Enhanced efficiency and reduced hysteresis by TiO2 modification in high-performance perovskite solar cells

Recent research has focused on increasing the open-circuit voltage (VOC) and current density (JSC) of perovskite solar cells (PSCs) by introducing p- or n-type dopants with higher electronegativity than Ti into the TiO2 electron transport layer (ETL). However, these kinds of dopant create undesired charge traps that hinder charge transport through TiO2. Therefore, the improvement in VOC is often accompanied by an undesired current density–voltage (J–V) hysteresis problem. Herein, we demonstrate that the introduction of 4-chlorobenzoic acid (4-ClBA-TiO2) dopant into TiO2 not only overcomes the J–V hysteresis issue but also increases the VOC, JSC and power conversion efficiency (PCE) in mesoscopic PSCs. Also, the material shown the better device performance compared to the state-of-art ETL, with the 4-CLBA-TiO2. We speculate that the interaction between the 4-ClBA and the perovskite interface is more selective for electrons. Further the 4-ClBA-TiO2 electron mobility has been improved 1.9 times compared with TiO2. As a result, for mesoscopic PSCs, the doping of 4-ClBA-TiO2 increases the efficiency from 18.23% to 20.22%, while the hysteresis is largely reduced from 20.2% to 1.5%. To the best of our knowledge, this is the first report using the spin coating blocking layer to achieve over 20%. Thus, we believe that this approach will be an effective design strategy capable of enhancing the performance of PSCs with less hysteresis.