Perovskite hetero-bilayer for efficient charge-transport-layer-free solar cells

Perovskite solar cells (PSCs) have emerged as the most promising photovoltaics because of the solution processability of the ambipolar perovskite absorber, although the adjacent transporting layers (TLs) generally bring about severe cost and processing consumptions. In this work, we propose an ultrathick solution-processed FAPbI3 (FA: formamidinium)/MAPbI3 (MA: methylammonium) bilayer for efficient solar cells without TLs, which only consists of two perovskites sandwiched between two electrodes. The developed room-temperature dynamic dropping technique enables fast crystallization of MAPbI3 onto the as-fabricated FAPbI3 without harmful redissolution and unlocks the limitation of film thickness via repeatedly dropping. By carefully controlling the thickness, buried alignment, and self-doping of two perovskites, superior semiconductor qualities and sufficient light capture of the perovskite hetero-bilayer promote the resultant TL-free PSC to a record efficiency of 16.57%. Our pioneer efforts take advantage of hetero-bilayer merits in constructing efficient all-perovskite TL-free PSCs for easily processed and cost-effective commercial requirements.