Abstract
The mesoporous (meso)-TiO2 layer is a key component of high-efficiency perovskite solar cells (PSCs). Herein, pore size controllable meso-TiO2 layers are prepared using spin coating of commercial TiO2 nanoparticle (NP) paste with added soft polymer templates (SPT) followed by removal of the SPT at 500 °C. The SPTs consist of swollen crosslinked polymer colloids (microgels, MGs) or a commercial linear polymer (denoted as LIN). The MGs and LIN were comprised of the same polymer, which was poly(N-isopropylacrylamide) (PNIPAm). Large (L-MG) and small (S-MG) MG SPTs were employed to study the effect of the template size. The SPT approach enabled pore size engineering in one deposition step. The SPT/TiO2 nanoparticle films had pore sizes > 100 nm, whereas the average pore size was 37 nm for the control meso-TiO2 scaffold. The largest pore sizes were obtained using L-MG. SPT engineering increased the perovskite grain size in the same order as the SPT sizes: LIN < S-MG < L-MG and these grain sizes were larger than those obtained using the control. The power conversion efficiencies (PCEs) of the SPT/TiO2 devices were ∼20% higher than that for the control meso-TiO2 device and the PCE of the champion S-MG device was 18.8%. The PCE improvement is due to the increased grain size and more effective light harvesting of the SPT devices. The increased grain size was also responsible for the improved stability of the SPT/TiO2 devices. The SPT method used here is simple, scalable, and versatile and should also apply to other PSCs.
Highlights
The power conversion efficiency (PCE) of perovskite solar cells (PSC) has increased from 3.8% in 20091 to 25.2%,2 which is exceptional
PNIPAm was selected as the template polymer because it is soluble in EtOH, which is a key solvent used in TiO2 pastes.[8,22,40]
The average diameters for L-MG, S-MG, and linear polymer (LIN) obtained from Scanning electron microscopy (SEM)
Summary
The power conversion efficiency (PCE) of perovskite solar cells (PSC) has increased from 3.8% in 20091 to 25.2%,2 which is exceptional. The PCE of PSCs and other solar cells[12] has been increased through pore size engineering of mesoTiO2.13−1513−15 A seminal study by Hwang et al used polystyrene (PS) particles as templates to include wellcontrolled pores within meso-TiO2 layers for PSCs.[13]. We aimed to use a polymer that was in the soft (swollen) state and as many commercial ingredients as possible to provide a simple and versatile templating method for improving the control of meso-TiO2 pore size using pore size engineering. We hypothesized that increasing the meso-TiO2 pore size would increase perovskite (PVK) grain size and PCE
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