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Quasi-layered all-polymer solar cells (QLA-PSCs) were fabricated based on wide bandgap polymer PM6 as a donor and narrow bandgap polymer PY-IT as an acceptor. A nonfullerene acceptor, L8-BO, is deliberately selected as a solid additive due to its similar chemical structure to the segment of polymer acceptor PY-IT. The power conversion efficiency (PCE) of the QLA-PSCs is increased from 16.14% to 17.74% by incorporating 2 wt% L8-BO into the PY-IT layer, benefiting from the synergistically increased short circuit current density (24.45 mA cm−2vs. 23.41 mA cm−2) and fill factor (76.38% vs. 72.60%). The contribution of L8-BO as a solid additive on the performance improvement of the QLA-PSCs can be summarized as follows: (i) it induces more ordered molecular orientation of PY-IT confirmed from GIWAXS; (ii) it enlarges the exciton diffusion length in the PY-IT layer and facilitates efficient hole transfer from PY-IT to PM6 as demonstrated by transient absorption; (iii) it increases the exciton dissociation interface as evidenced by the contact angle and photoluminescence of PM6/PY-IT without or with L8-BO. It should be highlighted that the 2000 h storage stability of the QLA-PSCs can be significantly improved, with PCE retention increasing from 85.1% to 90.2% of the initial value upon incorporating L8-BO as a solid additive. The effect of the universality of the nonfullerene acceptor as a solid additive on the performance improvement of QLA-PSCs can also be confirmed by the boosted PCE to 16.71% or 16.79% with Y6 or BO-4F as a solid additive. This work shows that a small molecular nonfullerene acceptor may induce a polymer acceptor molecular arrangement to further improve the performance of QLA-PSCs. [ABSTRACT FROM AUTHOR]

Broadband photomultiplication type all-polymer photodetectors (PM-APDs) are achieved on the basis of ITO/PFN-Br/PBDB-T : PYF-T-o (3 : 100, wt/wt)/LiF/Au as the configuration. Isolated hole traps are formed with PBDB-T encircled by PYF-T-o in the active layers. Trapped-holes in the vicinity of the Au electrode can cause interfacial band-bending to assist electron tunneling-injection into the active layers for achieving the PM phenomenon. The PM-APDs exhibit broad spectral response covering 310–900 nm, which is primarily dependent on the trapped-hole distribution in the vicinity of the Au electrode. The performance of PM-APDs could be improved by decreasing the active layer thickness, benefitting from the optimized electron tunneling-injection and collection. An ultrathin (∼1 nm) LiF layer is utilized as an interfacial layer to decrease electron injection barrier, leading to over one magnitude improvement of external-quantum-efficiency (EQE). The EQE of PM-APDs with the LiF layer could be increased to 18 000% at 360 nm and 9000% at 850 nm under 4 V applied bias, accompanied by the specific detectivity of 3.6 × 1012 Jones at 360 nm and 4.2 × 1012 Jones at 850 nm. The PM-APDs with the LiF layer are successfully applied in an optical pulse counting circuit, demonstrating the sensitive photodetection capability and feasibility in this practical application. [ABSTRACT FROM AUTHOR]

Wide bandgap polymer donor PM6 and narrow bandgap polymer acceptor PY-IT were selected to construct all-polymer solar cells (all-PSCs) with a layer-by-layer (LbL) or bulk heterojunction (BHJ) structure. The solvent additive 1-chloronaphthalene (CN) plays a vital role in improving the performance of all-PSCs. The power conversion efficiency (PCE) of LbL all-PSCs is improved to 15.81% from 13.67% by incorporating 1 vol% CN in PY-IT solution, benefiting from the simultaneously enhanced short circuit current density (JSC) of 22.61 mA cm−2 and fill factor (FF) of 73.62%. A similar phenomenon is also observed in BHJ all-PSCs whose PCE increased from 13.29% to 15.29% by incorporating 1 vol% CN in PM6:PY-IT blend solution, originating from the optimized phase separation for better exciton dissociation and charge transport in the BHJ active layers. Over 15% PCE improvement can be obtained in the BHJ and LbL all-PSCs by incorporating appropriate additive CN as a morphology regulator. It should be noticed that the PCEs of LbL all-PSCs with CN are higher than those of other all-PSCs, indicating that the LbL processing method combined with the additive should be a prospective strategy to fabricate highly efficient all-PSCs. [ABSTRACT FROM AUTHOR]

