Effects of gas blowing condition on formation of mixed halide perovskite layer on organic scaffolds
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Perovskite solar cells are promising for realizing high power conversion efficiency (PCE) with low manufacturing costs, but efficient coating methods are needed for commercialization. Here, a gas blowing method was used to fabricate perovskite solar cells and was found to create a smooth perovskite layer and to prevent voids in large-area cells, when organic materials were used as scaffolds for forming the perovskite. A PCE of 13% in a 1 cm2 active area is achieved by tuning the band-gap energy of MAPbX3 via substitution of Br for I ions in X sites. Incorporation of a poly(3,4-ethylenedioxythiophene) hole transport layer with a higher work function increased the open circuit voltage of the solar cells. All layers of the cells were fabricated at low temperatures (,140 °C), which makes it possible to incorporate a polymer substrate for producing flexible solar cells and high-throughput fabrication.
I. INTRODUCTION
Recently, organic and inorganic perovskite structures have emerged as efficient absorbers for solar cells. Although their power conversion efficiency (PCE) was around 4% in 2008,1 values exceeding 20% have now been achieved.2 The theoretical limit is estimated to be around 30%, which is superior to silicon solar cells.3 Furthermore, perovskite materials are expected to be suitable as absorbers for tandem solar cells.4 Accordingly, perovskite solar cells have attracted the attention of many researchers. In particular, the ability to form perovskite structures by solution processing offers advantages for low-cost manufacturing. In the past, many methods have been proposed for obtaining high PCEs including the one-step method, two-step method, and antisolvent method,5–7 and in 2014, the gas blowing method was reported as a suitable method.8 The method was applied to the formation of perovskite on TiOx because the focus was on the mesoporous structure of solar cells, and it was reported that the method increased the PCE of only this type of perovskite solar cell. There are three main types of perovskite solar cell structures (mesoporous structure, planar structure, and inverted structure).9 The mesoporous structure is the most wellknown structure because perovskite solar cells originated from dye-sensitized solar cells. In this structure, a PCE of 20.2% has been reported for an active area of 1 cm2.10
Contributing Editor: Sam Zhang a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.264
However, this structure basically requires high process temperatures to form the electron transport layer (ETL) and the mesoporous TiOx (mp-TiOx). Early works reported the planar structure and inverted structure as new types of structures that did not use mp-TiOx, and this allowed perovskite solar cells to be made using low process temperatures. For the planar structure, Miyasaka’s group achieved a PCE of 14% by replacing the ETL with a material that can be created using low process temperatures,11 and they demonstrated flexible perovskite solar cells using this structure. The
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