Photovoltaic Devices Using Sublimed Methylammonium Lead Iodide Perovskites: Long‐Term Reproducible Processing

Abstract

Perovskite solar cells (PSCs) are viable sources of efficient and affordable energy that has attracted much interest since their onset in 2009 due to rapidly increasing device power conversion efficiencies (PCEs, currently above 25.6% already). [1] Highquality (poly-)crystalline perovskite films have a combination of desirable properties, mainly high absorption coefficient, high ambipolar charge mobility, and long charge carrier diffusion length. [2] These properties are directly related to the film morphology, stoichiometry, and density of defects in the bulk or at the surface. Hence, to ensure reproducible preparation of PSCs, it is crucial that the perovskite growth during deposition is controllable in a repeatable way independent of batchto-batch purity variations of the precursor salts used. A stable reproducible baseline cell performance is crucial to advance the technology and further optimize the efficiency and stability. Numerous deposition processes are investigated, from solvent-based techniques such as spin coating, blade coating, and solvent engineering to vacuum-based methods, such as thermal vacuum deposition or close space sublimation or even hybrid sequential depositions. [2][3][4][5][6][7][8][9][10][11] Physical vapor deposition (PVD) is a very versatile technique that can be used to grow films of many classes of materials, such as metallic, semiconducting, and insulating films for use in photovoltaics and light-emitting devices, as well as resistors, transparent conductive oxides, corrosion resistant coatings, magnetic films, among many others. This technique is widely used in the optoelectronic/semiconductor industry for being compatible with large area and high throughput, granting high purity and uniformity to the deposited films. [9,[12][13][14][15][16][17] It also allows for the in situ monitoring of the deposition rate using quartz crystal microbalances (QCM), which is important when two precursors are cosublimed and to enable precise thickness control. [12,18] Many research groups have reported on vacuum-deposited perovskites, showing that efficient fully evaporated solar cells are readily achievable. Different perovskite compositions have been prepared ranging from the archetypal MAPbI 3 , requiring the coevaporation of PbI 2 and CH 3 NH 3 I (methylammonium iodide, MAI) in only two sources, [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] to more complex multication multihalide structures that require the coevaporation from three or more precursors. [36][37][38][39][40][41][42][43] There are many examples in the literature of coevaporated MAI-based PSCs with PCEs exceeding 20%. [22,25,[43][44][45][46] However, despite these successful demonstrations, the sublimation control of organic ammonium halides remains a critical factor in achieving reproducibility of the perovskite film in vacuum-processed devices.Many authors have found difficulties in monitoring the MAI sublimation, due to fluctuating deposition rates, [20,22,29,[47][48][49][50][51] or in measuring the thic...

Efficient and Thermally Stable Wide Bandgap Perovskite Solar Cells by Dual‐Source Vacuum Deposition

“…Previous works highlighted the difficulties associated with the sublimation control of MAI, [ 62,63 ] hence we have adopted a recently reported protocol based on a two source/two sensors system, which ensures a reliable and reproducible deposition process. [ 64,65 ] The corresponding Tauc plots obtained from the absorption spectra ( Figure a) show the expected blue‐shift of the absorption cutoff when increasing the bromide contents, leading to wider bandgap perovskites with bandgaps (E g ) of 1.64, 1.68, and 1.71 eV. Photoluminescence (PL) spectra (Figure 1b) also shows the shift of the bandgap with increasing bromide content.…”

Growth methods' effect on the physical characteristics of CsPbBr3 single crystal

“…[1][2][3][4][5] The field of perovskite materials, particularly in photovoltaics, has been extensively studied, with various approaches suggested for improving device efficiency, including enhancements in crystallinity, meticulous interface optimization, and the incorporation of additives. [6][7][8] Perovskite devices exhibit diverse configurations, such as polycrystalline films, single crystals (SCs), nanocrystals, and quantum dots, highlighting the remarkable processability of perovskite materials, supported by their inherent defect tolerance. [9][10][11] Among these configurations, SCs offer advantages over polycrystalline thin films, including higher carrier mobilities and increased environmental resilience.…”

Efficient Metal‐Halide Perovskite Photovoltaic Cells Deposited via Vapor Transport Deposition

“…[17][18][19]21,22] However, the atypical sublimation properties of alkylammonium halides like MAI under high vacuum conditions can result in thermal decomposition, uncontrollable impurity addition, and surface-varied adsorption properties. [23][24][25] In situ monitoring methods [26][27][28] or controlling MAI deposition rate by other processing parameters like chamber pressure [29,30] or substrate temperature [18] have been intensively studied to overcome this challenge.…”