Solution‐processed tandem polymer solar cells with an inverted polarity configuration provide a power conversion efficiency of 5.8%. The tandem cells use an almost loss‐free recombination layer and two photoactive layers, with wide and small bandgaps, to increase the power conversion efficiency beyond that of the corresponding single‐layer cells.

A triple junction polymer solar cell in a novel 1 + 2 type configuration provides photoelectrochemical water splitting in its maximum power point at V ≈ 1.70 V with an estimated solar to hydrogen energy conversion efficiency of 3.1%. The triple junction cell consists of a wide bandgap front cell and two identical small bandgap middle and back cells.

To improve the thermal stability of polymer:fullerene bulk heterojunction solar cells, a new polymer, poly[2-methoxy-5-(2 0 -phenylethoxy)-1,4phenylenevinylene] (MPE-PPV), has been designed and synthesized, which showed an increased glass transition temperature (T g ) of 111 °C. The thermal characteristics and phase behavior of MPE-PPV:[6,6]-phenyl C 61 -butyric acid methyl ester ([60]PCBM) blends were investigated by means of modulated temperature differential scanning calorimetry and rapid heatingÀcooling calorimetry. The thermal stability of MPE-PPV:[60]PCBM solar cells was compared with devices based on the reference MDMO-PPV material with a T g of 45 °C. Monitoring of the photo-currentÀvoltage characteristics at elevated temperatures revealed that the use of high-T g MPE-PPV resulted in a substantial improvement of the thermal stability of the solar cells. Furthermore, a systematic transmission electron microscope study of the active polymer:fullerene layer at elevated temperatures likewise demonstrated a more stable morphology for the MPE-PPV:[60]PCBM blend. Both observations indicate that the use of high-T g MPE-PPV as donor material leads to a reduced free movement of the fullerene molecules within the active layer of the photovoltaic device. Finally, optimization of the PPV:fullerene solar cells revealed that for both types of devices the use of [6,6]-phenyl C 71 -butyric acid methyl ester ([70]PCBM) resulted in a substantial increase of current density and power conversion efficiency, up to 3.0% for MDMO-PPV:[70]PCBM and 2.3% for MPE-PPV:[70]PCBM.

An organic artificial leaf that is composed of a triple junction polymer solar cell for light absorption and low-overpotential catalytic electrodes for hydrogen and oxygen evolution provides solar-to-hydrogen conversion efficiency of 4.9% using earth-abundant catalysts.