Predicting Solar Cell Performance from Terahertz and Microwave Spectroscopy

Abstract

Mobilities and lifetimes of photogenerated charge carriers are core properties of photovoltaic materials and can both be characterized by contactless terahertz or microwave measurements. Here, the expertise from fifteen laboratories is combined to quantitatively model the current‐voltage characteristics of a solar cell from such measurements. To this end, the impact of measurement conditions, alternate interpretations, and experimental inter‐laboratory variations are discussed using a (Cs,FA,MA)Pb(I,Br)3 halide perovskite thin‐film as a case study. At 1 sun equivalent excitation, neither transport nor recombination is significantly affected by exciton formation or trapping. Terahertz, microwave, and photoluminescence transients for the neat material yield consistent effective lifetimes implying a resistance‐free JV‐curve with a potential power conversion efficiency of 24.6 %. For grainsizes above ≈20 nm, intra‐grain charge transport is characterized by terahertz sum mobilities of ≈32 cm2 V−1 s−1. Drift‐diffusion simulations indicate that these intra‐grain mobilities can slightly reduce the fill factor of perovskite solar cells to 0.82, in accordance with the best‐realized devices in the literature. Beyond perovskites, this work can guide a highly predictive characterization of any emerging semiconductor for photovoltaic or photoelectrochemical energy conversion. A best practice for the interpretation of terahertz and microwave measurements on photovoltaic materials is presented.

Strong absorption and ultrafast localisation in NaBiS2 nanocrystals with slow charge-carrier recombination

“…On the other hand, self-trapped holes in the localised states can relax much more slowly, owing to the stabilisation from the strong polaron binding energy, which impedes non-radiative recombination and thus leads to the extremely slow decay of the broadband GSB signals in long-time TA measurements. We note that similar results would be expected in the case of bulk disordered NaBiS 2 films, though likely with differences in the localisation rates, due to the potentially weaker geometric confinement 51 , as well as the effects of greatly-reduced surface area, or different synthesis conditions on the degree of cation heterogeneity.…”

Silver‐Bismuth Based 2D Double Perovskites (4FPEA)4AgBiX8 (X = Cl, Br, I): Highly Oriented Thin Films with Large Domain Sizes and Ultrafast Charge‐Carrier Localization

“…Therefore, our measurements reveal that the mobility after localization is < 0.1 cm 2 V −1 s −1 . [ 65 ] The observation of this low mobility supports the predictions of low electronic dimensionality for silver‐bismuth halide elpasolites, which extended to bi‐dimensional layers implies the complete electronic de‐coupling of [Ag X 6 ] 5– and [Bi X 6 ] 3– octahedra (i.e., holes are localized on [Ag X 6 ] 5– octahedra, which are surrounded by [BiX 6 ] 3– octahedra, thus hindering the charge‐carrier hopping – and vice‐versa for electrons). [ 66,67 ]…”

Accelerating research on novel photovoltaic materials

“…The gure also shows the best reported device efficiencies for CIGSe, CdTe, HaP and CZTSe, indicating "effective" carrier lifetimes between 1 ns to 1 ms for the different materials, in fact consistent with reports in the literature. 21,[35][36][37] It is interesting to evaluate what carrier lifetime would be needed for a 20% device efficiency, under these material/device assumptions, which is shown in Fig. 3c.…”

“…20 As an example, we recently showed in a interlab-collaboration between 15 groups how mobility measurements by Thz spectroscopy and microwave conductivity characterization of halide perovskites can yield signicant differences despite being performed on identical samples. 21 Third, we urgently need digitization of data, in the sense that data are made digitally available, and conform to the FAIR principles. The FAIR data concept was introduced by Wilkinson et al in 2016 and proposed basic principles to promote the reuse of scholarly data, both by machines and individuals.…”