Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV16)
Publication date: 28th March 2016
The interest in organic-inorganic hybrid solid-state solar cells based on organolead halide perovskite has increased over the past few years following the recently reported power conversion efficiency (PCE) over 20% [1]. Recently, inorganic cesium lead halide (CsPbX3) perovskite have been reported in working solar cells, which suggests a potential for making even more stable inorganic perovskite solar cells than the hybrid organic-inorganic materials currently displaying the highest efficiencies [2-4]. For future application such as hot-carrier solar cells, the understanding of photoexcited carrier dynamics are very important.
In this study, for the first time, we studied ultrafast photoexcited carrier relaxation dynamics, especially hot carrier cooling, in perovskite CsPbI3 using a transient absorption (TA) spectroscopy. We find that three slow hot carrier cooling processes exist in CsPbI3. First, a non-equilibrium hot carrier cooling is observed within 0.8 ps. A TA bleach peak corresponding to hot carriers (“hot carrier peak”) red shifts from 2.2 eV to 2.0 eV during 0.3 ps - 0.6 ps, and another TA bleach peak corresponding to the bandgap absorption (1.8 eV) appeared (“band edge peak”) after 0.6 ps. Secondly, quasi-equilibrium hot carrier cooling is observed after 0.8 ps. After 0.8 ps, the “hot carrier peak” disappeared and the high-energy tail (1.85 eV-2 eV) of the “band edge peak” is broadened, corresponding to a quasi-thermalized carrier distribution with a higher temperature than the lattice temperature. By calculating the carrier temperature Tc for the quasi-equilibrium carrier distribution, we found that there are two principle cooling processes: hot carriers cool from 0.9 ps to 2 ps with a decay constant of 380 fs, and cool after 2 ps with a decay time constant of about 4.5 ps. More interestingly, we found an ultrafast hot holes transfer from CsPbI3 to P3HT by comparing the hot carrier cooling dynamics in CsPbI3 without and with P3HT as a hole extracting layer. Our findings indicate a potential of perovskite CsPbI3 for application to hot carrier solar cells.
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