Synergistic Interface Energy Band Alignment Optimization and Defect Passivation toward Efficient and Simple‐Structured Perovskite Solar Cell

Abstract

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.

Dopant‐Free, Amorphous–Crystalline Heterophase SnO2Electron Transport Bilayer Enables >20% Efficiency in Triple‐Cation Perovskite Solar Cells

“…Numerous research outcomes have demonstrated that the energy band alignment and interfacial charge recombination between the ETL and perovskite layer exert a significant impact on the device performance. [ 4–7 ] Therefore, it is pre‐requisite to develop an ETL with tailored morphology, optoelectronic properties, and compatible band alignment with perovskite, in order to fabricate high performance PSCs.…”

Suppressing Interfacial Charge Recombination in Electron‐Transport‐Layer‐Free Perovskite Solar Cells to Give an Efficiency Exceeding 21 %

“…Other fascinating optoelectronic properties of these magic perovskite materials, for example, ambipolar charge transport capability, low exciton dissociation energy and long charge diffusion length, point to the great potential for constructing high‐performance, ETL‐free PSCs, which is thought to be a perfect solution to address the dilemma of balancing high efficiency and low production cost [12] . Owing to continuous research efforts to optimize the materials, interfaces, device structures and fabrication processes, the power conversion efficiencies (PCEs) of state‐of‐the‐art ETL‐free PSCs already exceed 20 %, which is approaching the certified PCE as high as 25.2 % for their ETL‐containing counterpart [13–19] . The next step is to further reduce the efficiency gap between the ETL‐free “simplified” PSCs and devices with standard architecture, but this is still a great challenge.…”

Self‐Assembled Ionic Liquid for Highly Efficient Electron Transport Layer‐Free Perovskite Solar Cells

“…To simplify the device structure of PSCs, HTL‐free and ETL‐free PSC devices have come onto the horizon of researchers . The photovoltaic performance of ETL‐free PSCs can be improved by utilizing perovskite films with large‐sized perovskite crystals or adding extra PbI 2 into the perovskite precursor solution .…”