Elimination of Charge Transport Layers in High-Performance Perovskite Solar Cells by Band Bending

In this paper, band bending at an ITO–perovskite interface was proposed to fabricate highly efficient perovskite solar cells without electron or hole transport layers. Direct deposition of a perovskite (MAPbI3-xClx) on clean ITO results in downward shift of the band of the perovskite by about 170 meV at the ITO–perovskite interface, preventing holes from recombining with electrons collected in the ITO. The device without a dedicated electron transport layer or any modifications achieves a power conversion efficiency (PCE) of 17.42%. The band bending direction changes when a Sn–Pb mixed narrow band gap (1.21 eV) perovskite ((FASnI3)0.6(MAPbI3)0.4) is used to replace MAPbI3-xClx. An upward band shift of about 110 meV was observed at the ITO–perovskite interface, facilitating hole extraction while blocking electron transfer from the perovskite to ITO. Perovskite solar cells made from this narrow band gap Sn–Pb mixed perovskite achieves a PCE of 18.31%, the highest one without a hole transport layer among those in the known literature studies. Thus, band bending is proved to be an effective way to eliminate charge transport layers in perovskite solar cells.