Cs(2)AgBiBr(6 )having a double perovskite structure is expected to be used in nonlead and stable optoelectronic devices and has received wide attention recently. At this stage, structures of optoelectronic devices using double perovskite and hybrid perovskite are the same. And the energy band structures of double perovskite and hybrid perovskite are different, which will cause energy-level mismatch in the device with double perovskite, which in turn will seriously restrict further improvement of the device performance. A strategy to solve this problem by constructing energy-level gradients with poly(3-hexylthiophene) (P3HT)/MoO3/poly[bis(4-phenyl)(2,4,6-trimethylphenyo-amine] (PTAA) was reported for the first time. The construction of energy-level gradient is mainly achieved by P3HT and PTAA. MoO3 plays a role in protecting the substrate (P3HT) and does not hinder hole transport because it is itself a p-type semiconductor. The champion power conversion efficiency of devices with P3HT/MoO3/PTAA is improved by more than a quarter compared to the standard devices. Moreover, in the champion device, the power conversion efficiency achieved 1.94% with a short-circuit current of 2.80 mA/cm(2).

High-efficiency perovskite solar cells (PSCs) have experienced rapid development and attracted significant attention in recent years. The PSCs based on doctor bladed or slot-die coated perovskite films usually have lower power conversion efficiency (PCE) than that based on spin-coated perovskite films. In this work, we have developed an effective method, called glass rod-sliding and low pressure assisted solution processing composition engineering (GRS-LPASP), to manufacture high quality perovskite film in air. GRS-LPASP composition engineering effectively increases the grain size and thickness of perovskite films and reduces the defect density by increasing the contact area between the perovskite layer and the hole transport layer, thus leading an increased current density (Jsc) of perovskite solar cells. The device with GRS-LPASP composition engineering achieves a maximum PCE of 19.78%. The experimental results demonstrates that GRS-LPASP composition engineering is a feasible method to prepare high-efficiency PSCs. Moreover, GRS-LPASP composition engineering also provides a potential approach for the commercial production of PSCs.

Perovskite solar cells have attracted great research interest as a promising candidate for silicon solar cells. Plenty of work has been reported to use perovskites to semitransparent windows and transparent photovoltaic (TPV) devices to obtain multifunctional systems. However, the narrow bandgap and sharp absorption edge of the typical perovskites prevent them from achieving the highest transparency to satisfy the requirements of aesthetic and integration, and the poor stability and toxic Pb compositions hinder their practical application. Herein, lead-free halide double perovskites with a wide bandgap and indirect bandgap characteristics is introduced to fabricate long-term stable transparent photovoltaic devices exhibiting high visible transmittance (73%) and considerable energy conversion efficiency (1.56%). Through further theoretical calculation and evaluation, a new strategy using indirect bandgap material on TPV devices is proposed to combine the enhancement of these two parameters. This approach will be a significant compliment to near-infrared-absorbing solar cells to selectively harvest light in the invisible region to obtain highly performing multi-junction smart windows on buildings, vehicles and mobile electronics, providing a new reasonable idea to realize TPVs with high efficiency and transparency simultaneously.

The electron-transporting materials (ETMs), 2,7-bis(3,5-di (pyridin-3-yl)phenyl)-9,9'-spirobi [fluorene] (3-4PySF) and 2,7-bis(3,5-di (pyridin-4-yl)phenyl)-9,9'-spirobi [fluorene] (4-4PySF) were designed and synthesized by combining spirobifluorene moiety with di(pyridine-3-yl)phenyl and di(pyridine-4-yl)phenyl, respectively. The spimbifluorene moiety improves materials' rigid twisted structure to ensure the morphological stability of amorphous film, and pyridine acts as electron acceptor to enhance electron-transporting ability of materials. The dependence of electron-transporting property on the position of substituted pyridine rings was studied. The melting point (T-m) of 4-4PySF is estimated to be 41 degrees C higher than that of 3-4PySF. And the higher current density in the electron only devices exhibited by 4-4PySF revealed the effect of nitrogen atom position on the charge-transporting properties. Green PhOLEDs based on bis(2-phenylpyridine)iridium (III) (2,2,6,6-tetramethylheptane-3,5-diketonate) (Ir (ppy)(2)tmd) as the emitter and 3-4PySF, 4-4PySF and 1,3,5-tris(N-phenylbenzimid azol-2-yl-benzene (TPBi) as ETMs were fabricated. Compared to the device based on the conventional ETM TPBi, the devices based on new ETMs exhibited a higher maximum external quantum efficiency (EQE) of 20.5% and a lower turn-on voltage (V-on) of 2.6 V.

A semitransparent perovskite solar cell (PSC) with a dielectric/metal/dielectric (DMD) multilayer film as the top transparent electrode is investigated. Through adjusting the thickness and the deposition rate of Ag and WO3 layers, a transparent electrode with a low sheet resistance of 7 omega sq(-1) and high average visible transmittance (AVT) of 73% in the visible wavelength range of 400-800 nm is obtained. Using the resultant DMD film as the top transparent electrode and different bandgap perovskites of CH3NH3PbI3 (MAPbI(3)), CH(NH2)(2)PbI3 (FAPbI(3)), and FA(0.5)MA(0.38)Cs(0.12)PbI(2.04)Br(0.96) as the optical active layer, a solar cell with a device architecture of ITO/SnO2/perovskite/spiro-OMeTAD/MoO3/Ag/WO3 is fabricated. A series of efficient semitransparent PSCs with high transmittance are achieved.

Lead-based organic-inorganic hybrid perovskite materials are widely used in optoelectronic devices due to their excellent photophysical properties. However, the main issues which hinder its commercialization are the toxicity caused by lead and the intrinsic instability of the material. Recently, many lead-free halide materials with good intrinsic stability have been reported, among which bismuth-based halide materials have attracted extensive research due to their structure and promising optoelectronic properties. In this review, bismuth-based materials are divided into binary BiX3 (X = I, Br, Cl), ternary A(a)Bi(b)X(a)(+3)(b) (A = Cs, Rb, MA, Ag, etc.), and quaternary A(2)AgBiX(6) (A = Cs, Rb, MA, etc.) according to its elemental composition. The structure and optoelectronic properties of bismuth-based halide materials, which may be helpful for the development of bismuth-based halide materials and lead-free perovskites in the future, are summarized and highlighted.