PVK has been extensively tried in conventional OIH-PVK. Pure Sn, [10] Sn-Pb, [11,12] Sn-Cu-Pb, [13] and In-Pb [14] based alloys reduced ≥10% Pb content in OIH-PSCs. Regardless of the instability of Sn 2+ , high efficiency is achieved in Sn-Pb alloyed solar cells because of the energy state tuning and high quality perovskite film formation. Doping of Pb is also tried in CsPbX 3 based I-PVK. 10% Pb is reduced in CsPb 0.9 Sn 0.1 IBr 2 , which was applied in carbon counter electrode based I-PSCs. Other doping elements of Sr, [15] Bi, [16] Mn, [17,18] Ln 3+ , [19] and In 3+[20] were tried aiming to stabilize the phase or increase the performance. However, the doping amounts were usually below 5%, which still remains a large amount of Pb. Because of the special physicochemical property of Pb, large amount of new substitute might greatly change the energy band structure and induce trap states in the bandgap to deteriorate opto-electronic property. Therefore, seeking stable substitutes to achieve lead-less CsPbX 3 PSCs with high PCE is a great challenge.Aiming for high PCE, high quality large PVK crystals, and even single-crystal with a few GBs is pursued to reduce the defect states in OIH-PVK. [21][22][23][24][25] Moreover, the GB is modified to further passivate the defect states. [26,27] Recently, obtaining high quality I-PVK films with low defect states became a focus of attention, which largely boosts the PCE. [17,[28][29][30][31][32] However, the crystalline process of Pb-reduced I-PVK might be particularly different from the pure CsPbX 3 films because of the differed physicochemical property between the substitute ion and the Pb analog. [10][11][12] Therefore, formation of high quality Pb-reduced I-PVK films should be paid special attention to.In this work, stable and abundant Zn is used to reduce ≥10% Pb in CsPbI 2 Br. Due to the different physicochemical property of Zn 2+ , the crystal morphology and energy band structure are effectively tuned. 10% Pb reduction in CsPb 0.9 Zn 0.1 I 2 Br successfully diminishes GB trap states and slightly reduces the energy bandgap, greatly contributing to the enhanced performance of PSCs. Stable Zn 2+ and high quality CsPb 0.9 Zn 0.1 I 2 Br also benefit the device stability.To reduce the Pb content, PbI 2 is partly replaced by ZnI 2 in the starting material, and the molar ratio of Cs:(Pb+Zn):(Br+I) in the precursor is kept to be 1:1:3. The ZnI 2 doped precursors and the films are noted as CsPb 1−x Zn x I 2 Br (x is the molar percentage of Zn, x = 6%, 10%, and 12% in our work). The X-ray Fabrication of efficient Pb reduced inorganic CsPbI 2 Br perovskite solar cells (PSC) are an important part of environment-friendly perovskite technology. In this work, 10% Pb reduction in CsPb 0.9 Zn 0.1 I 2 Br promotes the efficiency of PSCs to 13.6% (AM1.5, 1sun), much higher than the 11.8% of the pure CsPbI 2 Br solar cell. Zn 2+ has stronger interaction with the anions to manipulate crystal growth, resulting in size-enlarged crystallite with enhanced growth orientation. Moreover, the grain ...

Efficient charge transport is especially important for achieving high performance of perovskite solar cells (PSCs). Here, molecularly designed graphite–nitrogen doped graphene quantum dots (GN-GQDs) act as a functional semiconductor additive in perovskite film. GN-GQDs with abundant N active sites participate in the crystallization of perovskite film and effectively passivate the grain boundary (GB) trap states by Lewis base/acid interaction. Moreover, the semiconductive GN-GQDs at GBs exhibit matched energy structure with the perovskite, which facilitate the charge transport at GBs. GN-GQDs also show n-type dopant property to upshift the Fermi energy level of perovskite films. It largely improves the charge transport in PSCs and reduces the interface recombination at the same time. Profiting from these advantages, inverted planar PSCs with NiO/perovskite/PCBM/BCP structure achieves high efficiency of 19.8% with no hysteresis phenomenon. GN-GQDs modified PSCs also show high stability even without encapsulation, benefiting from the protected GBs and more hydrophobic surface of the modified film. This work highlights a judicious design method of GQDs additive to satisfy efficient and stable PSCs.

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