Abstract
Metal halide perovskite solar cells (PSCs) are emerging candidates in next-generation photovoltaics thanks to their extremely low fabrication cost and high power conversion efficiencies (PCEs). The lab-scale PSCs have achieved a record PCE of over 25%, exhibiting a promising future compared to other thin-film solar cells. Amongst all types of PSCs, devices with the inverted planar heterojunction structures are more beneficial for commercial applications due to their low-temperature processing, easy fabrication, and satisfactory compatibility with mass production and tandem solar cells. Encouragingly, the inverted PSCs have reached a certified PCE of 22.8% for the single junction and 29.5% for the tandem cell.
In this thesis, the single-junction inverted PSCs have been systematically investigated, consisting of device fabrication and optimisation, interface modification, and long-term stability study. Tremendous efforts are dedicated to device optimisation in order to establish reproducible protocols for the fabrication of state-of-the-art inverted PSCs. Furthermore, two types of passivating agents, including conjugated polyelectrolytes (CPEs) and organic halide salts (OHSs), are introduced to further enhance the PCEs. The results show that the CPEs can tailor the perovskite adjacent interfaces simultaneously, namely, between the hole transport layer (HTL) and the perovskite, and between the perovskite and electron transport layer (ETL), whilst the OHSs only benefit the perovskite/ETL interface. These two passivating agents are able to suppress the interface-mediated recombination losses and improve the PCEs of the resultant devices. Through the interfacial modifications, the champion devices reached a PCE of over 21% alongside a high open-circuit voltage (VOC) of 1.18 V. Finally, the stability of the inverted devices has been studied, including the short-term testing (several to hundreds of minutes) and long-term shelf-life testing (hundreds to thousands of hours). Compared to OHSs, the CPEs are favourable for device long-term stability, maintained over 80% of their initial PCEs after 800 h.