Abstract
Hot carrier (HC) cooling accounts for the significant energy loss in lead halide perovskite (LHP) solar cells. Here, we study HC relaxation dynamics in Mn-doped LHP CsPbI3 nanocrystals (NCs), combining transient absorption spectroscopy and density functional theory (DFT) calculations. We demonstrate that Mn2+ doping (1) enlarges the longitudinal optical (LO)–acoustic phonon bandgap, (2) enhances the electron–LO phonon coupling strength, and (3) adds HC relaxation pathways via Mn orbitals within the bands. The spectroscopic study shows that the HC cooling process is decelerated after doping under band-edge excitation due to the dominant phonon bandgap enlargement. When the excitation photon energy is larger than the optical bandgap and the Mn2+ transition gap, the doping accelerates the cooling rate owing to the dominant effect of enhanced carrier–phonon coupling and relaxation pathways. We demonstrate that such a phenomenon is optimal for the application of hot carrier solar cells. The enhanced electron–LO phonon coupling and accelerated cooling of high-temperature hot carriers efficiently establish a high-temperature thermal quasi-equilibrium where the excessive energy of the hot carriers is transferred to heat the cold carriers. On the other hand, the enlarged phononic band-gap prevents further cooling of such a quasi-equilibrium, which facilitates the energy conversion process. Our results manifest a straightforward methodology to optimize the HC dynamics for hot carrier solar cells by element doping.
Highlights
In a single-junction solar cell, the rapid cooling of the hot carrier (HC) excited by photons with energy well above the bandgap is a major energy loss channel responsible for the Shockley–Queisser (SQ) limit.[1]
Both pristine CsPbI3 and Mn-doped CsPbI3 NCs were synthesized by a reported hot-injection method.[23]
No dopantrelated absorption/emission bands can be observed since the Mn d orbitals are not located within the bandgap of CsPbI3.24
Summary
In a single-junction solar cell, the rapid cooling of the hot carrier (HC) excited by photons with energy well above the bandgap is a major energy loss channel responsible for the Shockley–Queisser (SQ) limit.[1]. We interpret the excitation energydependent role of Mn doping in the HC cooling dynamics observed in Fig. 4 from the intrinsic electronic/phononic structure of the doped NCs. We rst revealed the electronic band structure of the samples via DFT calculations, as shown in
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