still far behind those of inorganic counterparts, such as sc-Si, GaAs, CdTe, CIGS, and Perovskite solar cells. [ 2 ] One of the main reasons is their low open-circuit voltage ( V oc ) due to the large energy loss per absorbed photon. The minimum energy loss ( E loss ) is defi ned by the equation: E loss = E g − qV oc , where E g is the optical gap of the main light absorber, in most cases the donor material. Decreasing E loss will enhance the V oc and thus PCEs of PSCs. [3][4][5] The minimum E loss for efficient charge generation in organic solar cells (OSCs) is suggested to be 0.6 eV, [ 6 ] and E loss below 0.6 eV often leads to ineffi cient charge generation and low quantum effi ciency, limiting the photocurrent and PCEs. [ 7 ] Typically, the E loss for polymer:fullerene based PSCs with high PCEs of 9%−11% is between 0.7 and 0.9 eV. [8][9][10] In contrast, Perovskite solar cells have a high V oc (> 1 V) with E loss of ≈0.5 eV, which partially accounts for their much higher PCEs of ≈20%. [ 11,12 ] The E loss values for inorganic solar cells, such as sc-Si, GaAs, GaInP, CdTe, CIGS-based solar cells are normally between 0.3 and 0.6 eV. [ 13 ] In Figure 1 and Table S1 in the Supporting Information, we summarize a selection of solar cells exhibiting either One of the factors limiting the performance of organic solar cells (OSCs)is their large energy losses ( E loss ) in the conversion from photons to electrons, typically believed to be around 0.6 eV and often higher than those of inorganic solar cells. In this work, a novel low band gap polymer PIDTT-TID with a optical gap of 1.49 eV is synthesized and used as the donor combined with PC 71 BM in solar cells. These solar cells attain a good power conversion effi ciency of 6.7% with a high open-circuit voltage of 1.0 V, leading to the E loss as low as 0.49 eV. A systematic study indicates that the driving force in this donor and acceptor system is suffi cient for charge generation with the low E loss . This work pushes the minimal E loss of OSCs down to 0.49 eV, approaching the values of some inorganic and hybrid solar cells. It indicates the potential for further enhancement of the performance of OSCs by improving their V oc since the E loss can be minimized.

A conjugated donor-acceptor polymer, poly[4,4,9,9-tetrakis(4-hexylphenyl)-4,9-dihydro- s-indaceno[1,2- b:5,6- b']dithiophene-2,7-diyl- alt-5-(2-ethylhexyl)-4 H-thieno[3,4- c]pyrrole-4,6(5 H)-dione-1,3-diyl] (PIDT-TPD), is blended with the fullerene derivative [6,6]phenyl-C61-butyric acid methyl ester (PCBM) for the fabrication of thin and solution-processed organic photodetectors (OPDs). Systematic screening of the concentration ratio of the blend and the molecular weight of the polymer is performed to optimize the active layer morphology and the OPD performance. The device comprising a medium molecular weight polymer (27.0 kg/mol) in a PIDT-TPD:PCBM 1:1 ratio exhibits an external quantum efficiency of 52% at 610 nm, a dark current density of 1 nA/cm, a detectivity of 1.44 × 10 Jones, and a maximum 3 dB cutoff frequency of 100 kHz at -5 V bias. These results are remarkable among the state-of-the-art red photodetectors based on conjugated polymers. As such, this work presents a functional organic active material for high-speed OPDs with a linear photoresponse at different light intensities.

Polymers based on quinoxaline and indacenodithieno[3,2-b]thiophene (IDTT) withmeta-hexyl-phenyl side chains were synthesized.

D–A copolymers incorporating new pyrrolo[3,4-g]quinoxaline-6,8-dione (PQD) building blocks were synthesized for bulk heterojunction solar cells with high photovoltages.