Revealing the interfacial properties of halide ions for efficient and stable flexible perovskite solar cells.

The severe non-radiative recombination loss caused by SnO2/perovskite interface defects greatly hinders the further improvement of the performance and stability of flexible perovskite solar cells (PSCs). Herein, a series of halides KM (M = F, Cl, Br, I) were inserted as interface layers to modulate the SnO2/perovskite interface. Both experimental and theoretical calculation demonstrated that F- exhibited stronger interface coupling effect between the SnO2 and perovskite than other halide ions (Cl-, Br-, I-). The F- had unique effects in effectively depressing SnO2/perovskite interface defects ascribed to the simultaneous formation of SnF bonds and hydrogen bonds, resulting in reduced non-radiative recombination and improved interfacial contact. In consequence, the champion KF-modified flexible and rigid PSCs delivered outstanding PCE of 18.16 % and 21.36 %, accompanied by the enhanced VOC of 1.14 V and 1.16 V, respectively. Meanwhile, the stability of flexible PSCs was significantly ameliorated after KF modification, and about 84 % of the original efficiency could be retained even after 3000 bending cycles. This work provides a facile and efficient strategy for interface modulation to achieve high-performance and stable flexible PSCs.

High-Performance Planar Perovskite Solar Cells with a Reduced Energy Barrier and Enhanced Charge Extraction via a Na2WO4-Modified SnO2 Electron Transport Layer.

Tin oxide (SnO2) has been commonly used as an electron transport layer (ETL) in planar perovskite solar cells (p-PSCs) because it can be prepared by a low-temperature solution-processed method. However, the device performance has been restricted due to the limited electrical performance of SnO2 and its mismatched energy level alignment with the perovskite absorber. Considering these problems, sodium tungstate (Na2WO4) has been employed to modify the SnO2 ETL. The conduction band minimum of SnO2 increases and the defects at the ETL/perovskite interface decrease by the modification of the SnO2 ETL with Na2WO4, thus reducing the energy barrier between the ETL and perovskite. In addition, the electron extraction ability has been enhanced and the interface recombination between the ETL and perovskite has also been inhibited. As a result, the photovoltaic performance of p-PSCs based on the modified ETL has been improved, and a champion power conversion efficiency of 21.16% has been achieved compared with the control device of 17.30% with an open circuit voltage increased from 1.075 to 1.162 V.

Band Matching Strategy for All-Inorganic Cs2AgBiBr6 Double Perovskite Solar Cells with High Photovoltage.

The lead-free double perovskite has been proven to be one of the promising alternatives to solve the stability and toxicity problems of lead-based organic-inorganic hybrid perovskite solar cells. Here, high-quality Cs2AgBiBr6 double perovskite films with large grains and smooth surface have been prepared through a sequential-vapor-deposition method, and a low-cost and eco-friendly Cu2O film with a suitable energy level and good electrical properties was prepared as an efficient hole transport layer by vacuum vapor deposition for the first time. The Cu2O-based devices achieve a champion power conversion efficiency increasing from 1.03 to 1.52% and an enhancement of photovoltage from 1.083 to 1.198 V compared with their organic counterparts. More importantly, the Cu2O-based devices have excellent stability; they maintained the initial 96% efficiency under environmental conditions after 33 days of unpackaged storage. These results also point out the direction for the further development of these new promising perovskite solar cells.

Will organic-inorganic hybrid halide lead perovskites be eliminated from optoelectronic applications?

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.