Scalable technique enhances 2D layer formation in solar cells

Solar cells based on perovskites, a class of materials with advantageous optoelectronic properties, have recently achieved power conversion efficiencies (PCEs) comparable to those of some silicon-based photovoltaics. Moreover, perovskite-based solar cells could be more affordable than their silicon counterparts, which could facilitate their widespread adoption.

Despite their potential, these solar cells tend to be more sensitive to environmental factors like heat, dust, moisture and UV radiation. This means that they are less stable and degrade faster, adversely impacting their PCEs and overall performance.

One proposed strategy to boost the stability, PCEs and reliability of perovskite solar cells entails the passivation of 3D perovskite light-harvesting layers with 2D perovskites. These 2D layers can protect the light-harvesting layers, reducing their reactivity to environmental factors and thus preventing them from degrading quickly over time.

Researchers at Wuhan University of Technology and other institutes worldwide recently devised a strategy to prompt the formation of homogenous 2D perovskite passivation layers in perovskite-based solar cells. Using their proposed method, outlined in a paper published in Nature Energy, they were able to achieve good active-area efficiencies and stabilities in perovskite solar modules based on formamidinium and cesium.

"The formation of a homogeneous passivation layer based on phase-pure two-dimensional (2D) perovskites is a challenge for perovskite solar cells, especially when upscaling the devices to modules," wrote Jing Li, Chengkai Jin and their colleagues in their paper.

"We reveal a chain-length-dependent and halide-related phase separation problem of 2D perovskite growing on top of three-dimensional perovskites. We demonstrate that a homogeneous 2D perovskite passivation layer can be formed upon treatment of the perovskite layer with formamidinium bromide in long-chain ( >10) alkylamine ligand salts."

The researchers found that the homogenous 2D passivation layer formed using their proposed strategy produced a uniform, stable and high-quality 3D/2D heterostructure perovskite. This boosted both the efficiency and stability of the resulting perovskite solar cells, which varied slightly based on their size.

"We achieve champion active-area efficiencies of 25.61%, 24.62% and 23.60% for antisolvent-free processed small- (0.14 cm²) and large-size (1.04 cm²) devices and mini-modules (13.44 cm²), respectively," wrote Li, Jin and their colleagues.

"This passivation strategy is compatible with printing technology, enabling champion aperture-area efficiencies of 18.90% and 17.59% for fully slot-die printed large solar modules with areas of 310 cm² and 802 cm², respectively, demonstrating the feasibility of the upscaling manufacturing."

Notably, the team found that the formation of the 2D perovskite passivation layer also boosted the stability of solar cells. Mini-modules exhibited a remarkable operational stability, with a T₈₀ lifetime exceeding 2,000 h at maximum power point tracking (MPPT) under continuous light illumination.

The strategy proposed by the researchers is also scalable and could be easy to implement on a large scale using existing printing technologies. In the future, it could help to accelerate the commercialization of more affordable solar modules based on perovskites.