Eliminating Resistance-Capacitance Coupling Shielding for Depicting the Defect Landscape in Perovskite Solar Cells by Capacitance Spectroscopy.

Capacitance spectroscopy techniques have been widely utilized to evaluate the defect properties in perovskites, which contribute to the efficiency and operation stability development for perovskite solar cells (PSCs). Yet the interplay between the charge transporting layer (CTL) and the perovskite on the capacitance spectroscopy results is still unclear. Here, they show that a pseudo-trap-state capacitance signal is generated in thermal admittance spectroscopy (TAS) due to the enhanced resistance capacitance (RC) coupling caused by the carrier freeze-out of the CTL in PSCs, which could be discerned from the actual defect-induced trap state capacitance signal by tuning the series resistance of PSCs. By eliminating the RC coupling shielding effect on the defect-induced capacitance spectroscopy, it is obtain the actual defect density which is 4-folds lower than the pseudo-trap density, and the spatial distribution of defects in PSCs which reveals that the commonly adopted interface passivators can passivate the defects about 60 nm away from the decorated surface. It is further revealed that phenethylammonium ions (PEA+) possess a better passivation capability over octylammonium ions (OA+) due to the deeper passivation depth for PEA+ on the surface defects in perovskite films.

Visualizing the Structure-Property Nexus of Wide-Bandgap Perovskite Solar Cells under Thermal Stress.

Wide-bandgap perovskite solar cells (PSCs) toward tandem photovoltaic applications are confronted with the challenge of device thermal stability, which motivates to figure out a thorough cognition of wide-bandgap PSCs under thermal stress, using in situ atomic-resolved transmission electron microscopy (TEM) tools combing with photovoltaic performance characterizations of these devices. The in situ dynamic process of morphology-dependent defects formation at initial thermal stage and their proliferations in perovskites as the temperature increased are captured. Meanwhile, considerable iodine enables to diffuse into the hole-transport-layer along the damaged perovskite surface, which significantly degrade device performance and stability. With more intense thermal treatment, atomistic phase transition reveals the perovskite transform to PbI2 along the topo-coherent interface of PbI2/perovskite. In conjunction with density functional theory calculations, a mutual inducement mechanism of perovskite surface damage and iodide diffusion is proposed to account for the structure-property nexus of wide-bandgap PSCs under thermal stress. The entire interpretation also guided to develop a thermal-stable monolithic perovskite/silicon tandem solar cell.

Tandem Electro-Oxidative C-C and C-N Coupling and Aromatization for the Construction of Pyrazine-Fused Bis-aza[7]helicene.

Repeated tandem electro-oxidative C-C and C-N coupling and aromatization were employed for the efficient construction of aza[7]helicene (BA7) as a key intermediate and the targeted pyrazine-fused bis-aza[7]helicene (PBBA7) derivatives in 90.0-93.2% isolated yields under a controlled potential. The electrosynthetic protocol showed high selectivity and enabled rapid access to functionalized organic conjugated materials from readily available polycyclic aromatic amines. A synthetic mechanistic study along with an investigation of the photoelectrical properties and application of PBBA7-C16 as a potential hole-transporting material for perovskite solar cells were performed.

Phase-Stable Wide-Bandgap Perovskites for Four-Terminal Perovskite/Silicon Tandem Solar Cells with Over 30% Efficiency.

Wide-bandgap perovskite solar cells (PSCs) with an optimal bandgap between 1.7 and 1.8 eV are critical to realize highly efficient and cost-competitive silicon tandem solar cells (TSCs). However, such wide-bandgap PSCs easily suffer from phase segregation, leading to performance degradation under operation. Here, it is evident that ammonium diethyldithiocarbamate (ADDC) can reduce the detrimental I2 back to I- in precursor solution, thereby reducing the density of deep level traps in perovskite films. The resultant perovskite film exhibits great phase stability under continuous illumination and 30-60% relative humidity conditions. Due to the suppression of defect proliferation and ion migration, the PSCs deliver great operation stability which retain over 90% of the initial power conversion efficiency (PCE) after 500 h maximum power point tracking. Finally, a highly efficient semitransparent PSC with a tailored bandgap of 1.77 eV, achieving a PCE approaching 18.6% with a groundbreaking open-circuit voltage (VOC ) of 1.24 V enabled by ADDC additive in perovskite films is demonstrated. Integrated with a bottom silicon solar cell, a four-terminal (4T) TSC with a PCE of 30.24% is achieved, which is one of the highest efficiencies in 4T perovskite/silicon TSCs.

Stabilizing Fullerene for Burn-in-Free and Stable Perovskite Solar Cells under Ultraviolet Preconditioning and Light Soaking.

It is crucial to make perovskite solar cells sustainable and have a stable operation under natural light soaking before they become commercially acceptable. Herein, a small amount of the small molecule bathophenanthroline (Bphen) is introduced into [6,6]-phenyl-C61 -butyric acid methyl ester and it is found that Bphen can stabilize the C60 -cage well through formation of much more thermodynamically stable charge-transfer complexes. Such a strengthened complex is used as an interlayer at the in-light perovskite/SnO2 side to achieve a champion device with efficiency of 23.09% (certified 22.85%). Most importantly, the stability of the resulting devices can be close to meeting the requirements of the International Electrotechnical Commission 61215 standard under simulated UV preconditioning and light-soaking testing. They can retain over 95% and 92% of their initial efficiencies after 1100 h UV irradiation and 1000 h continuous illumination of maximum power point tracking at 60 °C, respectively.