Perovskites with bandgaps between 1.7 and 1.8 eV are optimal for tandem configurations with crystalline silicon (c-Si) because they facilitate efficient harvest of solar energy. In that respect, achieving a high open-circuit voltage (V OC ) in such wide-bandgap perovskite solar cells is crucial for a high overall power conversion efficiency (PCE). Here, we provide key insights into the factors affecting the V OC in wide-bandgap perovskite solar cells. We show that the influence of the hole transport layer (HTL) on V OC is not simply through its ionization potential but mainly through the quality of the perovskite−HTL interface. With effective interface passivation, we demonstrate perovskite solar cells with a bandgap of 1.72 eV that exhibit a V OC of 1.22 V. Furthermore, by combining the high-V OC perovskite solar cell with a c-Si solar cell, we demonstrate a perovskite−Si four-terminal tandem solar cell with a PCE of 27.1%, exceeding the record PCE of single-junction Si solar cells.

p-Conjugated push-pull molecules based on triphenylamine and1 ,1,4,4-tetracyanobuta-1,3-diene (TCBD) have been functionalized with different terminal arene units. In solution, these highly TCBD-twisted systemss howeda strong internal charge transfer band in the visible spectrum and no detectable photoluminescence (PL). Photophysical and theoretical investigations revealed very short singlet excited state deactivation time of % 10 ps resulting from significant conformational changes of the TCBD-arene moiety upon photoexcitation, opening ap athway for non-radiative decay.T he PL was recovered in vacuum-processed films or when the moleculesw ere dispersed in aP MMA matrix leading to as ignificant increase of the excited state deactivation time. As shown by cyclic voltammetry,t hese molecules can act as electron donors compared to C 60 .H ence, vacuum-processedp lanar heterojunction organic solar cells were fabricated leading to am aximum power conversion efficiency of ca. 1.9 %w hich decreases with the increaseo ft he arene size.

No abstract

Triphenylamine-based small push–pull molecules have recently attracted substantial research attention due to their unique optoelectronic properties. Here, we investigate the excited state de-excitation dynamics and exciton diffusion in TPA-T-DCV-Ph-F small molecule, having simple chemical structure with asymmetrical architecture and end-capped with electron-withdrawing p-fluorodicyanovinyl group. The excited state lifetime in diluted solutions (0.04 ns in toluene and 0.4 ns in chloroform) are found to be surprisingly shorter compared to the solid state (3 ns in PMMA matrix). Time-dependent density functional theory indicates that this behavior originates from non-radiative relaxation of the excited state through a conical intersection between the ground and singlet excited state potential energy surfaces. Exciton diffusion length of ~ 16 nm in solution processed films was retrieved by employing time-resolved photoluminescence volume quenching measurements with Monte Carlo simulations. As means of investigating the device performance of TPA-T-DCV-Ph-F, we manufactured solution and vacuum processed bulk heterojunction solar cells that yielded efficiencies of ~ 1.5% and ~ 3.7%, respectively. Our findings demonstrate that the short lifetime in solutions does not hinder per se long exciton diffusion length in films thereby granting applications of TPA-T-DCV-Ph-F and similar push–pull molecules in vacuum and solution processable devices.

In recent years, the dielectric constant (εr) of organic semiconductors (OSCs) has been of interest in the organic photovoltaic (OPV) community due its potential influence on the exciton binding energy....