Photomultiplication-type organic photodetectors (PM-OPDs) have attracted enormous interest owing to their high sensitivity toward weak light and, especially, due to their excellent parasitic stability when using a single polymer as the active layer. Herein, three different polymers, DCP1-3, were synthesized with different amounts of PC61BM pendants as intramolecular traps, and they were successfully applied to high-stability PM-OPDs. Photogenerated electrons will be trapped by suspended PC61BM in the polymers to induce interfacial band-bending for hole tunneling injection, and the injected holes can be efficiently transported along the channels of the polymer under bias. The thickness of the ultrathin PFN–Br interfacial layer was optimized to decrease the dark current density. An EQE of 19100% at 365 nm was obtained for DCP3-based PM-OPDs using PFN–Br as the interfacial layer under a bias of 20 V. The optimized PM-OPDs exhibit excellent stability, with no photocurrent decay after 70 days of storage in a nitrogen-filled glove box, which is attributed to the locking of donor and acceptor segments through covalent links in the polymer. The optimized PM-OPDs can be employed to measure the heart rate (HR) of humans under different pulsatile conditions, indicating the promising application prospects of PM-OPDs with a single polymer as the active layer. [ABSTRACT FROM AUTHOR]

Layer-by-layer polymer solar cells (LbL-PSCs) were prepared with PNTB6-Cl as the donor and Y6 as the acceptor by a sequential spin-coating method. Two solvent additives DPE and DFB were individually incorporated into PNTB6-Cl chlorobenzene solution and Y6 chloroform solution. A PCE of 17.53% was achieved for the optimal LbL-PSCs with two solvent additives, which is much larger than the PCE of 16.38% for the LbL-PSCs without solvent additives. Over 7% PCE enhancement can be realized by individually employing solvent additives in donor and acceptor layers, resulting from the simultaneously enhanced open circuit voltage (VOC) of 0.88 V, short circuit current density (JSC) of 26.63 mA cm−2 and fill factor (FF) of 74.83%. The photogenerated exciton distribution, charge transport and collection in the LbL-PSCs can be optimized by employing different solvent additives in donor and acceptor solutions. Meanwhile, the efficient energy transfer from PNTB6-Cl to Y6 can provide an additional channel for improving the exciton utilization efficiency through exciton dissociation at PNTB6-Cl/Y6 interfaces. Meanwhile, the PCEs of LbL-PSCs are better than those of bulk heterojunction PSCs with the same materials and solvent additives, indicating the great potential of LbL-PSCs for commercial application. [ABSTRACT FROM AUTHOR]

Solution-processed organic photovoltaics (OPVs) have the superiorities of light weight, low cost, easy fabrication, high mechanical flexibility and good semitransparency, enabling great potential in next-generation photovoltaic technology. All-small-molecule OPVs (SMPVs) have great potential in commercial application thanks to the unique merits of small molecule materials with well-defined chemical structures and pre-eminent batch-to-batch replicability. With great efforts on material innovation and device engineering, SMPVs have achieved 17% power conversion efficiency (PCE), which still lags behind that of polymer based OPVs. It is significant to make a comprehensive summary on studies on SMPVs for further performance improvement. In this review, the development of SMPVs can be summarized as small molecular material design and device engineering. Challenges and perspectives on this field are put forward for developing high performance SMPVs. This summary on the typical studies on SMPVs would be instructive for researchers in synthesizing new small molecular materials and fabricating highly efficient SMPVs. [ABSTRACT FROM AUTHOR]

