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Effective masses are calculated for a large variety of perovskites of the form ABX3 differing in chemical composition (A= Na, Li, Cs; B = Pb, Sn; X= Cl, Br, I) and crystal structure. In addition, the effects of some defects and dopants are assessed. We show that the effective masses are highly correlated with the energies of the valence-band maximum, conduction-band minimum, and band gap. Using the k·p theory for the bottom of the conduction band and a tight-binding model for the top of the valence band, this trend can be rationalized in terms of the orbital overlap between halide and metal (B cation). Most of the compounds studied in this work are good charge-carrier transporters, where the effective masses of the Pb compounds (0 < mh∗ < me∗ < 1) are systematically larger than those of the Sn-based compounds (0 < mh∗ ≈ me∗ < 0.5). The effective masses show anisotropies depending on the crystal symmetry of the perovskite, whether orthorhombic, tetragonal, or cubic, with the highest anisotropy for the tetragonal phase (ca. 40%). In general, the effective masses of the perovskites remain low for intrinsic or extrinsic defects, apart from some notable exceptions. Whereas some dopants, such as Zn(II), flatten the conduction-band edges (me∗ = 1.7m0) and introduce deep defect states, vacancies, more specifically Pb2+ vacancies, make the valence-band edge more shallow (mh∗ = 0.9m0). From a device-performance point of view, introducing modifications that increase the orbital overlap [e.g., more cubic structures, larger halides, smaller (larger) monovalent cations in cubic (tetragonal/orthorhombic) structures] decreases the band gap and, with it, effective masses of the charge carriers.

The water splitting performance of hematite photoanodes is explored under a wide range of light intensities. The photocurrent scales linearly and the photovoltage scales logarithmically with the intensity, showing steeper rate than in photovoltaics, probably due to the enhanced ratio between charge transfer and recombination at high intensities. Hence, light concentration serves as another handle to enhance the efficiency of hematite photoanodes.

High extinction coefficients and easily tunable spectral properties of π- conjugated donor-acceptor dyes are of superior advantage for the design of new metalfree organic sensitizers for applications in dye-sensitized solar cells. Ultrafast transient absorption spectroscopy on the femtosecond and nanosecond time scales provided deep insights into the dependence of charge carrier dynamics in fully organic dye/TiO2 systems on i) the donor-acceptor distance, ii) the π-conjugation length, and iii) the coupling to TiO2 by different anchoring groups. Importantly, the observed differences in charge transfer dynamics justify the variations of photovoltaic performances of the dyes as applied in solar cell devices. This leads to the conclusion that the photoconversion efficiencies strongly depend on a delicate interplay between the dyes’ building blocks, i.e. the donor, the π-conjugated spacer and the anchor/acceptor moieties, and may easily be tuned by molecular design.