Boosting perovskite cell efficiency through lattice strain
How can we push the efficiency of perovskite solar cells even closer to that of crystalline silicon? One promising approach involves adding a touch of rubidium, a metal known for its high electrical conductivity, to the original material mix.
Recent findings show that when used as an additive, rubidium can drastically reduce non-radiative recombination in certain perovskites, leading to better performance. The downside? Rubidium tends to react with other elements, forming unwanted crystalline phases that undermine its benefits.
A new study from the École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland offers a solution. Led by Lukas Pfeifer and Likai Zheng from Michael Grätzel’s research group, the team found a way to keep rubidium locked in place.
understanding wide bandgap perovskites
Perovskite solar cells, especially in tandem configurations with other technologies, rely on wide bandgap (WBG) materials. These are semiconductors that absorb high-energy photons while allowing lower-energy photons to pass through.
The problem is that under continuous illumination, WBG perovskites undergo severe phase segregation. That means the different elements in the material start to separate, creating chemically distinct regions. These regions act as traps for electrons and holes generated by incoming light.
The result? Charge carriers recombine and release energy as heat through non-radiative processes. This leads to a drop in open-circuit voltage and overall conversion efficiency.
Rubidium, when added to WBG perovskites as a tuning agent, has proven effective in suppressing non-radiative recombination. But as mentioned earlier, it can also form unwanted secondary phases that behave like structural defects, limiting its ability to stabilize the material.
how lattice strain improves perovskite cell efficiency
The EPFL team tackled this by introducing lattice strain – a controlled distortion of the atomic structure. This approach locks rubidium atoms within the perovskite lattice, preventing the formation of harmful secondary phases.
The result? The new rubidium-stabilized perovskite composition achieved an open-circuit voltage of 1.30 V – a remarkable 93.5% of its theoretical maximum. “This represents one of the lowest energy losses ever recorded in WBG perovskites,” EPFL stated.
Moreover, the modified material demonstrated a photoluminescence quantum yield above 14%, meaning it converts sunlight into electricity more efficiently.
The research was published in Science.