Photomultiplication organic photodetectors (PM-OPDs) were successfully constructed with a planar structure of PBDB-T/ITIC-Br as the active layer sandwiched by electrodes. Some isolated electron traps near the top surface of PBDB-T will be formed because small content ITIC-Br will permeate into PBDB-T layer prepared by sequential spin-coating method. The PM-OPDs achieve an external quantum efficiency (EQE) of 260% at 360 nm under a −9 V bias. The phosphorescent material FIrpic was incorporated into the PBDB-T layer to adjust the PBDB-T molecular arrangement for enhancing the hole mobility in the active layer. The optimal PM-OPDs with PBDB-T : FIrpic (100 : 10, wt/wt) display an EQE value of 2500% at 360 nm under a −9 V bias. A linear dynamic range (LDR) of 137 dB and a specific detectivity (D*) of 4.2 × 1012 Jones are also achieved in PM-OPDs with PBDB-T : FIrpic (100 : 10, wt/wt). Moreover, high-quality imaging with the PM-OPDs as photosensitive element was realized by utilizing imaging systems without current preamplifiers, indicating that the PM-OPDs have potential applications in imaging. [ABSTRACT FROM AUTHOR]

Over 200 nm thickness of active layers are essential for achieving efficient organic photovolatics (OPVs) using the roll-to-roll (R2R) large-scale production technology. In this study, a series of OPVs with 300 nm thick active layers were prepared with PM6:BTP-4F-12:BP-4F as active layers. The PM6:BTP-4F-12- and PM6:BP-4F-based binary OPVs achieve power conversion efficiencies (PCE) of 14.62% and 14.14%, respectively, with 300 nm thick active layers, also exhibiting complementary photovoltaic parameters. A PCE of 15.63% is achieved by the optimized ternary thick-film OPVs by combining the superiorities of two binary thick-film OPVs, deriving from a short circuit current density (JSC) of 26.57 mA cm−2, an open circuit voltage (VOC) of 0.840 V and a fill factor (FF) of 70.03%. The performance improvement of ternary thick-film OPVs should be mainly ascribed to the optimized molecular arrangement and phase separation for efficient charge transport in ternary thick active layers, which can be confirmed from the significantly improved FFs of ternary thick-film OPVs. This study indicates that the ternary strategy has great potential in preparing efficient thick-film OPVs. [ABSTRACT FROM AUTHOR]

UV-Vis-NIR broad-band organic photomultiplication-type photodetectors (OPMPDs) were fabricated with a device structure of indium tin oxide (ITO)/zinc oxide (ZnO)/(∼150 nm) active layers/Au. The active layers consisted of a 2,2′-((2Z,2′Z)-((12,13-bis(2-ethylhexyl)-3-undecyl-9-(undecyloxy)-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2′′,3′′:4′,5′]thieno[2′,3′:4,5]pyrrolo[3,2-g]thieno[3,2-b]indole-2,10-diyl)bis(methaneylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H,1-diylidene))dimalononitrile (Y6-1O):5-(5-(4,8-bis(4-chloro-5-(2-ethylhexyl)thiophen-2-yl)-6-methylbenzo[1,2-b:4,5-b′]dithiophen-2-yl)-4-(2-butyloctyl)-2-yl)-8-(4-(2-butyloctyl)-5-thiophen-2-yl)dithieno[3′,2′:3,4;2′′,3′′:5,6]benzo[1,2-c][1,2,5]thiadiazole (D18-Cl) (1.6 : 1, wt/wt) layer determining the spectral response range and one photomultiplication (PM) layer [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM):poly(3-hexylthiophene-2,5-diyl) (P3HT) (100 : 5, wt/wt). The spectral response of the double-layered OPMPDs was determined by the trapped-hole distribution in PC71BM:P3HT near by Au electrode, which mainly originated from the photogenerated hole in the Y6-1O:D18-Cl layer. The trapped-hole in P3HT induced interfacial band-bending for efficient electron-tunneling injection from the Au electrode. The trapped-hole-induced electron-tunneling injection could be markedly enhanced by increasing the applied voltage, leading to markedly improved external quantum efficiency (EQE) values. The double-layered OPMPDs exhibited a broad spectral response range from 300 to 1000 nm, and achieved a highly effective EQE of approximately 50 400% at 360 nm under an applied voltage of 5 V, which was the highest value among organic photodetectors (OPDs) under the same applied voltage. Moreover, the maximum specific detectivity (D*) of 3 × 1012 jones and a linear dynamic range (LDR) of 120 dB at 810 nm under an applied voltage of 5 V were achieved in the double-layered OPMPDs. This study brings forward a smart strategy to achieve high performance broad-band OPMPDs by employing double-layered thin active layers. [ABSTRACT FROM AUTHOR]

