Developments of Highly Efficient Perovskite Solar Cells

Conspectus After developmentsin just more than a decade, the power conversionefficiency (PCE) of single junction perovskite solar cells (PSCs)has achieved a record of 26.0%. Such rapid progress of PSCs technologyis mainly attributed to the excellent optoelectronic properties andfacile solution-processed fabrication. Starting from the birth ofPSCs up to present, various methods have been attempted to improvethe performance and/or stability of PSCs. The first perovskite photovoltaicdevices achieved a very low efficiency, attributed to the poor qualityof the perovskite film upon a mesoporous substrate. There then arelarge amounts of work aiming at high-quality light-absorber filmswith pin-free, dense, homogeneous morphology with high crystallinity.Hereafter, the developments of carrier transport materials/layers(CTLs) based on different device structures had become an importantissue. The stable CTLs with excellent electrical properties and matchedenergy levels are desired for efficient and stable PSCs. Besides perovskitefilm growth control and employment of advanced CTLs, the main studiesare mitigation of all kinds of defects in PSCs, including charge trapsin the perovskite bulk, interface defects between the perovskite andadjacent CTLs, and grain boundaries located at dangling bonds as wellas halide loss defects. All of these defects in PSCs can not onlycause nonradiation recombination but also provide an extra pathwayfor ionic migration, which leads to irreversible degradation of theperovskite film. And the very current studies on defects are tryingto push PSCs to industrial application, since the long-term stabilityand high-efficiency count as the same importance for PSCs. There isan apparent fact that the literature about PSC fabrication is basedon different experiment conditions, which gives it poor reproducibility.Herein, the conception and motivation of the studies are more valuable.It is necessary to share the research in detail by individual laboratoriesfor a better communication in this rapidly developed field. It couldbe concluded that there are mainly three steps for PSCs to achievesuch high-efficiency and appreciable stability: 1) modulation of theperovskite film quality; 2) development of desired CTLs for PSCs;3) mitigation of defects in the perovskite bulk and/or interfaces.The three steps are also the basic development track of PSCs. In thisAccount, we will briefly review the milestones in the early periodof PSCs. Then, we will mainly focus on our group and coauthors'representative progress of high-efficiency PSCs, following the abovedevelopment order of PSCs technology. The mechanisms and motivationsof improved efficiency and stability in different stages are discussed.Finally, a comprehensive summary as well as the deep perspectivesof PSCs are proposed. And the future directions of PSCs for practicalapplication are also discussed.