Researchers show that target therapy for buried interface can help create stable and efficient perovskite solar cells

Researchers from China's University of Science and Technology (SUSTech), Chinese Academy of Sciences (CAS), City University of Hong Kong (CityU) and Korea University have developed an effective strategy to modify the Tin dioxide (SnO₂)/perovskite buried interface by passivating the buried defects in perovskite and modulating carrier dynamics via incorporating formamidine oxalate (FOA) in SnO₂ nanoparticles.

Tin dioxide (SnO₂) is a commonly used electron transport material for n-i-p-type perovskite solar cells (PSCs) due to its high light transmittance and electron mobility, suitable energy levels, good stability under UV irradiation, and it can be processed at low temperatures. The buried interface of perovskite/SnO₂ plays a major role in achieving high efficiency and stability. However, the non-exposed buried interface is challenging to study and manipulate.

The team of researchers has reported their newly developed strategy for precisely modulating the buried interface through incorporating formamidine oxalate (FOA) in a colloidal SnO₂ -based electron-transporting layer. They found that both formamidinium (FA⁺) and oxalate ions showed longitudinal gradient distribution in the SnO₂ layer, and mostly accumulated at the SnO₂/perovskite buried interface. The modified SnO₂ exhibited higher Fermi level, which induces better energy level alignment between perovskite and SnO₂ -FOA, and helps avoid carrier accumulation at the interface and improves open-circuit voltage.

Moreover, the FOA could modulate crystal growth of upper perovskite films, which enables high-quality perovskite films with minimized grain boundaries and superior interface contacts.

FA⁺ cations and oxalate anions could suppress oxygen vacancies and tin interstitial defects on the SnO₂ surface and FA⁺/Pb₂⁺ associated defects at the perovskite buried interface contemporaneously, which contribute to achieve target defect passivation. Ultimately, the FOA-modified buried interface increased the record power conversion efficiency to 25.05% with enhanced stability of corresponding devices under light, heat, and moisture conditions.