A major bottleneck delaying the further commercialization of thin-film solar cells based on hybrid organohalide lead perovskites is interface loss in state-of-the-art devices. We present a generic interface architecture that combines solution-processed, reliable, and cost-efficient hole-transporting materials without compromising efficiency, stability, or scalability of perovskite solar cells. Tantalum-doped tungsten oxide (Ta-WO )/conjugated polymer multilayers offer a surprisingly small interface barrier and form quasi-ohmic contacts universally with various scalable conjugated polymers. In a simple device with regular planar architecture and a self-assembled monolayer, Ta-WO -doped interface-based perovskite solar cells achieve maximum efficiencies of 21.2% and offer more than 1000 hours of light stability. By eliminating additional ionic dopants, these findings open up the entire class of organics as scalable hole-transporting materials for perovskite solar cells.

Sustainable biomass production is expected to be one of the major supporting pillars for future energy supply, as well as for renewable material provision. Algal beds represent an exciting resource for biomass/biofuel, fine chemicals and CO 2 storage. Similar to other solar energy harvesting techniques, the efficiency of algal photosynthesis depends on the spectral overlap between solar irradiation and chloroplast absorption. Here we demonstrate that spectral conversion can be employed to significantly improve biomass growth and oxygen production rate in closed-cycle algae reactors. For this purpose, we adapt a photoluminescent phosphor of the type Ca 0.59 Sr 0.40 Eu 0.01 S, which enables efficient conversion of the green part of the incoming spectrum into red light to better match the Q y peak of chlorophyll b. Integration of a Ca 0.59 Sr 0.40 Eu 0.01 S backlight converter into a flat panel algae reactor filled with Haematococcus pluvialis as a model species results in significantly increased photosynthetic activity and algae reproduction rate.

Thin‐film solar cell based on hybrid perovskites shows excellent light‐to‐power conversion efficiencies exceeding 22%. However, the mixed ionic‐electronic semiconductor hybrid perovskite exhibits many unusual properties such as slow photocurrent instabilities, hysteresis behavior, and low‐frequency giant capacitance, which still question us so far. This study presents a direct surface functionalization of transparent conductive oxide electrode with an ultrathin ≈2 nm thick phosphonic acid based mixed C60/organic self‐assembled monolayer (SAM) that significantly reduces hysteresis. Moreover, due to the strong phosphonates bonds with indium tin oxide (ITO) substrates, the SAM/ITO substrates also exhibit an excellent recyclability merit from the perspective of cost effectiveness. Impedance studies find the fingerprint of an ion‐based diffusion process in the millisecond to second regime for TiO2‐based devices, which, however, is not observed for SAM‐based devices at these low frequencies. It is experimentally demonstrated that ion migration can be considerably suppressed by carefully engineering SAM interfaces, which allows effectively suppressing hysteresis and unstable diode behavior in the frequency regime between ≈1 and 100 Hz. It is suggested that a reduced density of ionic defects in combination with the absence of charge carrier accumulation at the interface is the main physical origin for the reduced hysteresis.

With the aim of fully utilizing the low processing temperatures of perovskite solar cells, signifi cant progress in replacing high temperature processed TiO 2 by various low-temperature solution processed electron transporting layers (LT-ETLs) was recently reported. Here, recent progress in the development of LT-ETLs for regular planar structure perovskite solar cells, which is essential for achieving high effi ciency in parallel to avoiding hysteresis, is reviewed. In addition, the application of a novel hysteresis-free LT-ETLs for regular planar perovskite solar cells in our laboratory is briefl y discussed. By incorporating a low temperature processed WO x nanoparticular layer in combination with a mixed fullerene functionalized self-assembled monolayers (SAMs), a regular, planar structure, and hysteresis-free perovskite solar cell with a maximum effi ciency of almost 15% can be fabricated.

Current-voltage hysteresis is a major issue for normal architecture organo-halide perovskite solar cells. In this manuscript we reveal a several-angstrom thick methylammonium iodide-rich interface between the perovskite and the metal oxide. Surface functionalization via self-assembled monolayers allowed us to control the composition of the interface monolayer from Pb poor to Pb rich, which, in parallel, suppresses hysteresis in perovskite solar cells. The bulk of the perovskite films is not affected by the interface engineering and remains highly crystalline in the surface-normal direction over the whole film thickness. The subnanometer structural modifications of the buried interface were revealed by X-ray reflectivity, which is most sensitive to monitor changes in the mass density of only several-angstrom thin interfacial layers as a function of substrate functionalization. From Kelvin probe force microscopy study on a solar cell cross section, we further demonstrate local variations of the potential on different electron-transporting layers within a solar cell. On the basis of these findings, we present a unifying model explaining hysteresis in perovskite solar cells, giving an insight into one crucial aspect of hysteresis for the first time and paving way for new strategies in the field of perovskite-based opto-electronic devices.