Perovskite solar cells (PSCs) have drawn unprecedented attention due to their skyrocketed power conversion, however the reported fill factors (FFs) still lag behind commercialized solar cells, and there lacks comprehensive...

Among the emerging photovoltaic technologies, rigid perovskite solar cells (PSCs) have made tremendous development owing to their exceptional power conversion efficiency (PCE) of up to 25.7%. However, the record PCE of flexible PSCs (≈22.4%) still lags far behind their rigid counterparts and their mechanical stabilities are also not satisfactory. Herein, through modifying the interface between perovskite and hole transport layer via pentylammonium acetate (PenAAc) molecule a highly efficient and stable flexible inverted PSC is reported. Through synthetic manipulation of anion and cation, it is shown that the PenA+ and Ac− have strong chemical binding with both acceptor and donor defects of surface‐terminating ends on perovskite films. The PenAAc‐modified flexible PSCs achieve a record PCE of 23.68% (0.08 cm2, certified: 23.35%) with a high open‐circuit voltage (VOC) of 1.17 V. Large‐area devices (1.0 cm2) also realized an exceptional PCE of 21.52%. Moreover, the fabricated devices show excellent stability under mechanical bending, with PCE remaining above 91% of the original PCE even after 5000 bends.

The narrow bandgap (≈1.2 eV) Pb-Sn alloyed perovskite solar cell is a promising bottom component cell for all-perovskite tandem devices that are expected to offer higher efficiency than the theoretical Shockley-Queisser limit of the single-junction solar cells. The density functional theory (DFT) study reveals that the Pb-Sn perovskite film with the (100) orientation would render significantly reduced trap density, which is a critical figure-of-merit for perovskite device performance. Alkyl diamine is therefore designed to first anchor onto the surface as a nucleation agent to modulate the Pb-Sn perovskite growth to proceed preferentially along with the (100) orientation. It is observed that the diamine cations not only effectively induced the crystal growth at the nucleation stage, but also remained on the crystal surface to eventually passivate the resultant perovskite film. As a result, the diamine-based films show (100) preferred orientation with superior optoelectronic properties, as predicted by the DFT investigation. Consequently, the champion power conversion efficiency of 20.03% is achieved, one of the highest for this type of device. These findings provide a practicable strategy to theoretically design surface nucleation to induce preferential growth of perovskite material for better optoelectronic performance.

Wide-bandgap (≥1.68 eV) inverted perovskite solar cells (PSCs) have been recognized as promising top component cells on the commercial crystalline silicon cell to surpass its Shockley-Queisser efficiency limit. However, the power conversion efficiency (PCE) is dramatically limited by the huge open-circuit voltage (V OC ) loss. Herein, we propose a proton-transfer-induced in situ defect passivation strategy to reduce the nonradiative recombination to minimize the V OC loss. Specifically, a liquid-form neutral amine, 3,4,5-trifluorobenzylamine (TFBA) was added into ethyl acetate (EA) as anti-solvent for the film preparation, which induces proton-transfer from the formamidinium (FA) and methylammonium (MA) in the perovskite precursors to the TFBA. The protonated TFBA exhibits a gradient distribution near the surface of the perovskite film, achieving in situ defect passivation. As a result, TFBA-based 1.68 eV-bandgap inverted PSCs afforded a PCE of 20.39%, one of the highest for cells with this bandgap. Meanwhile, due to the strong interaction between TFBA and the perovskite film, the mixed-halide perovskites demonstrate much better photostability. Our findings offer an effective strategy to passivate defects in PSCs.