Simultaneous bottom-up double-layer synergistic optimization by multifunctional fused-ring acceptor with electron-deficient core for stable planar perovskite solar cells with approaching 24% efficiency

The interface defects and energy barrier between perovskite and electron transport layer (ETL) severely hinder the further improvement of the efficiency and stability of the perovskite solar cells (PSCs). Therefore, there is an urgent desire to develop multifunctional interface modulators to manage the interface between perovskite and ETL. Here, a multifunctional bottom-up double-layer interface modulation strategy is developed, that is, 2,2 '-[[12,13-Bis(2-butyloctyl)- 12,13-dihydro-3,9-dinonylbisthieno[2 '',3 '':4 ',5 ']thieno[2 ',3 ':4,5]pyrrolo[3,2-e:2 ',3 '-g][2,1,3]benzothiadiazole-2,10-diyl]bis[methylidyne(5,6-chloro-3-oxo-1H-indene-2,1(3 H)-diylidene)]]bis [propanedinitrile] (BTP-eC9) is combined in the SnO2/perovskite interface to achieve high efficiency and outstanding stability of PSCs. The BTP-eC9 can effectively prevent the detrimental contact between the FTO and perovskite and construct two electron transport paths by formatting the cascade energy level structure, which can eliminate the probability of carrier recombination and improve the interfacial carrier transfer. Chemically, BTP-eC9 can not only passivate the uncoordinated Sn ions, showing high conductivity and large photo-generated carrier transmission efficiency, but also can effectively passivate the underlying perovskite defects through a spontaneous bottom-up passivation process and improve the nucleation and crystallization kinetics of perovskite films. Based on the above efficient synergy, the power conversion efficiency (PCE) of up to 23.10% was obtained and it retains 90% of its original PCE after 8000 h in the ambient atmosphere without any encapsulation by the two-step method. In addition, the champion PCE of 23.75% with ultrahigh open-circuit voltage (V-OC) of 1.25 V was achieved by the one-step method and this V-OC is the highest value of a perovskite film with a band gap of approximately 1.60 eV, demonstrating the effectiveness and universality of this strategy. This research guides design methods of the ETL to raise the PCE of PSCs by interfacial engineering.