All-polymer photodetectors with photomultiplication were fabricated with PMBBDT and N2200 as photoactive layers, which exhibit an external quantum efficiency of 20   700% under 4 V. The signal-to-noise ratio, linear dynamic range and specific detectivity were simultaneously enhanced by empolying a PEDOT:PSS/P-TPD double hole transport layer. An optical switch system without any current amplifier was realized. [ABSTRACT FROM AUTHOR]

Semitransparent organic solar cells (OSCs) were fabricated with a broad bandgap polymer D18-Cl as the donor (D), narrow bandgap small molecule Y6-1O as the acceptor (A) and ultra-narrow bandgap material Y6 as the third component. A power conversion efficiency (PCE) of 14.92% can be obtained from opaque OSCs with D18-Cl:Y6-1O (1.1 : 1.6, wt/wt or 0.7 : 1.6, wt/wt) as active layers, which is due to the dependence of the three well-balanced photovoltaic parameters on D18-Cl content in the active layer. It should be highlighted that the average visible transmittance (AVT) of blend films can be markedly enhanced from 30.3% to 47.3% with decrease in D:A from 1.1 : 1.6 to 0.7 : 1.6 (wt/wt), which is highly conducive to the preparation of semitransparent OSCs. Keeping the D:A as constant (0.7 : 1.6, wt/wt), 16.05% PCE is achieved in opaque ternary OSCs with D18-Cl:Y6-1O:Y6 (0.7 : 0.8 : 0.8, wt/wt) as the active layers, resulting from the slightly increased JSC of 23.21 mA cm−2 and FF of 76.74%. The AVT of the corresponding ternary blend films is also improved to 50.1%. Semitransparent ternary OSCs are fabricated with Au (1 nm)/Ag (20 nm, 15 nm, 10 nm) replacing 100 nm Ag as the electrode. A PCE of 13.02%, an AVT of 20.2% and light utilization efficiency of 2.63% are obtained from the semitransparent OSCs with Au (1 nm)/Ag (10 nm) as the electrode. This work indicates that adjusting D:A weight ratio and employing a ternary strategy should have great potential in simultaneously improving the PCE and AVT of semitransparent OSCs, especially using a wide bandgap polymer as the donor. [ABSTRACT FROM AUTHOR]

A new zinc porphyrin, named as Por4IC, was synthesized, which through extension of conjugation and an enhancement of planarity and donor–acceptor interactions exhibits a very low band gap. The molecule was able to efficiently facilitate a photomultiplication effect in blend with P3HT which was assisted by electron trapping followed by hole tunneling injection from the Al electrode giving rise to a high external quantum efficiency of 22 182% and a specific detectivity of 4.4 × 1012 Jones at 355 nm and at −15 V bias. This work introduces porphyrin derivatives as promising dopants for photomultiplication type photodetectors. [ABSTRACT FROM AUTHOR]

Due to their unique merits, asymmetrical fused-ring electron acceptors (FREAs) have received increasing attention in the field of organic photovoltaics (OPVs). Herein, we designed and synthesized an asymmetrical FREA, namely AY6, by employing a cross-conceptual strategy which combines the structural features of asymmetrical IT6-4F with high-performance Y6. Compared to Y-shape Y6, X-shape AY6 shows poor crystallization properties and thus a significantly blue-shifted absorption. However, it is precisely because of this unfavorable self-stacking effect that AY6 has an opportunity to pack with PM6 and form a new intermixed phase. As a result, the PM6:AY6 blend film exhibits a perfect face-on orientation with stronger π–π stacking than the PM6:Y6 blend film, which facilitates efficient exciton dissociation and balanced carrier transport, and therefore higher FF. In general, such a cross-conceptual design strategy is an effective method which not only boosts the efficiency of asymmetrical FREA-based OSCs but also increases the fill factors of OSCs based on Y6-like FREAs. [ABSTRACT FROM AUTHOR]

