High Open Circuit Voltage in Regioregular Narrow Band Gap Polymer Solar Cells

Abstract

The regioregular narrow band gap (E(g) ~1.5 eV) conjugated polymer PIPCP was designed and synthesized. PIPCP contains a backbone comprised of CPDT-PT-IDT-PT repeat units (CPDT = cyclopentadithiophene, PT = pyridyl[2,1,3]thiadiazole, IDT = indacenodithiophene) and strictly organized PT orientations, such that the pyridyl N-atoms point toward the CPDT fragment. Comparison of PIPCP with the regiorandom counterpart PIPC-RA illustrates that the higher level of molecular order translates to higher power conversion efficiencies (PCEs) when incorporated into bulk heterojunction (BHJ) organic solar cells. Examination of thin films via absorption spectroscopy and grazing incidence wide-angle X-ray diffraction (GIWAXS) experiments provides evidence of higher order within thin films obtained by spin coating. Most significantly, we find that PIPCP:PC61BM blends yield devices with an open circuit voltage (V(oc)) of 0.86 V, while maintaining a PCE of ~6%. Comparison against a wide range of analogous narrow band gap conjugated polymers reveals that this V(oc) value is particularly high for a BHJ system with band gaps in the 1.4-1.5 eV range thereby indicating a very low E(g) - eV(oc) loss.

Thieno[3,4‐c]Pyrrole‐4,6‐Dione‐Based Polymer Acceptors for High Open‐Circuit Voltage All‐Polymer Solar Cells

“…[30] noting that Eloss values ≤0.5 eV are especially difficult to achieve in fullerene-based BHJ devices. [66][67][68] The notable differences in JSC values achieved in optimized P2TPD[2F]T-and P2TPDBT[2F]T-based BHJ solar cells (Table 2) are emphasized in the J-V curves shown in Figure 5a, and reflected in the external quantum efficiency (EQE) spectra provided in Figure 5b; Devices with optimized PBDT-TS1:Polymer_Acceptor ratio of 1:2 (wt/wt); solution-cast from chloroform (CF). Figure S16).…”

Deep Absorbing Porphyrin Small Molecule for High-Performance Organic Solar Cells with Very Low Energy Losses

“…For BHJ OSCs, the minimum E loss was suggested to be 0.6 eV, 11 and the corresponding V oc is often used as the achievable maximum V oc . However, the E loss values below 0.6 eV are still rare even for PSCs 13,14 and no such report for small molecule-based OSCs. It also should be noted that, though low energy losses below 0.6 eV were sometimes reported for PSCs, their performance often dropped dramatically when reducing E loss to below 0.6 eV.…”

Improved open-circuit voltage of benzodithiophene based polymer solar cells using bulky terthiophene side group

“…For polymer PQ3 (compared with PDPP-BDT) and PQ4 (compared with PBDT TEH -DT H BTff), PQ3 and PQ4 show almost the same E g with PDPP-BDT and PBDT TEH -DT H BTff, but much higher V oc and much lower E g ÀeV oc (Table 4). To highlight the high V oc feature of devices, researchers define the donor photon energy loss as E g À eV oc , where E g is the optical band gap of the donor polymer and V oc is obtained from the corresponding device with either PC 61 BM or PC 71 BM [51]. Especially, we note that PQ3 shows E g À eV oc ¼0.51, which is almost the lowest E g À eV oc value achieved by researchers up to now [51,52].…”

“…To highlight the high V oc feature of devices, researchers define the donor photon energy loss as E g À eV oc , where E g is the optical band gap of the donor polymer and V oc is obtained from the corresponding device with either PC 61 BM or PC 71 BM [51]. Especially, we note that PQ3 shows E g À eV oc ¼0.51, which is almost the lowest E g À eV oc value achieved by researchers up to now [51,52]. This indicates that PQ3 is such a good photovoltaic polymer that can produce V oc $0.78V with a low E g $1.29 eV.…”