Solid-state, solution processed solar-cells based on organic–inorganic methyl ammonium lead halide absorbers have achieved efficiencies in excess of 15%, which has superseded liquid dye sensitized cells, as well as various thin film-based photovoltaics. This report introduces a new metal-halide perovskite, based on the formamidinium cation (HC(NH2)2 +), that displays a favorable band gap (1.47 eV) and represents a broader absorption compared to previously reported absorbers that contained the methylammonium cation (CH3NH3 +). The high open-circuit voltage (V oc = 0.97 V) and promising fill-factor (FF = 68.7%) yield an efficiency of 4.3%, which make this material an excellent candidate for this new class of perovskite solar cell. This report also investigates the formation of a black trigonal (P3m1) perovskite polymorph and a yellow hexagonal nonperovskite (P63mc) polymorph. Further solar cell development would entail the stabilization of the black trigonal (P3m1) perovskite polymorph over the yellow hexagonal nonperovskite (P63mc) polymorph.

Organic-inorganic metal halide perovskite solar cells were fabricated by laminating films of a carbon nanotube (CNT) network onto a CH3NH3PbI3 substrate as a hole collector, bypassing the energy-consuming vacuum process of metal deposition. In the absence of an organic hole-transporting material and metal contact, CH3NH3PbI3 and CNTs formed a solar cell with an efficiency of up to 6.87%. The CH3NH3PbI3/CNTs solar cells were semitransparent and showed photovoltaic output with dual side illuminations due to the transparency of the CNT electrode. Adding spiro-OMeTAD to the CNT network forms a composite electrode that improved the efficiency to 9.90% due to the enhanced hole extraction and reduced recombination in solar cells. The interfacial charge transfer and transport in solar cells were investigated through photoluminescence and impedance measurements. The flexible and transparent CNT network film shows great potential for realizing flexible and semitransparent perovskite solar cells.

We report a novel electron-rich molecule based on 3,4-ethylenedioxythiophene (H101). When used as the hole-transporting layer in a perovskite-based solar cell, the power-conversion efficiency reached 13.8 % under AM 1.5G solar simulation. This result is comparable with that obtained using the well-known hole transporting material 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD). This is the first heterocycle-containing material achieving >10 % efficiency in such devices, and has great potential to replace the expensive spiro-OMeTAD given its much simpler and cheaper synthesis.

cell (i.e., mesoscopic, meso-superstructured and planar heterojunctions), the power conversion effi ciencies (PCEs) of these cells have improved tremendously from 3.8% to 20% within a few years. [1][2][3][4][5][6][7] The high effi ciencies obtained with the hybrid perovskites are attributed to the high absorbance and long-range balanced charge transport lengths within the hybrid perovskites. [ 8,9 ] While most studies focus on improving the device performance, equal emphasis should also be given to the fundamental device physics. Among the several open questions on perovskite solar cells, the most challenging issue to date is the hysteresis effect (or dynamic lag) in current -voltage ( I-V ) measurements. [ 10,11 ] It was found that the PCEs measured is highly dependent on scan rate, scan direction, scan history, and light exposure. This could lead to the inaccurate reporting of PCEs, which would undermine the credibility and progress of this nascent photovoltaic technology. Consensus on the origin(s) of the hysteresis has proven elusive. Proposed origins include slow trapping and detrapping of charges due to subgap traps of solution-processed perovskites; changes to the ferroelectric structure and ion migration, etc. [10][11][12][13] Detailed investigations are therefore urgently needed to unravel their complicated mechanisms and elucidate their physical origins. Such fi ndings would be highly essential for establishing clear design rules needed for further performance improvements in halide organic-inorganic perovskite solar cells.The electrical properties and optical properties of an optoelectronic material are intimately coupled; both are the macroscopic refl ection of the intrinsic electronic physics. Studying both the electrical and optical behavior in a photovoltaic device is an ideal approach to uncover the physics shared by the two. Till now, very few reports have concurrently studied the optical and electrical phenomena that occur in perovskite solar cells with hysteresis. Herein, through versatile combined electrical and optical measurements, we uncover that the hysteresis effect in CH 3 NH 3 PbI 3 (MAPbI 3 ):TiO 2 -based perovskite solar cells is dominated by distinct slow processes persisting from hundreds of milliseconds to tens of seconds. These processes originate from the dynamic rearrangement of the perovskite structure that is mediated by applied electric fi elds and accumulated

Spiro is beautiful. Two spiro-type molecules are compared at molecular levelviasingle-crystallography. Through molecular engineering, we synthesized new hole transporting material PST1 which works efficiently in perovskite solar cells without cobalt dopant.

A novel swivel-cruciform 3,3′-bithiophene based hole-transporting material (HTM) with a low lying highest occupied molecular orbital (HOMO) level for application in perovskite solar cells were synthesized.

Two new electron-rich molecules, 2,3,4,5-tetra[4,4'-bis(methoxyphenyl)aminophen-4"-yl]-thiophene (H111) and 4,4',5,5'-tetra[4,4'-bis(methoxyphenyl)aminophen-4"-yl]-2,2'-bithiophene (H112), which contain thiophene cores with arylamine side groups, are reported. When used as the hole-transporting material (HTM) in perovskite-based solar cell devices, power conversion efficiencies of up to 15.4% under AM 1.5G solar simulation were obtained. This is the highest efficiency achieved with HTMs not composed of 2,2',7,7'-tetrakis(N,N'-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD) and its isomers. Both HTMs, especially H111, have great potential to replace expensive spiro-OMeTAD given their much simpler and less expensive syntheses.

diffuse and intermittent nature requires that we combine an effi cient harvesting strategy with an effective method for energy storage before large-scale utilization can be envisioned. Inspired by natural photosynthesis, converting solar energy directly into chemical fuels is considered as one of the most promising ways to solve this challenge. [ 2 ] Among the possible chemical fuels, hydrogen is the simplest form and it can be generated through sunlight-driven water splitting with semiconductor light absorbers in contact with aqueous solutions. [ 3 ] The thermodynamic potentials and kinetic demands of the water splitting reactions strictly defi ne the bandgap energy and the band edge positions required of a semiconductor for photoelectrochemical (PEC) water splitting. Despite tremendous efforts in modifying existing materials and searching for new materials during the past several decades, [ 4 ] there is still no single material that meets all the requirements for effi cient and durable water splitting under solar illumination. Effi cient sunlight-driven water splitting devices can be achieved by pairing two absorbers of different optimized bandgaps in an optical tandem design. With tunable absorption ranges and cell voltages, organic-inorganic metal halide perovskite solar cells provide new opportunities for tailoring top absorbers for such devices. In this work, semitransparent perovskite solar cells are developed for use as the top cell in tandem with a smaller bandgap photocathode to enable panchromatic harvesting of the solar spectrum. Anew CuIn x Ga 1− x Se 2 multilayer photocathode is designed, exhibiting excellent performance for photoelectrochemical water reduction and representing a near-ideal bottom absorber. When pairing it below a semitransparent CH 3 NH 3 PbBr 3 -based solar cell, a solar-to-hydrogen effi ciency exceeding 6% is achieved, the highest value yet reported for a photovoltaic-photoelectrochemical device utilizing a single-junction solar cell as the bias source under one sun illumination. The analysis shows that the effi ciency can reach more than 20% through further optimization of the perovskite top absorber.