Researchers from NingboTech University, Hunan Institute of Engineering, Hangna Nanofabrication Equipment Co. and University Malaysia Sabah have developed an inverted perovskite solar cell with an interface passivator based on lead carbanion (Pb–C–), that reportedly achieved the highest open-circuit voltage ever recorded for an inverted perovskite PV device. The lead carbanion layer was responsible for reducing defects at the interface between the perovskite layer and the electron transport layer.
Inverted perovskite cells, or “p-i-n” cells, have the hole-selective contact p at the bottom of intrinsic perovskite layer i with electron transport layer n at the top. Conventional halide perovskite cells have the same structure but reversed – a “n-i-p” layout. In a n-i-p architecture, the solar cell is illuminated through the electron-transport layer (ETL) side; in the p-i-n structure, it is illuminated through the hole‐transport layer (HTL) surface. Inverted perovskite solar cells are known for their impressive stability but have been held back by relatively low efficiencies. This issue mainly arises at the point where the perovskite layer meets the electron transport layer, causing energy loss instead of being converted into useful power, primarily caused by carrier recombination, especially at the interface between perovskite and the electron transport layer.
The team explained that lead carbanion complexes are among the least explored and understood carbon complex species and, so far, have only been observed in the liquid phase. In their recent work, the researchers reported the synthesis of bulk lead carbanion complexes and set out to explore their influence on the photoelectric properties of perovskite solar cells.
The scientists explained that, with the carbanion treatment, the residual lead cation (Pb2+) at the interface could be neutralized and fully coordinated. They performed a comprehensive investigation of perovskite films properties, using photoluminescence (PL) mapping and scanning electron microscope (SEM) images, and found that carbanion passivation reduces defect-rich domains and decreases grain isolation on the perovskite surface.
The group fabricated the solar cell with a substrate made of indium tin oxide (ITO), self–assembled monolayers (SAM) as an HTL, the perovskite absorber, the Pb–C– passivator, an ETL based on phenyl-C61-butyric acid methyl ester (PCBM), a bathocuproine (BCP) buffer layer, and a silver (Ag) metal contact.
Tested under standard illumination conditions, the device reportedly showed an efficiency of up to 25.16%, an open-circuit voltage of 1.17 V, a short-circuit current density of 25.30 mA/cm2 and a fill factor of 85.0%.
The performance was primarily attributable, according to the scientists, to a high open-circuit voltage of 1.17 V and a minimal voltage loss of 0.38 V. The team was said to achieve the highest open-circuit voltage ever recorded for an inverted perovskite PV device.
Looking ahead, the research group is planning to investigate other lead carbanion complexes with different cations, which are expected to synthesize more crystals, and should find applications beyond solar photovoltaics.
