Date Published: February 22, 2018
Publisher: John Wiley and Sons Inc.
Author(s): Qingxia Fu, Xianglan Tang, Bin Huang, Ting Hu, Licheng Tan, Lie Chen, Yiwang Chen.
As rapid progress has been achieved in emerging thin film solar cell technology, organic–inorganic hybrid perovskite solar cells (PVSCs) have aroused many concerns with several desired properties for photovoltaic applications, including large absorption coefficients, excellent carrier mobility, long charge carrier diffusion lengths, low‐cost, and unbelievable progress. Power conversion efficiencies increased from 3.8% in 2009 up to the current world record of 22.1%. However, poor long‐term stability of PVSCs limits the future commercial application. Here, the degradation mechanisms for unstable perovskite materials and their corresponding solar cells are discussed. The strategies for enhancing the stability of perovskite materials and PVSCs are also summarized. This review is expected to provide helpful insights for further enhancing the stability of perovskite materials and PVSCs in this exciting field.
With the problem of the prospective reserves of fossil fuels and the environmental pollution caused by the consumption process, the fossil energy cannot meet the needs of sustainable development in the future.1 Therefore, it generates a strong demand for implementation of clean and renewable energy. Solar energy is an inexhaustible green energy source which provides over 1000 times of power that the entire planet requires, while photovoltaic (PV) technology provides an ideal and clean route to be pursued. However, high cost and poor flexibility of silicon solar cells limit their future development.2 Furthermore, low‐cost, environment‐friendly new solar cells become the focus of widespread concern. Among all the PV technologies, the perovskite solar cells (PVSCs) have attracted much attention3, 4, 5, 6, 7, 8, 9, 10, 11 and considered to be a major discovery in the field of photovoltaics.12 The current highest certified power conversion efficiency (PCE) of PVSCs has reached 22.1%.13
The crystal structure of perovskites originated from the calcium titanium oxide mineral (CaTiO3). The general formula for the organic–inorganic halide perovskites is 3D ABX3, where A is CH3NH+ (MA+) or NH = CHNH+ (FA), Cs+, B is a metal ion (e.g., Pb2, Sn2+), X can be I−, Br−, or Cl−.23 In an ideal cubic‐symmetry structure, the B and X ions form BX64− octahedral, and A cation is located in the cavity between four BX64− octahedra and X is surrounded by 12 nearest neighbors (Figure 1). Rapid decomposition of PVSCs was found when exposed to prolonged humidity, heat, light, oxygen, etc.6, 24, 25 One of the major influence factors of degradation is the moisture. Therefore, the preparation of PVSCs should be in a humidity relatively low level of <1% atmosphere.6 Niu and co‐workers have presented a series of chemical reactions considered responsible for the degradation of CH3NH3PbI3 in moisture in the following Equations (1)–(4), 26(1)CH3NH3PbI3 (s) ⇄ PbI2 (s) + CH3NH3I (aq.)(2)CH3NH3I (aq.) ⇄ CH3NH2+ + HI (aq.)(3)4HI (aq.) + O2 ⇄ I2(s) + 2H2O(4)2HI (aq.) ⇄ H2 + I2(s) A stable perovskite layer with high quality is crucial for the long‐term stability of PVSCs. This is because perovskite layer is very sensitive to external environment, consequently leading to the degradation of the PVSCs. In general, the stability of the perovskite layer depends on its chemical components, crystal structure, and the film quality of perovskites. Although the PCE exceeding 22% has been achieved in PVSCs with the unprecedented rapid development, commercialization of PVSCs will require the synergistic development of high‐efficiency, large‐area with long‐term stability as a competitive technology. However, the actual long‐term stability of PVSCs still lags behind their outstanding efficiency. Thus, the various causes of devices degradation need to be further explored in‐depth to achieve high performance and stable PVSCs. The stability of perovskite layer is usually optimized by compositional engineering of halides and cations, the application of 2D materials and additives. On the other hand, incorporating proper charge transport layers and electrodes or interfacial resistant agents into PVSCs is also considered as effective ways to maintain device stability as well as the efficiency of PVSCs. The authors declare no conflict of interest. Source: http://doi.org/10.1002/advs.201700387