Low Temperature Processed SnO₂ Electron Transporting Layer from Tin Oxalate for Perovskite Solar Cells

Abstract

SnO2 has been widely recognized as an indispensable electron transporting layer for perovskite solar cells. Therefore, a lot of research interest has been paid to fabricate low temperature flexible perovskite solar cells using SnO2 electron transporting layers. Previous solution processed low temperature SnO2 electron transporting layers usually rely on presynthesized SnO2 nanocrystals or complicated post-treatments, which are quite expensive. Herein, we have demonstrated a facile solution processed method for depositing SnO2 electron transporting layers at a low temperature of 100 °C using tin oxalate and hydrogen peroxide. We find that a low volume of hydrogen peroxide is critical for depositing SnO2 electron transporting layers with superior film quality. After optimizing the hydrogen peroxide volume, perovskite solar cells using our SnO2 electron transporting layer can demonstrate a champion performance of 21.32%; at the same time, the perovskite solar cell can maintain 99.0% of its initial power conversion efficiency after storage for 60 days. Therefore, our method has great potential to be applied in flexible PSCs in the future.

Surface Passivation of Perovskite Solar Cells with Oxalic Acid: Increased Efficiency and Device Stability

“…The current‐voltage curves measured in dark condition for electron only devices are shown in Figure 4a. The kink points in the current‐voltage curves correspond to the trap‐filling limited voltages (V TFL s), which are closely related to the defect densities (N d ) in the perovskite films through equation N d =2ϵ 0 ϵV TFL /(eL 2 ) [20,28] . From Figure 4a, the V TFL for perovskite films without and with 0.75 mg mL −1 H 2 C 2 O 4 post‐treatment are determined to be 1.414 V and 1.180 V respectively.…”

“…The kink points in the current-voltage curves correspond to the trap-filling limited voltages (V TFL s), which are closely related to the defect densities (N d ) in the perovskite films through equation N d = 2ɛ 0 ɛV TFL / (eL 2 ). [20,28] From Figure 4a, the V TFL for perovskite films without and with 0.75 mg mL À 1 H 2 C 2 O 4 post-treatment are determined to be 1.414 V and 1.180 V respectively. Correspondingly, the defect densities are 2.52×10 16 cm À 3 and 2.10×10 16 cm À 3 for perovskite films without and with 0.75 mg mL À 1 H 2 C 2 O 4 posttreatment respectively.…”

“…For surface defect passivation, perovskite films are post-treated with these H 2 C 2 O 4 solutions via spin-coating (4000 rpm, 30 s), then the H 2 C 2 O 4 passivated perovskite films are further thermally-treated at 150 °C for 10 min. Spiro-OMeTAD solution is prepared according to our previous studies, and deposited onto the perovskite films at 4000 rpm for 30 s. [28,33] Finally, metal Ag electrode is prepared via thermal evaporation.…”

“…The SnO 2 precursor is obtained by addition of 155 mg tin oxalate into 250 μL H 2 O 2 and 750 μL deionized water according to our previous studies. [28,33] Two-step deposition method is used to fabricate the perovskite films according to our previous reports. [28,33] In brief, 300 mg PbI 2 is added into 0.5 mL DMF/DMSO (95 : 5, v/v) solvent, and stirred overnight before use.…”

“…[28,33] Two-step deposition method is used to fabricate the perovskite films according to our previous reports. [28,33] In brief, 300 mg PbI 2 is added into 0.5 mL DMF/DMSO (95 : 5, v/v) solvent, and stirred overnight before use. The filtered PbI 2 precursor is deposited onto the SnO 2 layer via spin-coating (1500 rpm, 30 s), then thermally-treated at 70 °C for 1 min.…”