Surface engineering of mesoporous-TiO2 electron transport layer for improved performance of organic-inorganic perovskite solar cells via suppressing interface defects, enhancing charge extraction and boosting carrier transport

Organic-inorganic perovskite solar cells (PrSCs) have emerged as a promising solar photovoltaic technology in terms of realizing high power conversion efficiency (PCE). However, their limited lifetime and poor device stability limit their commercialization in future. In this regard, interface engineering of the electron transport layer (ETL) using 2D materials have been currently used owing to their high carrier mobility, high thermal stability and tunable work function which in turn enormously impact the charge carrier dynamics. In this work, we report an easy and effective way of simultaneously enhancing the efficiency and air-stability of PrSCs via interface engineering by incorporating 2D-MoS2 (bi/tri-layered) in mesoporous-titanium dioxide (mp-TiO2) scaffold electron transport buffer layer, and using CVD grown perovskite layers. The PrSCs were fabricated in ambient air conditions in device configuration, FTO/c-TiO2/mp-TiO2:2D-MoS2/CH3NH3PbI3/P3HT/Au, with an active area of 0.16 cm2. The best device using c-TiO2/mp-TiO2:2D-MoS2 (0.5 wt%) ETL exhibited a substantial increase in PCE ∼13.04% as compared to PCE ∼8.75% realized in reference device fabricated without incorporating MoS2 in mp-TiO2 buffer layer. The incorporation of MoS2 nanoflakes in mp-TiO2 ETL not only enhances the PCE to ∼49%, but also improve the lifetime (retaining PCE ∼86% of its initial value up to 500 hrs, without encapsulation). The enhancement in performance of c-TiO2/mp-TiO2:2D-MoS2 ETL based devices as compared with reference c-TiO2/mp-TiO2 ETL based devices is attributed to, (i) reduction in the work function of mp-TiO2 ETL buffer on dispersion of 2D-MoS2 nanoflakes forming of a perfect interface at ETL/perovskite offering extremely less interfacial energy barrier to promote the charge extraction process at the interface, and suppress the surface recombination losses, (ii) fast charge collection as 2D-MoS2 in TiO2 strongly support the electron transport due to their highly crystalline nature, and (iii) lifetime improvement due to better moisture stability of 2D-MoS2 and high quality of chemical vapor grown perovskite thin films. This work presents an efficient mp-TiO2:2D-MoS2 scaffold ETL for realizing high performance, low cost, air-processed PrSCs for their future development.