Vapour-based processing of hole-conductor-free CH₃NH₃PbI₃ perovskite/C₆₀ fullerene planar solar cells

Abstract

A new sequential-vapour-deposition method is demonstrated for the growth of high-quality CH 3 NH 3 PbI 3 perovskite films. This has enabled the all-vapour, low-temperature fabrication of hole-conductor-free planar perovskite solar cells consisting of only a CH 3 NH 3 PbI 3 /C 60 bilayer sandwiched between two electrical contacts, with a power conversion efficiency of 5.4%.Organometallic trihalide perovskites with the general formula (RNH 3 )MeX 3 (where R is an organic group, Me is Pb or Sn, and X is a halogen I, Br, or Cl) have recently emerged as new generation light harvesting materials in excitonic solar cells.1-3 In particular, methylammonium (MA) lead triiodide (CH 3 NH 3 PbI 3 or MAPbI 3 ) has attracted great deal of attention since it was rst applied as the light absorber in mesoscopic solar cells.4-6 Within a short period of time the power conversion efficiency (PCE) of MAPbI 3 -based solar cells has shot up dramatically to 16.2%. 4,6,7 This rapid rise in the performance is the result of the innate desirable properties of MAPbI 3 , including favourable direct band gap, large adsorption coefficient, high carrier mobilities and long carrier (balanced) diffusion lengths. 1,5,6,8 With regards to the latter, Xing et al.8 showed that the carrier diffusion length in solution-processed MAPbI 3 thin lms is at least 100 nm, despite the non-ideal nature of the solution-spun MAPbI 3 lms. Higher PCEs of $12% were obtained by Malinkiewicz et al. 9 and Chen et al.10 in planar (non-mesoscopic) solar cells based on better quality MAPbI 3 lms of $300 nm thickness. This suggests that maximizing the quality (coverage, crystallinity, texture) of MAPbI 3 lms can lead to carriers diffusion lengths >300 nm, which is the key to realizing planar perovskite-based solar cells with high efficiencies. 8,9However, reliable deposition of high-quality lms of phasepure MAPbI 3 perovskites with full coverage and high crystallinity still remains a challenge.5,6 One-step solution-spun MAPbI 3 generally results in lms with pinholes due to high reaction rate between MAI and PbI 2 .4,10 To address this issue Burschka, et al.4 developed a two-step method, where mesoporous TiO 2 is rst inltrated by solution-processed PbI 2 , followed by dipping it in a MAI solution for the in situ formation of MAPbI 3 . However, in the case of planar solar cells, where a mesoporous TiO 2 scaffold is not used, several hours are needed for the complete conversion of MAPbI 3 , which can result in the peeling of the lms.4 In another study involving planar solar cells, the dipping process was replaced by extended annealing of the solution-processed PbI 2 lm in a MAI-vapour-rich N 2 atmosphere at 150 C. 10 However, this process may be not amenable to producing uniform MAPbI 3 lms on organic substrates.10 Meanwhile, Liu et al. 11 and Malinkiewicz et al. 9used dual-source co-evaporation deposition to prepare uniform, pinhole-free lms of MAPbI 3 or chorine-doped MAPbI 3 , where the resulting planar solar cells delivered one of the highest PCEs. However, car...

Hole transporting material-free and annealing-free thermal evaporated planar perovskite solar cells with an ultra-thin CH3NH3PbI3−Cl layer

“…The device shows a J SC , V OC , FF, and PCE of 14.83 mA/cm 2 , 0.79 V, 0.72, and 8.37%, respectively. To the best of our knowledge, this is the highest PCE for thermal-evaporated HTM-free perovskite solar cells with a perovskite layer deposited directly on TCOs [26,27]. Moreover, such a PCE is comparable and even a slight higher than some other recently reported HTM-free perovskite solar cells despite that an ultra-thin CH 3 NH 3 PbI 3ÀX Cl X layer is used here [21][22][23][24].…”

“…Tsai et al [25] fabricated an inverted HTM-free PHJ perovskite solar cell with a PCE of 11.02% by a solution process. Hu et al [26] demonstrated an inverted HTM-free PHJ perovskite solar cell with a simple thermal evaporated perovskite/C 60 bilayer structure, which presented a PCE of 5.4%. Ng et al [27] reported that the PCE can be increased to 6.1% via adopting 4,7-diphenyl-1,10-phenanthroline (Bphen) as the hole blocking layer.…”

“…Perovskite films can be prepared by solution process via one-step or two-step solution depositions [2,3] and vacuum thermal evaporation [4,[26][27][28]. Among these methods, the vacuum thermal evaporation forms a perovskite film with the most homogeneous morphology and the highest coverage, leading to a higher PCE of the corresponding devices.…”

Two-dimensional organic-inorganic hybrid perovskite: from material properties to device applications

“…As a result, dense and uniform perovskite films with increased grain size can be obtained after subsequent annealing. Besides one-step solution process, vapour deposition methods [71,72] and spraydeposition [26] were proposed. Perovskite films prepared by the vapour deposition methods are uniform and smooth with continuous coverage and excellent crystallinity.…”

A simple approach for the fabrication of perovskite solar cells in air

“…Other strategies to produce the active layer are based on MAPbX 3 deposition using vapor techniques, where the perovskite growth is carried out without using any solvent. In fact, several different vapor deposition techniques are reported in literature, showing better film uniformity and surface coverage of the active layer compared to the solution processed films [18,25]. However vapor deposition has some problems as the source temperature must be tightly controlled due to the relatively low thermal stability of the perovskite precursors.…”