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Halide perovskites have shown excellent photophysical properties for solar cell applications which led to a rapid increase of the device efficiency. Understanding the charge carrier dynamics within the active perovskite absorber and at its interfaces will be key to further progress in their development. Here we present a series of fully evaporated devices employing hole transport materials with different ionization energies. The open circuit voltage of the devices, along with their ideality factors, confirm that the former is mainly determined by the bulk and surface recombination in the perovskite, rather than by the energetic offset between the valence band of the perovskite and the highest occupied molecular orbital of the organic transport layers. These results help to further understand the origin of the open circuit potential in perovskite solar cells, which is an important parameter that needs to be improved to further boost power conversion efficiencies.

The molecular-level arrangement of the donor and acceptor (i.e. the local morphology) in organic solar cells governs charge separation and charge transport via its effect on the mobility of charges. However, the nanometre-scale mobility in such systems, which can be measured using terahertz (THz) spectroscopy, has been little investigated at relevant low excitation densities, due to extremely weak signals. Here, we study the mobility over short distances and at ultrashort times using time-resolved optical-pump-THz-probe (OPTP) spectroscopy on pBTTT:PCBM blends. This complements our previous results obtained with transient absorption (TA) and electro-modulated differential absorption (EDA) techniques. In the pBTTT:PCBM system, the co-existence of fullerene-/polymer-rich (‘neat’) and co-crystalline (‘intermixed’) regions can be controlled through choice of composition (weight ratio of the two components, use of processing additive). We demonstrate high short-range mobilities that help charges separate, and we show how this mobility of photogenerated charges develops in time, in particular as the charges move between different phase regions of the blend. By reducing the pump fluence below the threshold for nonlinear recombination mechanisms, we access these properties at solar cell operating conditions. Overall, we explain the necessity of different local phases through their influence on charge lifetime and mobility.

Hybrid organic–inorganic metal perovskites have emerged as highly promising materials for solar energy conversion. However, key questions regarding the working principles of perovskite solar cells remain to be answered in order to improve the design of such devices. In the present study, we have investigated the influence of excess excitation energy on the initial photo-products generated from FTO/meso-TiO2/CH3NH3PbI3 samples. We find that upon resonant excitation at the band edge, part of the formation of free charges passes via an excitonic state that dissociates on the sub-picosecond time scale. An exciton binding energy of

Light-induced charge formation is essential for the generation of photocurrent in organic solar cells. In order to gain a better understanding of this complex process, we have investigated the femtosecond dynamics of charge separation upon selective excitation of either the fullerene or the polymer in different bulk heterojunction blends with well-characterized microstructure. Blends of the pBTTT and PBDTTPD polymers with PCBM gave us access to three different scenarios: either a single intermixed phase, an intermixed phase with additional pure PCBM clusters, or a three-phase microstructure of pure polymer aggregates, pure fullerene clusters and intermixed regions. We found that ultrafast charge separation (by electron or hole transfer) occurs predominantly in intermixed regions, while charges are generated more slowly from excitons in pure domains that require diffusion to a charge generation site. The pure domains are helpful to prevent geminate charge recombination, but they must be sufficiently small not to become exciton traps. By varying the polymer packing, backbone planarity and chain length, we have shown that exciton diffusion out of small polymer aggregates in the highly efficient PBDTTPD:PCBM blend occurs within the same chain and is helped by delocalization.

Herein is reported an investigation towards the stereoselective synthesis of inherently chiral pseudorotaxanes. Chiral ammonium threads were readily prepared in five steps from racemic or enantiopure (M or P) salts of di-n-propyl-1,13-dimethoxyquinacridinium cation. Their self-assembly with DB24C8 or disymmetrically oriented DB24C8F6 rings formed pseudorotaxanes as shown by 1H and 19F NMR spectroscopy as well as MS measurements. A determination of the association constants (Ka) was afforded. The crucial role played by the ammonium counter-ion in the threading process was further demonstrated as salts of TRISPHAT (tris(tetrachlorobenzenediolato)phosphate(V)) anion were quite more effective than their PF6- analogues (x 7.3). A general lack of diastereoselectivity (de

The objective of this study was to evaluate the possibility of photoinduced stack/rod electron transfer in surface "zipper" architectures composed of stacks of blue (B) naphthalenediimides (NDIs) along strings of oligophenylethynyl (OPE) rods. The synthesis and characterization of anionic and cationic multichromophoric OPE-B systems are reported. Absorption spectra suggest that in OPE-B systems, planarity and thus absorption and conductivity of the OPE can possibly be modulated by intramolecular stacking of the surrounding NDIs, although interfering contributions from aggregation remain to be differentiated. Among surface architectures constructed with OPE-B and POP-B systems by zipper and layer-by-layer (LBL) assembly, photocurrents generated by OPE-B zippers exhibit the best critical thickness and fill factors. These findings confirm the existence and functional relevance of topologically matching zipper architectures. In OPE-B zippers, OPEs generate much more photocurrent than the blue NDIs. Ultrafast electron transfer from OPEs to NDIs accounts for these photocurrents, providing wavelength-controlled access to rod–stack charge separation, and thus to formal supramolecular n/p-heterojunctions (SHJs). NDI excitation is not followed by the complementary hole transfer to the OPE rod. Scaffolds with higher HOMOs will be needed to integrate blue NDIs into SHJ photosystems.