Strain Release and Defect Passivation in Formamidinium-Dominated Perovskite via a Novel in-Plane Thermal Gradient Assisted Crystallization Strategy

Abstract

It is essential to release annealing induced strain during the crystallization process to realize efficient and stable perovskite solar cells (PSCs), which does not seem achievable using the conventional annealing process. Here we report a novel and facile thermal gradient assisted crystallization strategy by simply introducing a slant angle between the preheated hot plate and the substrate. A distinct crystallization sequence resulted along the in-plane direction pointing from the hot side to the cool side, which effectively reduced the crystallization rate, controlled the perovskite grain growth, and released the in-plane tensile strain. Moreover, this strategy enabled uniform strain distribution in the vertical direction and assisted in reducing the defects and aligning the energy bands. The corresponding device demonstrated champion power conversion efficiencies (PCEs) of 23.70% and 21.04% on the rigid and flexible substrates, respectively. These highly stable rigid devices retained 97% of the initial PCE after 1097 h of storage and more than 80% of the initial PCE after 1000 h of continuous operation at the maximum power point. This novel strategy opens a simple and effective avenue to improve the quality of perovskite films and photovoltaic devices via strain modulation and defect passivation.

Green Solvent Polishing Enables Highly Efficient Quasi-2D Perovskite Solar Cells

“…The slopes of the plots are extracted, and the fitted ideality factors are calculated to be 1.05 for the polished film and 1.12 for the unpolished one. The fitted ideality factor approaching 1.0 means less trap-assisted Shockley–Read–Hall recombination. , The dark current density–voltage plot is shown in Figure b. It is clear in the plot that the device with polished film exhibits a low dark current indicating lower leakage current density and a higher rectification ratio .…”

“…The fitted ideality factor approaching 1.0 means less trap-assisted Shockley−Read−Hall recombination. 44,45 The dark current density−voltage plot is shown in Figure 5b. It is clear in the plot that the device with polished film exhibits a low dark current indicating lower leakage current density and a higher rectification ratio.…”

“…The corresponding Nyquist plots are acquired at a constant bias of 1.0 V, as shown in Figure c. The inset is the equivalent circuit, where the R 1 and R 2 represent the series resistance and recombination resistance, respectively . The series resistance is calculated to be 21.65 and 48.55 Ω for the polished device and the control device, respectively.…”

“…The reduction of 32.8 mV of Δ V non‑rad corresponds well with the device performance enhancement in the V oc . Further, the Mott–Schottky model is used to evaluate the built-in potential ( V bi ) of the PSCs . The results are shown in Figure e.…”

“…The inset is the equivalent circuit, where the R 1 and R 2 represent the series resistance and recombination resistance, respectively. 44 The series resistance is calculated to be 21.65 and 48.55 Ω for the polished device and the control device, respectively. The recombination resistance is measured to be 2002 and 1303 Ω for the polished device and the control device, respectively.…”