Measuring the current density - voltage characteristics of individual subcells in two-terminal polymer tandem solar cells

Measuring the current density to voltage (J–V) characteristics of the separate subcells in two-terminal polymer tandem solar cells enables assessing the individual contributions of the two subcells to the total performance. We present two different methods to determine the J–V characteristics of the subcells in a two-terminal tandem cell without interfering with the light incoupling of the cell. The first method employs an extra proximity metal electrode that acts as a voltage probe. The proximity electrode is in contact with the recombination layer that separates the two subcells, but is positioned outside the illuminated area of the tandem cell. The second method uses bias-dependent external quantum efficiency measurements of two-terminal tandem solar cells and subsequent integration with the solar spectrum to determine the J–V curves of the subcells. The methods show good mutual agreement. For a 4.7% efficient solution processed two-terminal polymer tandem cell, based on PFTBT:PCBM as wide band gap and pBBTDPP2:PCBM as small band gap layer, we find that the subcells contribute with efficiencies of 2.9% and 1.8%

Fused ring thiophene-based poly(heteroarylene ethynylene)s for organic solar cells

Alternating small band gap p-conjugated polymers consisting of alkylated cyclopentadithiophene or dithienopyrrole units linked via ethynylene bonds to 2,3-diphenylthieno[3,4-b]pyrazine or 2,1,3-benzothiadiazole have been prepared in high yields by Sonogashira condensation polymerization. The copolymers were characterized by NMR, GPC, UV–vis, and cyclic voltammetry. In thin films these polymers exhibit an optical band gap of 1.46-1.72 eV. In bulk heterojunction solar cells with PCBM as an acceptor these donor polymers provide estimated power conversion efficiencies of 1.34-1.74%. Because of the ethynylene bonds, the polymers lead to the solar cells with a relatively high open circuit voltage (0.72-0.82 V) in relation to the reduced optical band gap, which helps in reducing energy losses

Double and triple junction polymer solar cells processed from solution

Multiple junction solar cells incorporating polymer:fullerene bulk heterojunctions as active layers and soln. processed electron and hole transport layers are presented. The recombination layer, deposited between the active layers, is fabricated by spin coating ZnO nanoparticles from acetone, followed by spin coating neutral pH poly(3,4-ethylenedioxythiophene) from water and short UV illumination of the completed device. The key advantage of this procedure is that each step does not affect the integrity of previously deposited layers. The open-circuit voltage (Voc) for double and triple junction solar cells is close to the sum of the Voc's of individual cells. [on SciFinder (R)

Digitally printed photovoltaic devices with increasing stack complexity

Digital printing of organic photovoltaic devices is presented as a viable option for the creation of increasingly complex device structures. Fully printed organic tandem junction devices were made that show a perfect summation of the open circuit voltages of the subcells. These results show the feasibility of complete digitally printed device stacks providing product designers with unprecedented freedom of design for integration of a photovoltaic functionality in new products