Abstract
High-class perovskite film with beautiful surface morphology (such as large-size grain, low defect density, good continuity and flatness) is normally believed to be a very important factor for high-efficiency perovskite solar cells (PSCs). Here, we report a modified sequential deposition route through localized-liquid-liquid-diffusion (LLLD) for qualified perovskite multi-crystalline thin films with micrometer-scaled grains for solar cells. We adopted a contact-type drop method to drop Methylammonium iodide (MAI) solution and have successfully used high-concentration MAI solution (73 mg/mL) to transform PbI2 film into high-class perovskite film via our route. A high efficiency of 10.7% was achieved for the device with spongy carbon film deposited on a separated FTO-substrate as a counter electrode under one sun illumination, which is the highest efficiency (as 2.5 times as previous efficiency) ever recorded in perovskite solar cells with a such spongy carbon/FTO composite counter electrode. The preparation techniques of high-class perovskite thin films under ambient conditions and the cheap spongy carbon/FTO composite counter electrode are beneficial for large-scale applications and commercialization.
Highlights
In recent years, perovskite solar cells (PSCs) have been recognized as the most promising alternative to conventional photovoltaic devices due to their high efficiency and simple process [1–3]
In contrast to the non-contact-type drop method, this drop method reduced the damage of the Methylammonium iodide (MAI) solution to PbI2 thin film according to Figure 1b
The perovskite films were prepared by sequential deposition route with PbI2 0 s, 10 s, and 20 s annealing, which are named as sample A, sample B, and sample C, respectively
Summary
Perovskite solar cells (PSCs) have been recognized as the most promising alternative to conventional photovoltaic devices due to their high efficiency and simple process [1–3]. M. Grätzel et al firstly developed the sequential deposition method (so-called two-step method) to prepare CH3NH3PbI3 perovskite thin films [9]. A lot of effort has been paid to developing the two-step method, similar to the two-step spin-coating process [10–12], and Xu et al have demonstrated that the two-step spin coating method enables perovskite layer morphology to control and fabricate products [13]. Previous researchers prepared perovskite films via the conventional two-step coating method with a necessary step of PbI2 layer annealing [9–13]. We found the properties of the perovskite thin film are very sensitive to the annealing time of PbI2 layer especially under the dry ambient conditions used in our experiments
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