Enhancing the performance of n-i-p perovskite solar cells by introducing hydroxyethylpiperazine ethane sulfonic acid for interfacial adjustment.

Although the power conversion efficiency (PCE) of perovskite solar cells (PSCs) has improved greatly in recent years, the challenges of efficiency and stability still need to be overcome before these solar cells can be used in commercial applications. Here, a weak acid buffer, hydroxyethyl piperazine ethane sulfonic acid (HEPES), is used to passivate the interface of an SnO2 electron transport layer (ETL) and a photoactive layer in n-i-p solar cells. The device efficiency based on a SnO2/HEPES ETL reaches 20.22%, which is 9.7% higher than that of the control (18.43%), and the device stability is also significantly improved. The improvement in the device performance is mainly due to the introduction of the HEPES interface layer to adjust the interface energy level, which also improves the crystallinity of the perovskite film and reduces the interface defects. Electrochemical impedance spectroscopy and transient photovoltage/photocurrent results show that the HEPES-modified PSCs have lower charge transfer resistance, weaker leakage current intensity and improved interfacial charge separation and transport.