Broadband organic photodetectors with photomultiplication (PM-OPDs) can be realized in the device structures of ITO/PEDOT:PSS/active layers/Al, where the active layers contain one broad bandgap polymer PDBD-T and a much lower amount of the ultra-narrow bandgap material, IEICO-4F. The active layers have an efficient single carrier (hole) transport property, leading to the low dark current of the PM-OPDs. The rather low amount of IEICO-4F surrounded by PBDB-T will become some isolated electron traps due to their differences in the lowest unoccupied molecular orbital levels. The photogenerated holes will be efficiently transported along the channels formed by PBDB-T, and the photogenerated electrons will prefer to be trapped in the isolated IEICO-4F. The trapped electrons in IEICO-4F near the Al electrode will induce interfacial band bending for the hole tunneling injection, achieving the photomultiplication phenomenon. The optimal PM-OPDs with PBDB-T : IEICO-4F (100 : 3, wt/wt) as active layers exhibited an external quantum efficiency (EQE) of >100% in the spectral range from 310 nm to 850 nm. The EQE of PM-OPDs can reach 1350% at 675 nm and 400% at 850 nm under −20 V bias. The ultra-narrow bandgap material IEICO-4F plays vital roles in realizing the PM phenomenon and extending the near infrared spectral response range. [ABSTRACT FROM AUTHOR]

Dual molecular engineering of alkyl side chains and halogen accepting ends of asymmetric fused-ring acceptors has been proposed for controlling aggregation for optimized organic solar cells (OSCs). Fluorination or chlorination on end-capped groups are explored along with linear octyl (C8) or branched 2-butyl-1-octyl chain (BO) substitution on the donating core. The inherent features of the larger Cl atom and longer C–Cl bond markedly extend the backbone stacking area and thus enhance molecular aggregation, while bulky BO chain exert a heavier steric shielding effect on backbone stacking. Consequently, IPTBO-4Cl shows properly weakened intermolecular interaction for balanced molecular aggregation. IPTBO-4Cl when blended with a PM6 polymer donor delivers a highest power conversion efficiency (PCE) of 15% and a 72.6% fill factor (FF). Expectedly, fluorinated IPT-4F bearing shorter C8 chains outputs a good PCE nearing 15% with a 74.2% FF. To the best of our knowledge, the PCE of 15% is by far the highest for asymmetric FRA based OSCs. By contrast, IPT-4Cl and IPTBO-4F with either excessively strong or weak aggregation result in relatively low photovoltaic performance. Our results demonstrate controlling aggregation via delicate molecular engineering is an undeniably effective way to achieve efficient OSCs. [ABSTRACT FROM AUTHOR]

Efficient ternary organic photovoltaics (OPVs) are fabricated with two polymer materials PF2 and J71 as donors and Y6 as the acceptor. The PF2 and J71 based binary OPVs exhibit 10.26% and 9.56% power conversion efficiency (PCE), respectively. Even with similar highest occupied molecular orbital (HOMO) energy levels of PF2 and J71, the J71 based binary OPVs show a relatively high open circuit voltage (VOC) of 0.86 V compared with 0.71 V for PF2 based binary OPVs. The VOCs of ternary OPVs monotonously increased with the increase of J71 content in donors, which should be mainly ascribed to the reduced energy loss according to the VOCs of two binary OPVs and the HOMO energy levels of two donors. The short circuit current density (JSC) and fill factor (FF) of ternary OPVs can also be simultaneously enhanced with the J71 content up to 30 wt% in donors, leading to 12.12% PCE of the optimized ternary OPVs with a JSC of 24.97 mA cm−2, a FF of 64.70% and a VOC of 0.75 V. Reducing energy loss by the ternary strategy is rarely reported in the literature, which should also be an efficient method to realize performance improvement of OPVs. [ABSTRACT FROM AUTHOR]

