Fabrication of perovskite films using an electrostatic assisted spray technique: the effect of the electric field on morphology, crystallinity and solar cell performance

Abstract

An electric field assisted spray deposition method is employed for improving the perovskite film morphology, crystallinity, and surface coverage, and for further fabricating an efficient solar cell. By applying different voltages ranging from 0.5 to 2.0 kV during spray deposition, we observed a large variation in the film morphology and surface coverage compared to those fabricated without an electric field, which is due to improved atomization from the Coulomb fission process. The optimized applied voltage of 1.5 kV during spraying led to completion of the reaction between CH3NH3I and PbI2 on a hot substrate for pure phase CH3NH3PbI3 thin film formation with improved grain growth and surface coverage. The cells fabricated using perovskite films showed clear applied voltage dependence in the energy conversion process and alleviation in J-V hysteresis; with 1.5 kV applied voltage the average cell efficiency of 8.9% was obtained compared to films fabricated without applying voltage providing only 6.5%. The best efficiencies are 10.9% and 7.37% for applied voltages of 1.5 kV and 0 kV, respectively. The enhancement in efficiency with applied voltage is due to the formation of more uniform and dense films with large perovskite crystals, which resulted in efficient electron transportation (enhanced photocurrent and modified series and shunt resistances) by minimizing the charge carrier recombination at grain boundaries (resulting in enhanced open circuit voltage). With further optimization of the perovskite film thickness by adjusting the CH3NH3I spray volume, the average cell efficiency of ∼11.0% was obtained.

Defect-Free Large-Area (25 cm2) Light Absorbing Perovskite Thin Films Made by Spray Coating

“…This is due to the prolonged crystal growth at low temperatures and therefore the occurrence of crystallization dewetting. Figure 5 shows the range of the substrate temperatures (during the coating process) that have been used in recent published papers [3,7,8,13,16,[18][19][20][21][22]24,25,[30][31][32][33][34][35][36][37], in order to fabricate the perovskite layer of PSCs, mostly by a scalable technique. These techniques include spray coating, doctor blading, slot-die coating, roller coating, inkjet printing, and drop casting.…”

“…Concurrent spraying of perovskite precursors using two spray nozzles is another suggested technique to control the film composition and achieve a pinhole-free film of perovskite [14]. In the literature, spraying of the MAI solution over a pre-cast PbI 2 film in a sequential deposition has been reported, as well [8,18,[21][22][23]. Zabihi et al sprayed perovskite precursor solutions sequentially, using two spray nozzles, on an ultrasonically vibrating substrate to form a mixed halide perovskite film [22].…”

“…For instance, Ramesh et al [7] used a simple airbrush pen to spray CH 3 NH 3 PbI 3 perovskite precursor solution and tuned the ratio of the MAI to PbI 2 precursor solutions, spray flow rate, substrate temperature, and annealing temperature to achieve a desired film. In another work, Chandrasekhar et al used electrostatic spray coating to spray the MAI solution onto a pre-cast PbI 2 film, where a more uniform and dense perovskite film with lager crystals was obtained, compared to that of the conventional spray coating [18]. Heo and coworkers [19] synthesized CH 3 NH 3 PbI 3−x Cl x powder and then dissolved it in a mixture of DMF (dimethylformamide) and GBL (g-butyrolactone).…”

Optimization of spray coating for the fabrication of sequentially deposited planar perovskite solar cells

“…15-20, but has not been adequately explored in the PVSC field, and only a few studies have employed it to fabricate the perovskite layer. [21][22][23][24][25][26][27][28][29][30][31][32][33] Due to the stochastic and random nature of droplet impact, spray-on films normally show a rough surface, 21 but the roughness can be reduced through a process optimization. 22,28 High roughness in spray-on organic SCs was reported to have negative effect on the light absorbance 10 and the device fill factor (FF), 34 although the results obtained for the organic SCs may not be necessarily applicable to crystalline perovskite SCs.…”

Large-area electrospray-deposited nanocrystalline CuXO hole transport layer for perovskite solar cells

“…Although the ultrasonic spray process offers a simple set-up and large-area deposition, the technique lacks control and can lead to impurity incorporation and defect formation. Chandrasekhar 23 reported the electrospray-assisted deposition of perovskite on TiO 2 -coated FTO substrates. This deposition process improved the crystallinity, morphology, and coverage of perovskite lm.…”