High Efficiency and Stable Low-dimensional Perovskite Solar Cell


Student thesis: Doctoral Thesis

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Award date21 Jun 2019


Three-dimensional (3D) organolead halide perovskites, as new promising solar energy conversion materials, have drawn much attentions due to their high efficiency and simple solution processability. Despite their enormous potential, instability of 3D perovskite to humidity, high temperature and light is still a major challenge to their device applications. Therefore, exploring high efficiency and stable perovskite is the core challenge in the perovskite photovoltaic field.

First, a facile strategy that can stabilize two-dimensional (2D) organolead halide perovskite nanocrystals (PNCs) in aqueous solutions is achieved. It is found that 2D PEA2PbI4 PNCs can be stabilized in their corresponding organic cation aqueous solutions by controlling the desorption and absorption processes of the organic cations. More importantly, reversible degradation (desorption of alkylammonium cation) and reassembly (absorption of alkylammonium cation) are confirmed. In practice, the PNCs are demonstrated as a probe for detecting Cu2+ ions in aqueous solution with high sensitivity.

Second, effects of high temperature on 2D perovskite solar cells are studied. It is found that performances of degraded 2D perovskite solar cells can be considerably improved (e. g. power conversion efficiency shows ~ 10% increase over the fresh device) by a short duration heat treatment (85ºC, 3 mins). Capacitance-frequency, X-ray diffraction and ionic diffusion calculation results suggest that heat treatment can enhance crystallinity of the degraded low dimensional perovskite and minimize the detrimental effects caused by the water molecules, leading to improved performances.

Third, two strategies are provided to improve the performance of 2D perovskite solar cells by enhancing carrier transport and inhibited low-n phases. To enhance carrier transport, 2D perovskites with reduced interlayer distance were prepared with small propane-1,3-diammonium (PDA) cations. As shown by optical characterizations, quantum confinement is no longer dominating in the PDA-based 2D perovskites, which leads to considerable enhancement of carrier transport. The improved electric properties of the interlayer-engineered 2D perovskites yield a power conversion efficiency (PCE) of 13.0%. Furthermore, environmental stabilities of the PDA-based 2D perovskites are improved due to the enhanced interaction between interlayers. We also developed a simple method to suppress the formation of low-n phases by using dimethylsulfoxide (DMSO) as a co-solvent. The 2D perovskites with alternating cations in the interlayer space (ACI) exhibit enhanced carrier lifetime and charge transport by suppressing the low-n phases. The optimized 2D ACI-based perovskite solar cell shows a PCE of 12.8%, which is also the highest efficiency among all reported ACI-based perovskite solar cells.

Fourth, a new low-dimensional hybrid perovskite based on 1D 1,4-Benzene diammonium lead iodide (BDAPbI4) perovskite is reported. Counterintuitive to the general belief that 1D perovskites are not suitable for photovoltaic devices due to the large binding energies, a high efficiency of up to 14% was achieved for solar cells based on the low-dimensional hybrid perovskites containing 1D BDAPbI4 and 3D MAPbI3. More importantly, these solar cells can retain over 95% of their efficiency upon storage for over 1,000 h and show impressive stability under continuous illumination and heating. These results give direct experimental evidence that 1D perovskites are promising photovoltaic materials with high efficiency and enhanced stabilities.