Perovskite solar cell stability and performance improved by optimizing buffer layers

Perovskite solar cells have made great strides in improving their efficiency in recent years, but they remain prone to degradation. To improve their stability, Pravakar Rajbhandari and Tara Dhakal studied the effects of having different oxide buffer layers on the performance of a perovskite solar cell.

“Perovskites are ideal top cells for tandem solar cell devices, as their bandgap is tunable in a wide range of energies,” said Dhakal.

The buffer layer plays a number of important roles in perovskite solar cells. It not only aids in efficiently extracting energy carriers, but it also provides protection against different types of damage.

Rajbhandari and Dhakal grew the buffer layers by atomic layer deposition, systematically varying the process parameters to optimize the technique. Once these were grown, the solar cells were fabricated with the buffer layer placed in between silver back electrode and an electron transport layer, and the stability and performance of each cell was tested.

Among the three oxides they studied – zinc oxide (ZnO), titanium dioxide (TiO₂) and aluminum oxide (Al₂O₃) – Rajbhandari and Dhakal found the optimal buffer layer configuration was a bilayer of ZnO and Al₂O_3. They think that this is due to ZnO’s semiconducting properties, combined with the ability of Al₂O₃ to block holes toward the cathode, which ensure charges are collected by the proper electrode. Al₂O₃ also provides an additional advantage of protecting the perovskite film from moisture.

The authors plan to continue these studies with the goal of achieving stable and efficient perovskite solar cells with a lifetime of at least 20 years. One potential route toward achieving this is by pushing the limits of the buffer layer’s thickness.

Source: “Low temperature ALD growth optimization of ZnO, TiO₂ and Al₂O₃ to be used as a buffer layer in perovskite solar cells,” by Pravakar P. Rajbhandari and Tara P. Dhakal, Journal of Vacuum Science & Technology A (2020). The article can be accessed at https://doi.org/10.1116/1.5139247 .