Defects in perovskite films and the suboptimal interface contact largely limit the performance and stability of inverted perovskite solar cells (PSCs). A simple surface post‐treatment with N‐benzyloxycarbonyl‐d‐valine (NBDV) is developed to overcome these problems. The device performance following NBDV treatment is systemically investigated. It is showed that NBDV surface post‐treatment results in the bulk restructure of the entire perovskite film and improves the film‐forming property of [6,6]‐phenyl‐C61‐butyric acid methyl ester. The grain sizes, crystallinity, trap states, cathode interfaces, as well as the built‐in field are also improved, which result in PSC performance and stability enhancement. A relatively higher power conversion efficiency (PCE) of 21.80% is reached, which is comparable to the PCE record based on single‐crystal MAPbI3. Meanwhile, the PCE of the NBDV devices can retain ≈77% and 84% of the initial value after storage for 768 h (32 days) in air and 8376 h (349 days) in N2, respectively, while the control devices only maintain ≈53% and 38% of their initial PCE values under the same exposure conditions. This work provides means to promote bulk, surface, and interface regulation toward high performance and stable inverted PSCs.

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Efficient modification of the interface between metal cathode and electron transport layer are critical for achieving high performance and stability of the inverted perovskite solar cells (PSCs). Herein, a new alcohol-soluble rhodamine-functionalized dodecahydro-closo-dodecaborate derivate, RBH, is developed and applied as an efficient cathode interlayer to overcome the (6,6)-phenyl-C 61 butyrie acid methyl ester (PCBM)/Ag interface issues. By introducing RBH cathode interlayer, the functions of the interface traps passivation, interfacial hydrophobicity enhancement, interface contact improvement as well as built-in potential enhancement are realized at the same time and thus correspondingly improve the device performance and stability. Consequently, a power conversion efficiency (PCE) of 21.08% and high fill factor of 83.37% are achieved, which is one of the highest values based on solution-processed MAPbI 3 /PCBM heterojunction PSCs. Moreover, RBH can act as a shielding layer to slow down moisture erosion and self-corrosion. The PCE of the RBH devices still maintain 84% for 456 h (85 °C @ N 2 ), 87% for 360 h (23 °C @ relative humidity (RH) 35%) of its initial PCE value, while the control device can only maintain ≈23%, 58% of its initial PCE value under the same exposure conditions, respectively.

(2 of 15)through grain boundaries (GBs) and penetrate the charge transport layer and thus corrode the metal electrode. [12] Especially, halide ion migration-induced electrode corrosion in inverted PSCs is more serious because the aggregation and poor filmforming performance of the PCBM lead to the lack of barrier effect of the thin films on ion migration. [13] Furthermore, the metal typically evaporated at high temperatures, which may damage the organic fullerene and thus form interfacial defects. [14] The above issues could result in adverse exciton dissociation at the cathode interface. [15] Thus, overcoming the interface issues and simultaneously improving the performance and stability is urgently necessary for the development of inverted PSCs. Interface modification strategies are a promising way to overcome interface issues. Many materials have been introduced to inverted PSCs to enhance the interface energy matching, anti-corrosion as well as surface hydrophobicity, such as metal oxide (Al 2 O 3 , [16] TiO 2 , [17] ZnO [18] ) bismuth layer, [19] organometallic carbon long derivative, [20] some organic materials (polyethylenimine ethoxylated [PEIE], [21] poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt2,7-(9,9-dioctylfluorene)], [22] Bathocuproine [BCP], [3b] Rhodamine [23] ) [24] and some salts (LiF [25] ). Looking at the existing interface materials in inverted PSCs, there are still challenges in using the same material to achieve multiple interface functions to enhance the performance and stability of the devices, such as the improvement of corrosion resistance of the electrode has a negative impact on the efficient charge transfer of the cathode interface, [11,26] so it is necessary to balance the anti-corrosion performance and the performance of the device. In addition, the disadvantage of harsh preparation conditions and hygroscopic properties of them will increase the cost of the preparation and threaten the device stability.Up to now, the most promising way to overcome the above problem based on an inverted device structure is using evaporated BCP inserting between perovskite/fullerene heterojunction and metal cathodes. [27] That strategy pushes the performance of inverted devices to a high of 25%, which is comparable with that of regular n-i-p devices. [27] The excellent performance of the evaporated BCP cathode interface is ascribed to the high quality of the evaporated film and the suitable electrical property of BCP. [28] The extremely dense and uniform film can form high-quality interface contact and could act as a physical barrier layer to prevent the ions migration, which enhances the performance and stability of the devices. [28] Although the performance of the inverted PSCs has been dramatically enhanced by evaporated BCP electron transport layer, the cathode interface layer prepared by the solution method is desired by the industry at the time of promoting the industrialization of PSCs. [29] Unfortunately, the solution-processed BCP shows poor film formation because of its eas...

Energy loss and unstable properties of the interface and grain boundaries (GBs) in perovskite solar cells (PSCs) greatly limit the efficiency and stability of PSCs. Here, a polyvinyl pyrrolidone (PVP) treatment is proposed to overcome these challenges. The impact of PVP treatment on perovskite films and the corresponding performance of the devices are systemically investigated. The crystallinity, GBs, and PbI2 residues of the perovskite films are all improved via the interaction of PVP and perovskite crystals, which results in an increased grain size and enhanced built-in electric field in the devices. The trap density is dramatically decreased from 8.74 × 1015 to 4.37 × 1015 cm–3, and the additional interface electrical field of 1.26 × 106 V/cm is formed at the perovskite/PCBM interface, which dramatically eliminates the energy loss of the bulk and interface of inverted PSCs. Based on this strategy, a high power conversion efficiency (PCE) of 20.77% is achieved based on the MAPbI3/PCBM planar heterojunction. In addition, the stability of PSCs is also dramatically improved, and the PCE of PVP devices can retain 80% of its initial value after 14 days in air and can retain 99% of its initial value after 64 days in N2, while the control devices can only retain 44 and 85% of their initial PCE values under the same exposure conditions, respectively.