For acceptor–donor–acceptor (A–D–A) type non-fullerene small molecule acceptors (NF-SMAs), the electron-deficient active methylene end groups are pivotal for adjusting their properties and photovoltaic performances. However, a limited variety of end groups is not conducive to the full development of organic solar cells (OSCs) based on NF-SMAs. Herein, we developed a novel 9H-indeno[1,2-b]pyrazine-2,3-dicarbonitrile (IPC) end group and applied it into the design and synthesis of NF-SMAs called BTOIPC. BTOIPC with potential intramolecular C＝N⋯S interactions showed a planar conformation and small torsion angle. The strong electron-withdrawing ability of IPC endowed BTOIPC with a low optical bandgap (E optg of 1.45 eV) and suitable HOMO and LUMO energy levels, similar to those of BT-IC. OSCs based on PBDB-T:BTOIPC achieved a power conversion efficiency (PCE) of 9.31% with a fill factor (FF) close to 70% and an energy loss (Eloss) of 0.57 eV, which are comparable with those of the reported BT-IC. The advantageous features of the PBDB-T:BTOIPC bulk-heterojunction layer, such as high and balanced carrier mobility, good exciton dissociation, minor charge recombination and uniform morphology, contributed together to the good performance of IPC-based SMA. These results implied that IPC is a potential end group for NF-SMAs, and the modifiable structure of IPC gives IPC-based SMAs an ability to realize higher PCE in OSCs. [ABSTRACT FROM AUTHOR]

All-polymer photodetectors (all-PPDs) are successfully fabricated with two polymers P3HT and PZ1 as active layers. The weight ratio of P3HT to PZ1 and the self-assembly time of the active layers were step-by-step optimized to improve the performance of the all-PPDs. The photomultiplication (PM) phenomenon is achieved in the all-PPDs with an external quantum efficiency (EQE) over 100% in the whole response range. The EQE values of the optimized PM type all-PPDs can be greatly improved with a bias increase. The EQE values are increased to 46 700% at 375 nm and 31 700% at 615 nm under a −20 V bias. The working mechanism of the PM type all-PPDs is hole tunneling injection from an external circuit assisted by interfacial trapped photogenerated electrons in P3HT/PZ1/P3HT. The specific detectivity (D*) values are improved to 5.6 × 1012 Jones at 375 nm and 6.1 × 1012 Jones at 615 nm under a −20 V bias. The relatively large D* can be attributed to the enhanced hole tunneling injection under light illumination conditions and the relatively low dark current density. [ABSTRACT FROM AUTHOR]

The power conversion efficiency (PCE) of 13.00% was achieved in PBDB-T:Y16-based polymer solar cells (PSCs). On this basis, PCE of ternary PSCs was improved to 14.11% by incorporating 15 wt% MeIC1 in acceptors, resulting from simultaneously enhanced short circuit current (JSC) of 22.76 mA cm−2 and fill factor (FF) of 68.22%. The observed 14.11% PCE is among the highest values for all ternary PSCs. Y16 and MeIC1 preferred to form an alloyed acceptor due to good compatibility, which is beneficial to the formation of efficient electron transport channels in ternary active layers. Photon harvesting, exciton dissociation and charge transport could be synergistically optimized by incorporating 15 wt% MeIC1 in the acceptors. The optical field and photogenerated exciton distribution in active layers were calculated according to their intrinsic properties, which could provide more intuitive evidence of JSC and FF improvement. The photogenerated exciton distribution in active layers could also be optimized by employing a ternary strategy, which was beneficial for better balance charge collection efficiency and for achieving high FF of the ternary PSCs. This work further demonstrates that ternary strategies have great potential for improving the PSC performance by simultaneously optimizing photon harvesting and photogenerated exciton distribution in active layers. [ABSTRACT FROM AUTHOR]

Opaque and semitransparent polymer solar cells (PSCs) were prepared with the narrow band gap donor PTB7-Th and the ultra-narrow band gap acceptor IEICO-4F by optimizing their doping ratios. The power conversion efficiency (PCE) of opaque PSCs can be maintained at over 11% by altering PTB7-Th : IEICO-4F ratios from 1.4 : 1.5 to 0.8 : 1.5 (wt/wt), along with a red-shifted absorption edge of active layers. The red-shifted absorption edge should be attributed to IEICO-4F molecular aggregation due to the relatively increased IEICO-4F content in active layers. The increased photon harvesting in the near infrared light range due to IEICO-4F molecular aggregation and decreased photon harvesting in the visible light range with lower PTB7-Th content provide great potential to prepare efficient semitransparent PSCs. The semitransparent PSCs were prepared with 1 nm Au/11 nm Ag replacing 100 nm Al as the electrode. The average visible transmittance (AVT) of semitransparent PSCs is increased from 23.7% to 27.1% by decreasing the PTB7-Th content in active layers, along with a slight PCE decrease from 9.48% to 9.06% and a lower cost. The optimized 9.06% PCE and 27.1% AVT should be impressive values for semitransparent PSCs. This work may provide a smart strategy to achieve efficient semitransparent PSCs with low cost by decreasing the narrow band gap donor content in active layers. [ABSTRACT FROM AUTHOR]

