MONITORING THE STABILITY OF PEROVSKITE SOLAR CELLS EMPLOYING A Cu2ZnSnS4-BASED HOLE-TRANSPORTING LAYER

One of the major barriers to perovskite solar cells (PSCs) commercialization is their poor environmental stability. To overcome this problem, various strategies were investigated over years [1]. To date, one of the most attractive way is to employ inorganic carriers transporting materials due to their superior stability, facile synthesis, and low costs compared to the commercial organic one. In this scenario, kesterite Cu2ZnSnS4 (CZTS) turns out to be a promising inorganic hole transporting material (HTM) thanks to its high hole mobility (∼35 cm2 V−1 s−1 )[2]. In addition, this p-type material is composed of non-toxic abundant elements and it can be deposited by simple solution methods based on the deposition of nanoparticle (NP) inks [3]. This work aims to investigate CZTS NPs as HTM in inverted PSCs, paying particular attention to the stability of photovoltaic performance over time. The CZTS NPs ink was deposited by spin coating in air atmosphere, as all the other layers of the devices. A control device with the commercial MeO-2PACz as HTM was employed for comparison. As perovskite, it was used the methylammonium lead iodide (MAPI). X-ray photoemission spectroscopy was employed to monitor the stability of the chemical composition of the CZTS layer surface annealed at different temperatures. Photoluminescence and time-resolved photoluminescence spectroscopy were used to investigate the charge extraction and the photoluminescence quenching over time for the HTM/MAPI interface. The performance variation of devices were monitored over several weeks through solar simulator and external quantum efficiency measurements. Solar simulator was also employed to monitor the effect of moisture on devices over time. The enhanced stability of the CZTS NPs based devices with respect to MeO-2PACz based devices was demonstrated. Analysis of the photoluminescence spectra reveal no modification of the charge injection at the CZTS NPs/MAPI interface over time and the efficiency of CZTS NPs based p-i-n solar cell increased by 34% after three weeks, while for the MeO-2PACz based device it decreased by 16% over the same period. Devices with the inorganic HTM showed also a drop in efficiency of 80% after four days under moisture conditions. While the efficiency of the organic HTM based devices, under moisture conditions, dropped of 80% after two days.