Predicting solar cell performance from terahertz and microwave spectroscopy

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

THz spectroscopy of dicyanobenzenes

THz absorption spectra of dicyanobenzene isomers exhibit ~10-fold enhanced absorption cross-sections compared to other measured organic systems. Observed internal and intermolecular features are readily assigned by comparing solid spectra to solution spectra and DFT calculations

Time-resolved infrared absorption study of cyclopentadienyl manganese tricarbonyl derivatives: Chelation of pendant sulfides in acetonitrile

The chelation dynamics of [Mn{η 5-C 5H 4C(O)R}(CO) 3] complexes 1 (R = CH 2(SCH 3)), 2 (R = CH(SCH 3) 2), and 3 (R = C(SCH 3) 3) in room-temperature acetonitrile solution have been investigated on the picosecond time scale by UV-pump IR-probe transient absorption spectroscopy. Similar to the previously observed behavior in n-heptane solution, irradiation of 3 in acetonitrile at 289 nm induces CO loss to exclusively yield a Mn-S chelated dicarbonyl product. Unlike the behavior of 1 and 2 in n-hexane and n-heptane solutions, UV excitation of either 1 or 2 in acetonitrile solution induces CO loss to also exclusively yield the chelated products, with no evidence of a competing solvation pathway. All three complexes exhibit ultrafast chelation in \u3c13 ps. Faster vibrational cooling in acetonitrile vs alkane solutions suggests stronger solute-solvent interaction, perhaps via hydrogen bonding. Ring-opening resulting from continuous irradiation of the pendant sulfide\u27s chelates, [Mn{η 5-C 5H 4C(O)CH(SCH 3) 2-κS}(CO) 2] (4) and [Mn{η 5-C 5H 4C(O)C(SCH 3) 3-κS}(CO) 2] (5), is also discussed. © 2006 American Chemical Society

Intrinsic photoconductivity of P3HT films measured by time-resolved THz spectroscopy

Intrinsic photoconductivities of P3HT polymers were measured and compared by using optical pump-THz probe spectroscopy. The charge carrier mobility shows a clear dependence on the molecular weight and dispersion index of the polymers

Photoconductivity of organic semiconductor polymers studied by time-resolved THz-TDS

This study employs optical-pump terahertzprobe time-domain spectroscopy to measure relative carrier mobilities of semiconductor organic polymer films of poly-3-hexylthiophene (P3HT) and poly(2,5-bis(3-tetradecylthiophen-2-yi) thieno[3,2-b]thiophene) (PBTTT) polymers and these results directly correlate to recently reported electrical device mobility measurements.. An approximately four-fold increase in mobility of P3HT is observed with molecular weight increase from c.a. 18 kD to 150 kD where the intrinsic film mobility saturates for molecular weight > 70 kD. The decay dynamics studies of these polymers showed almost no dependence on the molecular weight of the polymer. The studies also showed an order of magnitude increase in mobility between as cast P3HT films and annealed PBTTT films supporting a strong conjugation length effect. We also measured the mobility dependence on the film quality that is affected by regularity of the polymer, dispersing solvent, electron acceptor traps, and other film growth related parameters relevant to device manufacturing