Many efforts have been made towards improving perovskite (PVK) solar cell stability, but their thermal stability, particularly at 85 °C (IEC 61646 climate chamber tests), remains a challenge. Outdoors, the installed solar cell temperature can reach up to 85 °C, especially in desert regions, providing sufficient motivation to study the effect of temperature stress at or above this temperature (e.g., 100 °C) to confirm the commercial viability of PVK solar cells for industrial companies. In this work, a three-layer printable HTM-free CH NH PbI PVK solar cell with a mesoporous carbon back contact and UV-curable sealant was fabricated and tested for thermal stability over 1500 h at 100 °C. Interestingly, the position of the UV-curing glue was found to drastically affect the device stability. The side-sealed cells show high PCE stability and represent a large step toward commercialization of next generation organic-inorganic lead halide PVK solar cells.

We have prepared perovskite [CH 3 NH 3 PbI 3 (MALI), CH 3 NH 3 PbBr 3 (MALB), NH 2 CH=NH 2 PbI 3 (FALI), and NH 2 CH=NH 2 PbBr 3 (FALB)] thin films by a one-step process on glass/TiO 2 and glass/Al 2 O 3 substrates and studied the stability of the perovskite under UV/visible light radiation up to 24 h at 1.5AM in air. After irradiation, the films were characterized by UV-vis absorption and X-ray diffraction measurements. In addition, photovoltaic performance characteristics in air were studied using different perovskites before (0 h) and after 24 h irradiation. The results revealed that Al 2 O 3 protected the perovskite crystal from degradation. However, the perovskites were unstable except for NH 2 CH=NH 2 PbI 3 under the same conditions using a TiO 2 scaffold layer.

In order to analyze the crystal transformation from hexagonal PbI2 to CH3NH3PbI3 by the sequential (two-step) deposition process, perovskite CH3NH3PbI3 layers were deposited on flat and/or porous TiO2 layers. Although the narrower pores using small nanoparticles prohibited the effective transformation, the porous-TiO2 matrix was able to help the crystal transformation of PbI2 to CH3NH3PbI3 by sequential two-step deposition. The resulting PbI2 crystals in porous TiO2 electrodes did not deteriorate the photovoltaic effects. Moreover, it is confirmed that the porous TiO2 electrode had served the function of prohibiting short circuits between working and counter electrodes in perovskite solar cells.

The CHNHPbI perovskite solar cells have been fabricated using three-porous-layered electrodes as, 〈glass/F-doped tin oxide (FTO)/dense TiO/porous TiO-perovskite/porous ZrO-perovskite/porous carbon-perovskite〉 for light stability tests. Without encapsulation in air, the CHNHPbI perovskite solar cells maintained 80% of photoenergy conversion efficiency from the initial value up to 100 h under light irradiation (AM 1.5, 100 mW cm). Considering the color variation of the CHNHPbI perovskite layer, the significant improvement of light stability is due to the moisture-blocking effect of the porous carbon back electrodes. The strong interaction between carbon and CHNHPbI perovskite was proposed by the measurements of X-ray photoelectron spectroscopy and X-ray diffraction of the porous carbon-perovskite layers.

The Inside Cover picture shows the best durability data of perovskite solar cells at 100 °C with cartoons of a hot perovskite solar cell waking under the hot sun, and photographs of a hot oven and hot scientists. More details can be found in the Full Paper by Baranwal et al. on page 2604 in Issue 18, 2016 (DOI: 10.1002/cssc.201600933).

No abstract