Stabilizing and scaling up carbon-based perovskite solar cells
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Shihe Yangb) Department of Chemistry, The Hong Kong University of Science and Technology, Kowloon, Hong Kong, China (Received 25 April 2017; accepted 30 June 2017)
Organometal trihalide perovskite solar cells (PSCs) have sparked a frantic excitement in the scientific community because they can achieve high power conversion efficiencies (PCEs) even when fabricated by low-cost solution-processing technologies. However, the poor stability of PSCs has seriously hindered their commercialization. Among various kinds of PSCs, carbon-based PSCs without hole transport materials (C-PSCs) seem to be the most promising for addressing the stability issue because carbon materials are stable, inert to ion migration, and inherently water-resistant. Concurrent with the steady rise in PCE of C-PSCs, great progresses have also been attained on the device stability and scaling-up fabrication of C-PSCs, which have well signified the possible commercialization of PSCs in the near future. In this review, we will summarize these progresses with a view of exposing the promising prospect. We start by collating recent stability testing results of C-PSCs with reference to those of HTM-PSCs. Then, we update the research status on large-scale C-PSCs and their associated scalable fabrication technologies. Finally, we identify main issues to be addressed alongside future research directions.
I. INTRODUCTION
Organometal trihalide perovskite solar cells (PSCs) have attracted wide attention because such a solution process-based photovoltaic device has obtained comparable power conversion efficiencies (PCEs) (over 22%) with traditional commercial solar cells in a short time span of its development.1–12 The special and advantageous optoelectronic properties of the hybrid materials (ABX3: A 5 CH3NH3, HC(NH2)2, Cs; B 5 Pb, Sn; X 5 Cl, Br, I) that account for the rapid growth in PCE,7,13 include high mobility,14–17 long balanced carrier diffusion length,15,16,18,19 and low exciton binding energy.20 Despite the high PCEs and the solution-based processes advantageous in commercializing PSCs, the poor device stability significantly hampered the application. The instability problem is caused not only by the perovskite itself but also by the conventional organic hole transport material (HTM), such as spiro-OMeTAD, PTAA, P3HT. Organic HTM layers are usually open and susceptible to migration of halide ions and metal ions (from the metal electrode), which inevitably result in device degradation.21–27 Besides, most of these organic HTMs are expensive and operationally unstable (usually Contributing Editor: Gary L. Messing Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2017.294
require inert atmosphere). Fortunately, researchers have proved that perovskites (e.g., CH3NH3PbI3) could serve as both a light harvester and a hole transporter,18,19,28,29 thus facilitating HTM-free PSCs.29–34 So far, several types of HTM-free PSCs have been developed with using Au,28,35 Ni,36 or carbon29,37–39 as hol
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