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Electron transport layer (ETL)‐free perovskite solar cells (PSCs) have witnessed great progress via material and interface engineering. Enlighten by the wisdom from an old story of efficient silicon solar cells design, highly efficient MINP (metal/insulator/n‐type perovskite/p‐type spiro‐MeOTAD) PSC with polar insulating inter‐layer (PIIL) modified fluorine‐doped tin oxide (FTO) is reported as electron selective contact. The PIIL forms metal‐insulator‐semiconductor (MIS) junction with FTO and perovskite layer, while the n‐type perovskite forms P‐N junction with p‐type spiro‐MeOTAD. Unlike the classic MINP silicon solar cells where the I‐layer is usually neutral tunneling layer, the PIIL here optimizes the energy level alignment at the FTO/perovskite interface with its intrinsic electronic polarity while acting as an effective tunneling layer. Also, the functional group of the PIIL passivates the FTO/perovskite interface defects thus suppressing carrier recombination thereof and enhancing all device performance parameters simultaneously. Accordingly, the power conversion efficiency is greatly improved from 12.82% to 19.75%. With the enhanced electron collection and decreased carrier recombination of the MIS junction, this collaborative effect of interface engineering and defect passivation contribute to more stable ETL‐free PSC with less hysteresis. This work highlights the potential of novel device and interface design for simple‐structured, efficient and cost‐effective PSCs. [ABSTRACT FROM AUTHOR]

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]

A facile and low‐temperature solution processed UV/ozone process has been proposed for fabricating TiO2 layer, making it possible to fabricate planar perovskite solar cells at low temperature. UV/ozone photo‐annealing treatment could easily eliminate the organic components, resulting in high quality amorphous TiO2 films with high transparency, electrical conductivity, and hydrophilicity. In addition, perovskite solar cells with the UV/ozone‐treated TiO2 electron transport layer exhibiting the best power conversion efficiency of 11.58% for rigid substrate and 7.33% for flexible substrate, respectively. The results clearly indicate that UV/ozone photo‐annealing treatment is a simple and effective process of fabricating high performance flexible perovskite solar cells. Fully low‐temperature solution‐processed perovskite solar cells (PSCs) are fabricated using UV/ozone (UV/O3) treated TiO2 film as an electron transport layer. UV/O3 treatment increases the electrical conductivity and wettability of the TiO2 film, and therefore improves the performance of PSCs. By optimizing the processing time of UV/O3 treatment, the power conversion efficiency of the best rigid and flexible device is 11.58% and 7.33%, respectively. [ABSTRACT FROM AUTHOR]