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Efficient electron transport layer–free perovskite solar cells (ETL‐free PSCs) with cost‐effective and simplified design can greatly promote the large area flexible application of PSCs. However, the absence of ETL usually leads to the mismatched indium tin oxide (ITO)/perovskite interface energy levels, which limits charge transfer and collection, and results in severe energy loss and poor device performance. To address this, a polar nonconjugated small‐molecule modifier is introduced to lower the work function of ITO and optimize interface energy level alignment by virtue of an inherent dipole, as verified by photoemission spectroscopy and Kelvin probe force microscopy measurements. The resultant barrier‐free ITO/perovskite contact favors efficient charge transfer and suppresses nonradiative recombination, endowing the device with enhanced open circuit voltage, short circuit current density, and fill factor, simultaneously. Accordingly, power conversion efficiency increases greatly from 12.81% to a record breaking 20.55%, comparable to state‐of‐the‐art PSCs with a sophisticated ETL. Also, the stability is enhanced with decreased hysteresis effect due to interface defect passivation and inhibited interface charge accumulation. This work facilitates the further development of highly efficient, flexible, and recyclable ETL‐free PSCs with simplified design and low cost by interface electronic structure engineering through facile electrode modification. [ABSTRACT FROM AUTHOR]

Interfacial engineering plays an important role to improve the photovoltaic performance of organic solar cells (OSCs). Herein, CdSe/ZnS quantum dots (QDs) are used as a cathode interlayer (CIL) modifier. By using this strategy, an enhanced power conversion efficiency (PCE) from 13.0% to 14.6% is achieved, mainly due to the increase in open‐circuit voltage (Voc) and short‐circuit current density (Jsc). A single QD layer of a proper size can reduce the defects on the surface of the active layer and smoothen the interface between the active layer and cathode. Furthermore, the low work function of the QDs with dipole moment facilitates charge transport and suppresses charge recombination at the interface by strengthening the built‐in field, thus contributing to the enhancement of PCE. The excitons generated by the QDs can also be dissociated at the IT‐4F/QD interface, which boosts the photon harvesting capability of the device. As a result, a high PCE of 14.6% is achieved for QD‐modified OSCs. [ABSTRACT FROM AUTHOR]