Surface modification of electron transport layer for high efficiency printable perovskite photovoltaics

Abstract

Perovskite solar cells have emerged as an attractive form of renewable energy in recent times. There have been many studies on perovskite solar cells and the performance of such devices that risen considerably. It is also versatile as there are many architectures. Carbon perovskite solar cells which have the triple mesoscopic structure can be mass produced, solution processed and have a low cost. The electron transport layer that is commonly used is TiO2. Although it is a good electron transport layer, there still exists possibilities for improving the electrical properties of TiO¬2 for better photovoltaic performance. In this report, it was studied how the TiO2 electron transport layer of carbon perovskite cells can be modified using Cs¬2CO3 aqueous solution. Cs2CO3 was used for surface modification for better electron transport in the ETL. Through characterisation, such as SEM, it was seen that Cs2CO3 was effectively deposited on the surface of the electron transport layer. Subsequent tests included PL, UV-Vis spectroscopy and finally, device performance using Solar Simulator. It was observed that TiO2 films treated with Cs2CO3 using chemical bath deposition had lower transmittance especially in the wavelengths of 300-479nm compared to pristine TiO2. The bandgap of TiO2 was also reduced because of Cs2CO3 treatment. The perovskite film formed on TiO2 treated with Cs2CO3 displayed higher absorption in all wavelengths and higher PL quenching, compared to perovskite film on pristine TiO2. Carbon perovskite solar cells where TiO2 electron transport layer was treated with Cs2CO3 showed average PCE of 9.9%, an increase from control devices with PCE of 5.7%. Lastly, light dependence study conducted showed that devices with CS2CO3 treatment had the lowest trap assisted recombination compared to other variants