Bridging the Buried Interface with Piperazine Dihydriodide Layer for High Performance Inverted Solar Cells.

Given that it is closely related to perovskite crystallization and interfacial trap densities, buried interfacial engineering is crucial for creating effective and stable perovskite solar cells. Compared with the in-depth studies on the defect at the top perovskite interface, exploring the defect of the buried side of perovskite film is relatively complicated and scanty owing to the non-exposed feature. Herein, the degradation process is probed from the buried side of perovskite films with continuous illumination and its effects on morphology and photoelectronic characteristics with a facile lift-off method. Additionally, a buffer layer of Piperazine Dihydriodide (PDI2 ) is inserted into the imbedded bottom interface. The PDI2 buffer layer is able to lubricate the mismatched thermal expansion between perovskite and substrate, resulting in the release of lattice strain and thus a void-free buried interface. With the PDI2 buffer layer, the degradation originates from the growing voids and increasing non-radiative recombination at the imbedded bottom interfaces are suppressed effectively, leading to prolonged operation lifetime of the perovskite solar cells. As a result, the power conversion efficiency of an optimized p-i-n inverted photovoltaic device reaches 23.47% (with certified 23.42%) and the unencapsulated devices maintain 90.27% of initial efficiency after 800 h continuous light soaking.

Rinsing Intermediate Phase Strategy for Modulating Perovskite Crystal Growth and Fabricating Highly Efficient and Stable Inverted Solar Cells.

During the fabrication of metal halide perovskite films, polycrystal growth and maturation are largely influenced by high-temperature annealing. However, this process would cause crystals to expand or contract at various depths in the film, leading to microscopic structural deformation and further altering the optoelectronic properties of the perovskite film. Herein, we propose an additional rinsing intermediate phase (RIP) strategy that involves precovering the perovskite film surface with a mixed organic layer prior to high-temperature annealing. The lattice distortion of the microscopic structure brought on by the driving force of the heat field is greatly reduced as a result of the modulation for the upper surface of the intermediate phase film by the rinse layer. This strategy can prepare films with high crystallinity, minor residual stresses, fewer defects, and overall film uniformity. As a result, the modified inverted perovskite solar cell (PSC) achieves a certified power conversion (PCE) of 22.76%. Meanwhile, since the rinse layer is involved in the entire crystal formation process, ion migration and buildup in the device are prevented between the interface. Consequently, the devices still retain 90% of their initial PCE, demonstrating enhanced operational stability after 500 h of operation. This method of modulating the intermediate perovskite state offers an investigation into improving the traditional method of making thin films, which is anticipated to hasten the commercialization of perovskite photovoltaics.

Optimization of a SnO2-Based Electron Transport Layer Using Zirconium Acetylacetonate for Efficient and Stable Perovskite Solar Cells.

SnO2 is a promising material for use as an electron transfer layer (ETL) in perovskite photovoltaic devices due to its suitable energy level alignment with the perovskite, high electron mobility, excellent optical transmission, and low-temperature processability. The development of high-quality SnO2 ETLs with a large coverage and that are pinhole-free is crucial to enhancing the performance and stability of the perovskite solar cells (PSCs). In this work, zirconium acetylacetonate (ZrAcac) was introduced to form a double-layered ETL, in which an ideal cascade energy level alignment is obtained. The surface of the resulting ZrAcac/SnO2 (Zr-SnO2) layer is compact and smooth and had a high coverage of SnO2, which enhances the electron extractability, improves ion blocking, and reduces the charge accumulation at the interface. As a result, the fill factor (FF, 80.99%), power conversion efficiency (PCE, 22.44%), and stability of the Zr-SnO2 device have been significantly improved compared to PSCs with only a SnO2 ETL. In addition, the PCE of the Zr-SnO2 device is maintained at more than 80% of the initial efficiency after 500 h of continuous illumination.

Secondary Grain Growth in Organic-Inorganic Perovskite Films with Ethylamine Hydrochloride Additives for Highly Efficient Solar Cells.

The grain boundaries of perovskite polycrystalline are regarded as a defect region that not only provides carrier recombination sites but also introduces device degradation pathways. Efforts to enlarging the grain size of a perovskite film and reducing its grain boundary are crucial for highly efficient and stable perovskite solar cells (PSCs). Some effective methods that facilitate grain growth are postdeposition thermal annealing and solvent vapor annealing. However, a detailed understanding of grain growth mechanisms in perovskite films is lacking. In this study, perovskite films were prepared by adding ethylamine hydrochloride (EACl) to the precursor solution. This additive strategy promotes a new grain growth mode, secondary grain growth, in perovskite films. Secondary grain growth leads to much larger grains with a high crystallographic orientation. These excellent properties lead to reduced grain boundaries and the densities of boundary defects. The improved film quality results in a prolonged charge-carrier lifetime and a significantly enhanced power conversion efficiency (PCE). Compared with the 18.42% PCE of the control device, the PCE of the device with EACl additives reaches 21.07%.