Boosting Efficiency and Stability of Perovskite Solar Cells with CdS Inserted at TiO₂/Perovskite Interface

Abstract

Organic–inorganic hybrid perovskite solar cells have undergone an unprecedented development as the next‐generation photovoltaic devices in recent years. The power conversion efficiency and stability are the key factors attracting great attentions from both academic and industrial communities. Here, a nonoxide CdS layer is inserted between TiO2 and perovskite to passivate the TiO2 interface in planar‐type perovskite solar cells. After introducing the CdS layer, significantly enhanced air stability and suppressed recombination between the trapped electrons and perovskite related to inverse transport are observed. At the optimum CdS thickness, a champion power conversion efficiency of 14.26% is achieved compared with 10.31% for the reference CdS‐free devices. This impressive efficiency also surpasses that of previously reported perovskite solar cells based on CdS. The largely improved performance is ascribed to the increased Fermi level of the electron transport layer, more efficient charge transport, and lower recombination rates.

CdS as Electron Transport Layer for Low‐Hysteresis Perovskite Solar Cells

“…In contrast, when using CdS as ETL (Figure b), the PCEs are only up to 11%, but the difference between “down” and “up” PCE becomes smaller and the hysteresis factor can be close to 0 after pre‐biasing for 60 s (Figure b). As mentioned above, the electron mobility of CdS is much higher than that of TiO x , so that the electrons can be transported faster to the transparent electrode and the recombination should be reduced when using CdS as ETL.…”

“…There have been many attempts to replace TiO x by another ETL material which provides high efficiencies, but allows simple and low‐cost production. Other metal oxides like ZnO, SnO 2 , and In 2 O 3 work in principle, but they either show lower stability due to reaction with degradation products of the perovskite (e.g., ZnO reacts with HI), or they need relatively high temperatures (≥180 °C for SnO 2 or In 2 O 3 ) . Another well‐known ETL material used for organic solar cells are fullerenes, especially [6,6]‐phenyl‐C 61 ‐butyric acid methyl ester (PCBM).…”

“…A different class of n‐type solution‐processable material that is well established for classical thin film technologies are metal sulfides, in particular CdS which can easily be grown on large scales with high homogeneity. The electron mobility of CdS is with 350 cm 2 V −1 s −1 several orders of magnitude higher than that of TiO x , so that a more efficient charge transport and lower recombination rates are achieved . At the same time CdS acts as an efficient hole blocking layer, avoiding direct recombination of electrons from the contact with holes inside the perovskite layer.…”

“…Due to its advantages, a few first results on CdS as ETL for perovskite solar cells have been published recently …”

Two-dimensional organic-inorganic hybrid perovskite: from material properties to device applications

“…However, the Achilles heel of PeSCs is their stability resisting high temperature, illumination and humidity. Through ETL or HTL property improvement [82][83][84][85][86], interfaces engineering [87][88][89] and active layer modification [90], the device stability can be improved. Utilizing 2D perovskite as the photoactive layer offers a strategy for stable solar cells with simple spin-coating process.…”