Spectrum-Splitting Diffractive Optical Element of High Concentration Factor and High Optical Efficiency for Three-Junction Photovoltaics

A spectrum-splitting and beam-concentrating （SSBC） diffractive optical element （DOE） for three-junction pho- tovoltaics （PV） system is designed and fabricated by five-circ/e micro-fabrication. The incident solar light is efficiently split into three sub-spectrum ranges and strongly concentrated on the focal plane, which can be di- rectly utilized by suitable spectrum-matching solar cells. The system concentration factor reaches 12x. Moreover, the designed wavelengths （450nm, 550nm and 65Onto） are spatially distributed on the focal plane, in good agree- ment with the theoretical results. The average optical effic/ency of all the cells over the three designed wavelengths is 60.07%. The SSBC DOE with a high concentration factor and a high optical efficiency provides a cost-effective approach to achieve higher PV conversion efficieneies.

Side-chain fluorination on the pyrido[3,4-b]pyrazine unit towards efficient photovoltaic polymers

A series of new polymer donors (PT-PP, PT-2fPP and PT-4fPP) were synthesized based on alkylthiophene substituted benzodithiophene (BDT-T) and pyrido[3,4-b]pyrazine (PP) building blocks and the effects of fluorination on the polymer properties were explored. Photophysical properties, charge mobilities and morphologies of the three polymers have been intensively investigated. The results indicated that the introduction of the fluorine atom at meta-positions of phenyl substituted PP unit hardly affected their highest occupied molecular orbital (HOMO) level. More importantly, controlling the degree of side-chain fluorination in the polymers is crucial for optimizing the blend morphology. Three polymers showed different photovoltaic properties. The polymer solar cell (PSC) based on the single layer device structure of ITO/PEDOT:PSS/PT-4fPP:PC71BM (1:1, w:w)/ZrAcac/Al demonstrates a high power conversion efficiency (PCE) of 7.61% under the illumination of AM 1.5G,100 mW cm-2, which is the highest value for PP-based PSCs.

“Mutually Doped”Conjugated Polyelectrolyte-Polyoxometalate Complex as Hole Transporting Material for Efficient Organic Solar Cells

Comprehensive Summary Compared to electron transporting layer materials,the species and numbers of hole transporting layer(HTL)materials for organic solar cells(OSCs)are rare.The development of HTL materials with excellent hole collection ability and non-corrosive nature is a long-standing issue in the field of OSCs.Herein,we designed and synthesized a series of conjugated polyelectrolytes(CPEs)with continuously varied energy levels toward HTL materials for efficient OSCs.Through a“mutual doping”treatment,we obtained a CPE composite PCT-F:POM with a WF of 5.48 eV and a conductivity of 1.56х10^(-3)S/m,meaning that a good hole collection ability can be expected for PCT-F:POM.The OSC modified by PCT-F:POM showed a high PCE of 18.0%,which was superior to the reference device with PEDOT:PSS.Moreover,the PCT-F:POM-based OSC could maintain 91%of the initial PCE value after storage of 20 d,meaning that the long-term stability of OSCs is improved by incorporating the PCT-F:POM HTL.In addition,PCT-F:POM possesses good compatibility with large-area processing technique;i.e.,a PCT-F:POM HTL was processed by the blade-coating method for fabricating 1 cm^(2)OSC,and a PCE of 15.1%could be achieved.The results suggest the promising perspective of PCT-F:POM in practical applications.