An international group of researchers, led by the Chungbuk National University in South Korea, has reported a tin halide perovskite (Sn-HP) solar cell that uses an additive known as 4-Phenylthiosemicarbazide (4PTSC) to reduce imperfections in the perovskite layer.
Using wide bandgap tin halide perovskites (Sn-HP) could pose an eco-friendly option for multi-junction Sn-HP photovoltaics, but rapid crystallization often results in poor film morphology and substantial defect states, hampering device efficiency. The team's work aims to introduce a novel multifunctional additive to tackle these issues.
According to the team, 4PTSC enhances solution stability and delays perovskite crystallization through Lewis acid-base adduct formation, yielding defect-free films with preferential crystal growth. The scientists explained that they chose a multifunctional molecule that acts as both a coordination complex and a reducing agent, passivates defect formation, and improves stability.
The 4PTSC additive is reportedly able to curb the insurgence of defect states through chemical interactions with uncoordinated Sn ions. This, in turn, is said to halt Sn oxidation and reduce non-radiative recombination, thus also enhancing carrier lifetime and extraction.
The team designed the cell with an indium tin oxide (ITO) substrate, a hole transport layer made of PEDOT:PSS, the perovskite absorber, an electron acceptor made of phenyl-C61-butyric acid methyl ester (PCBM), a bathocuproine (BCP) buffer layer, and a silver (Ag) metal contact.
Tested under standard illumination conditions, the cell achieved a maximum power conversion efficiency of 12.22% and a certified efficiency of 11.70%.
According to the team, the additive managed to boost the open-circuit voltage to 0.94V and realize a high efficiency for the champion device, low open-circuit voltage loss, and negligible hysteresis in the wide-bandgap Sn perovskite solar cell. Additionally, 4PTSC-1.0 devices showed exceptional stability over 1,200 hours in ambient without encapsulation. Chemical coordination between 4PTSC and SnI2 shields the perovskite surface, and passivates uncoordinated Sn2+ and halide ions, suppressing deep trap state formation.
