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Property modulation of 2,5-dioctylpyrrolo[3,4-c]pyrrole-1,3(2H,5H)-dione (DPPD)-based high energy converting wide band gap polymers, P(BDT-TDPPDT) and P(BDTT-TDPPDT), was studied via the incorporation of an additional DPPD unit on their repeating units. A new electron acceptor (BDPPD) unit containing two DPPD units was prepared and copolymerized with the distannyl derivatives of benzodithiophene (BDT) or 2D-conjugated benzodithiophene (BDTT) to provide two new polymers, P(BDT-BDPPD) and P(BDTT-BDPPD). The optical band gaps and highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) energy levels of P(BDT-BDPPD) and P(BDTT-BDPPD) were 2.16 eV, 2.08 eV and −5.37 eV/‒3.21 eV, −5.44 eV/‒3.36 eV, respectively. The hole mobilities of P(BDT-BDPPD) and P(BDTT-BDPPD) were in the order of 10 −4 cm 2 V −1 s −1 . The polymer solar cells (PSCs) prepared with the configuration of ITO/PEDOT:PSS/P(BDT-BDPPD) or P(BDTT-BDPPD):PC 70 BM/Al gave maximum power conversion efficiencies ( PCEs ) of 2.74% and 3.63%, respectively. The insertion of a BDPPD unit instead of a TDPPDT unit on the DPPD-based polymer backbone did not affect the optical and electrochemical properties considerably. On the other hand, the new polymers, P(BDT-BDPPD) and P(BDTT-BDPPD), resulted in improved photovoltaic performances compared to the reported polymers, P(BDT-TDPPDT) and P(BDTT-TDPPDT), for the devices prepared without additives. [ABSTRACT FROM AUTHOR]

A new approach is presented here to maximize the efficiency of ternary blend polymer solar cells (ter-PSCs). The properties of co-absorbing wide band-gap polymers are fine-tuned via the insertion of two different appropriate electron-acceptor units on their backbone in different ratios, and the resulting polymers are utilized as a co-absorbent on ter-PSCs. The copolymerization of benzodithiophene, pyrrolopyrrole-1,3-dione, and difluoro-benzothiadiazole derivatives at three different ratios, 1.00:1.00:0.00, 1.00:0.50:0.50, and 1.00:0.25:0.75, produces the polymers P1–P3. The absorption bands of P1–P3 are gradually red-shifted, and the band-gaps are reduced. The crystallinity of the polymers is increased in the order of P1 < P2 < P3. The binary polymer solar cells (bi-PSCs) are fabricated using blends of P1 , P2, or P3 with PC 70 BM and provide comparable power conversion efficiencies (PCE s) of 5.41%, 5.55%, and 4.01%, respectively. However, the inclusion of 20 wt% of each of P1 , P2 , and P3 on a P4 (=PTB7-Th):PC 70 BM blend offers PCE s of 9.31%, 9.60%, and 9.85%, respectively, which are higher than that of the bi-PSC made using a blend of P4:PC 70 BM (PCE = 8.20%). The improved absorption, crystallinity, and carrier mobilities of the ternary blends are the main reasons for their enhanced photovoltaic performance compared with the binary blends. Image 1 • The properties of co-absorbing polymers were tuned via main chain modification. • The band-gaps of co-absorbing polymers were varied between 2.11 and 1.71 eV. • The HOMO levels of co-absorbing polymers were varied between −5.38 and −5.26 eV. • The binary PSCs properties of co-absorbing polymers were comparable. • Each co-absorbing polymers displayed different performance on ternary PSCs. