期刊
ACS ENERGY LETTERS
卷 2, 期 3, 页码 709-715出版社
AMER CHEMICAL SOC
DOI: 10.1021/acsenergylett.6b00727
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资金
- Solar Photochemistry Program of the U.S. Department of Energy
- Office of Science
- Office of Basic Energy Sciences
- Division of Chemical
- Geological and Biosciences [DE-ACO205CH11231]
- Laboratory Directed Research and Development Program of Lawrence Berkeley National Laboratory under U.S. Department of Energy [DE-ACO2-0SCH11231]
- Electronic Materials program - Director, Office of Science
- Materials Sciences and Engineering Division of the U.S. Department of Energy [DE-ACO2-05CH11231]
- Office of Basic Energy Sciences of the U.S. Department of Energy [DESC0012363]
- Oregon BEST
- Swiss National Science Foundation [P2EZP2_155586]
- Swiss National Science Foundation (SNF) [P2EZP2_155586] Funding Source: Swiss National Science Foundation (SNF)
Organometal halide perovskite semiconductors have emerged as promising candidates for optoelectronic applications because of the outstanding charge carrier transport properties, achieved with low-temperature synthesis. Here, we present highly sensitive sub-bandgap external quantum efficiency (EQE) measurements of Au/spiro-OMeTAD/CH3NH3Pb(I1-xBrx)(3)/TiO2/FTO/glass photovoltaic devices. The room-temperature spectra show exponential band tails with a sharp onset characterized by low Urbach energies (E-u) over the full halide composition space. The Urbach energies are 15-23 meV, lower than those for most semiconductors with similar bandgaps (especially with E-g > 1.9 eV). Intentional aging of CH3NH3Pb(I1-xBrx)(3) for up to 2300 h, reveals no change in E-w despite the appearance of the PbI2 phase due to decomposition, and confirms a high degree of crystal ordering. Moreover, sub-bandgap EQE measurements reveal an extended band of sub-bandgap electronic states that can be fit with one or two point defects for pure CH3NH3PbI3 or mixed CH3NH3Pb(I1-xBrx)(3) compositions, respectively. The study provides experimental evidence of defect states close to the midgap that could impact photocarrier recombination and energy conversion efficiency in higher bandgap CH3NH3Pb(I1-xBrx)(3) alloys. [GRAPHICS]
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