Boosted Charge‐Carrier Transport in Triple‐Cation Perovskites by Ultrasonic Vibration Post Treatment

Abstract

cells and realized a power conversion efficiency (PCE) of 3.8%, rapid improvements in PCE (currently up to 25.5% [2] ) have been achieved. Because of the tunable optical and electronic properties of MHPs combined with facile processing procedures, [3] applications of MHPs are no longer limited to solar cells, but have quickly extended to light-emitting diodes, [4,5] photodetectors, [6][7][8][9] amplified spontaneous emission of lasers, [10][11][12][13] fieldeffect transistors, [14,15] etc. Among all possible combinations in the category of perovskite materials, triplecation perovskites, consisting of cesium (Cs + ), methylammonium (MA + ), and formamidinium (FA + ) cations at A-site in the ABX 3 structure, have gained tremendous attention. Saliba et al. [16] demonstrated that triple-cation perovskites show outstanding stability in photovoltaic devices and reproducibility during the fabrication process. By introducing a small amount of Cs + in MHPs, unstable yellow phase is effectively suppressed, [16] allowing the formation of a more stable black perovskite phase, which resists against humidity and temperature. The performance of solar cells employing the triple-cation perovskites has improved rapidly in the last 5 years. [17][18][19][20] Zhou and co-workers [20] have obtained an outstanding PCE of 21.46% by simultaneously passivating both anion and cation vacancies in the perovskite layer, and the device preserves 90% of the original PCE after 1000 h of operation. Recently, tandem devices combining triple-cation perovskites and c-Si have reached a PCE of >25%. [21] To fabricate solar cells with desirable performance, it is of vital importance to make high-quality perovskite films by controlling the crystallization process. By doing so, the nonradiative recombination is suppressed. Such positive effects have been reported by Gao et al. in the relevant morphology studies on porphyrin-based organic photovoltaics. [22,23] In this regard, multiple strategies have been developed. The traditional methods to control crystallization require a final step by annealing and drying the liquid films at temperatures ranging from 70 to 150 °C, to form a solid film. [24][25][26][27][28] Despite the simplicity of this method, annealing tends to yield films with rough surface and pores, and defects in the crystalline structure. [29] An alternative approach is to partially or fully replace annealing with ultrasonic vibration with nanoscale amplitudes imposed on the thin liquid films during drying.Ultrasonic vibration imposed on the substrate of a drying perovskite solution film has previously been proposed as a nearly annealing-free method to improve film quality and thus the photovoltaic performance for perovskite solar cells. However, an in-depth understanding of the underlying mechanism of the improved film quality via ultrasonic vibration is still lacking. In this work, the effects of substrate vibration post treatment on the carrier lifetime and mobility are studied in triple-cation perovskite films. With 80 s of annealing-free...

High‐Quality Hybrid Perovskite Thin Films by Post‐Treatment Technologies in Photovoltaic Applications

“…After the application of ultrasonic vibration, the trap state emission was suppressed (Figure 16b), implying that the vibration‐induced charge‐carrier transport properties can pave the way for the application of ultrasonic vibration toward perovskite‐based electronic devices. [ 220 ]…”

“…b) Proposed band diagram and emissions affected by ultrasonic substrate vibration posttreatment. Reproduced with permission [220]. Copyright 2022, Wiley-VCH.…”