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • New polymer, namely P(DTBT-PPD), was prepared. • The E g and HOMO/LUMO levels were 1.64 eV and −5.30 eV/−3.66 eV. • The hole and electron mobilities were 2.06 × 10–4 and 4.70 × 10–5 cm2V−1s−1. • P(DTBT-PPD)-based OSCs gave maximum PCE of 2.23%. • The properties of P(DTBT-PPD) were compared with those of P(BDTT-PPD). Abstract In this study, we investigated the property modulation of a high energy converting, wide-band-gap, alternating polymer, P(BDTT-PPD), comprising benzodithiophene (BDTT) and pyrrolo[3,4-c]pyrrole-1,3(2H,5H)-dione (PPD) derivatives by replacing BDTT with 4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole (DTBT). The new alternating polymer, named P(DTBT-PPD) , was prepared by polymerizing distannyl DTBT and dibromo PPD derivatives, with the aim of making a PPD-based, low-band-gap polymer for solar cell applications. Polymer P(DTBT-PPD) displayed an intense absorption band between 300 and 750 nm with two distinct absorption maxima at 439 and 605 nm as a film. The calculated optical band-gap (E g) was 1.64 eV. The determined highest occupied and lowest unoccupied molecular (HOMO and LUMO, respectively) orbital energy levels of P(DTBT-PPD) were −5.30 and −3.66 eV, respectively. Solution-processed organic solar cells (OSCs), made with P(DTBT-PPD): PC 70 BM ([6,6]-Phenyl C 71 butyric acid methyl ester), provided a maximum power-conversion efficiency (PCE) of 2.23%. P(DTBT-PPD) displayed much lower E g (≈0.4 eV), slightly higher HOMO level (≈0.14 eV), and considerably lower PCE (≈4%), than P(BDTT-PPD). The increased curvature of P(DTBT-PPD) chains could be the main reason for their lower PCE than P(BDTT-PPD). [ABSTRACT FROM AUTHOR]

A new polymer, P(BDT-fPPD) , which incorporates 4,8-bis(2-ethylhexyloxy)benzo[1,2-b:4,5-bʹ]dithiophene (BDT) and 4,6-bis(furan-2-yl)-2,5-dioctylpyrrolo [ 3,4-c]pyrrole-1,3(2H,5H)-dione (fPPD, furan π–bridged PPD) units, was prepared. The optoelectrical, crystalline, charge transport, backbone curvature, and photovoltaic properties of P(BDT-fPPD) were thoroughly studied. P(BDT-fPPD) was also compared to the polymer P(BDT-tPPD) , comprising BDT and 4,6-bis(thiophen-2-yl)-2,5-dioctylpyrrolo [ 3,4-c]pyrrole-1,3(2H,5H)-dione (tPPD, thiophene π–bridged PPD) units. This study demonstrates that the π–bridges, such as thiophene and furan, attached between the BDT and pyrrolo [ 3,4-c]pyrrole-1,3(2H,5H)-dione (PPD) units greatly altered the properties of the resulting polymers. In particular, the backbone curvature of P(BDT-fPPD) was significantly different from that of P(BDT-tPPD) , which resulted in P(BDT-fPPD) having a higher bandgap energy (E g), deeper HOMO level, and higher crystallinity, but lower carrier mobility (μ h) and relatively poor power conversion efficiency (PCE) compared to P(BDT-tPPD). For P(BDT-fPPD), the E g , HOMO, μ h , and PCE were determined as 2.20 eV, −5.44 eV, 1.19 × 10−5 cm−2 V−1 s−1, and 2.62%, respectively. The corresponding values for P(BDT-tPPD) were 2.11 eV, −5.39 eV, 2.95 × 10−4 cm−2 V−1 s−1 and 5.29%, respectively. Interestingly, the inclusion of a small amount of P(BDT-tPPD) in the PTB7-Th:PC 70 BM blend enhanced the PCE of the resulting ternary organic solar cells (OSCs), whereas the insertion of P(BDT-fPPD) lowered the PCE of the ternary OSCs. The lower mobility and PCE obtained for P(BDT-fPPD) are mainly attributed to its poor blending with PC 70 BM. [Display omitted] • New polymer namely P(BDT-fPPD) was prepared. • The properties of P(BDT-fPPD) and P(BDT-tPPD) were compared. • P(BDT-fPPD) and P(BDT-tPPD) showed s-type and linear curvature backbones. • P(BDT-tPPD) provided higher PCE in binary and ternary OSCs than P(BDT-fPPD). • The higher crystallinity of P(BDT-fPPD) provoked aggregation and offer low PCE. [ABSTRACT FROM AUTHOR]