal cycling, which affect their mechanical stability, are investigated. Compressive strain is employed to suppress cracks and delamination by in situ formed polymers with low elastic modulus during crystal growth. The resultant devices pass the thermal-cycling qualification (IEC61215:2016), retaining 95% of the initial power conversion efficiency (PCE) and compressive strain after 230 cycles. Meanwhile, the p-i-n devices deliver PCEs of 23.91% (0.0805 cm2 ) and 23.27% (1 cm2 ). The findings shed light on strain engineering with respect to their evolution, which enables mechanically stable perovskite solar cells.

Avoiding Structural Collapse to Reduce Lead Leakage in Perovskite Photovoltaics.

Perovskite solar cells (PSCs) have become a promising candidate for the next-generation photovoltaic technologies. As an essential element for high-efficiency PSCs however, the heavy metal Pb is soluble in water, causing a serious threat to the environment and human health. Due to the weak ionic bonding in three-dimensional (3D) perovskites, drastic structure decomposition occurs when immersing the perovskite film in water, which accelerates the Pb leakage. By introducing the chemically stable Dion-Jacobson (DJ) 2D perovskite at the 3D perovskite surface, the film dissolution is significantly slowed down, which retards lead leakage. As a result, the Pb contamination is dramatically reduced under various extreme conditions. In addition, the PSCs device deliver a power conversion efficiency (PCE) of 23.6 % and retain over 95 % of their initial PCE after the maximum power point tracking for over 1100 h.

Electron-Deficient and Quinoid Central Unit Engineering for Unfused Ring-Based A1 -D-A2 -D-A1 -Type Acceptor Enables High Performance Nonfullerene Polymer Solar Cells with High Voc and PCE Simultaneously.

Here, a pair of A1 -D-A2 -D-A1 unfused ring core-based nonfullerene small molecule acceptors (NF-SMAs), BO2FIDT-4Cl and BT2FIDT-4Cl is synthesized, which possess the same terminals (A1 ) and indacenodithiophene unit (D), coupling with different fluorinated electron-deficient central unit (difluorobenzoxadiazole or difluorobenzothiadiazole) (A2 ). BT2FIDT-4Cl exhibits a slightly smaller optical bandgap of 1.56 eV, upshifted highest occupied molecular orbital energy levels, much higher electron mobility, and slightly enhanced molecular packing order in neat thin films than that of BO2FIDT-4Cl. The polymer solar cells (PSCs) based on BT2FIDT-4Cl:PM7 yield the best power conversion efficiency (PCE) of 12.5% with a Voc of 0.97 V, which is higher than that of BO2FIDT-4Cl-based devices (PCE of 10.4%). The results demonstrate that the subtle modification of A2 unit would result in lower trap-assisted recombination, more favorable morphology features, and more balanced electron and hole mobility in the PM7:BT2FIDT-4Cl blend films. It is worth mentioning that the PCE of 12.5% is the highest value in nonfused ring NF-SMA-based binary PSCs with high Voc over 0.90 V. These results suggest that appropriate modulation of the quinoid electron-deficient central unit is an effective approach to construct highly efficient unfused ring NF-SMAs to boost PCE and Voc simultaneously.