Solution processed interfacial layers are commonly employed in bulk heterojunction organic solar cells (OSCs) for better charge collection. PDIN interfacial layers were prepared by employing a static or dynamic spin coating method from PDIN methanol solution, and defined as the S-PDIN or D-PDIN layer. The OSCs with a S-PDIN layer exhibit 13.88% power conversion efficiency (PCE) with a virtual high short circuit density (JSC) of 26.45 mA cm−2 and relatively low fill factor (FF) of 58.94% during the current density versus voltage (J–V) measurement without a shadow mask. 12.56% PCE is achieved for OSCs with a D-PDIN layer, along with a JSC of 18.85 mA cm−2 and FF of 74.88%. Over 77% FFs are obtained for OSCs with a S-PDIN or D-PDIN layer during J–V measurement with a shadow mask, and both OSCs exhibit a very similar JSC and PCE. The virtual high JSCs and relatively low FF of OSCs with a S-PDIN layer may be due to the enhanced conductivity of PEDOT:PSS during preparation of the PDIN layer by the SSC method, which can be further confirmed from the OSCs with a methanol treated PEDOT:PSS layer. This work indicates that a well-balanced JSC and FF should be an important evaluating indicator for efficient OSCs, and an appropriate shadow mask is necessary to measure the J–V curves of OSCs with a solution processed interfacial layer. [ABSTRACT FROM AUTHOR]

Perovskite photodetectors (PPDs), which combine the advantages of perovskite semiconductor materials with superior optical and electronic properties and solution-processed manufacturing, have emerged as a new class of revolutionary optoelectronic devices with potential for various practical applications. Encouraged by the development of various solution-synthesis and film-deposition techniques for controlling the morphology and composition of perovskite materials with interesting optoelectronic properties, increasing research attention is focused on the development of high performance PPDs. In this review, the recent progress on emerging PPDs is comprehensively summarized from the perspective of device physics and materials science. The strategies for extending the spectral response range of PPDs and improving the performance of devices are investigated. Furthermore, the methods for realizing narrowband photodetectors are also discussed, where filter-free and self-filter narrowband PPDs are achieved based on the concept of charge collection narrowing. Meanwhile, the promising future directions in this research field are proposed and discussed, including multifunctional PPDs, perovskite–organic hybrid photodetectors, flexible and transparent PPDs, self-powered PPDs, and photodetector systems and arrays. This review provides valuable insights into the current status of highly sensitive PPDs and will spur the design of new structures and devices to further enhance their photo-detection performances and meet the need of versatility in practical application. [ABSTRACT FROM AUTHOR]

One narrow bandgap donor (PTB7-Th) and two ultra-narrow bandgap acceptors (COi8DFIC and IEICO-4F) were elaborately selected to fabricate semitransparent ternary polymer solar cells (PSCs). To find out the optimal content of IEICO-4F in the acceptors, a series of opaque PSCs were first fabricated with 100 nm of Ag as the electrode. The power conversion efficiency (PCE) of the optimized opaque ternary PSCs arrived at 11.94% by incorporating 15 wt% IEICO-4F in the acceptors. Then, the thickness of Ag was adjusted to balance its electrical conductivity and transmittance, and the 100 nm of Ag was replaced by 15 nm of Ag as a semitransparent electrode. The semitransparent electrode possesses high transmittance in the visible light range and low transmittance in the long wavelength range, which is propitious for photon harvesting of ternary active layers with two ultra-narrow bandgap acceptors. The optimized semitransparent ternary PSCs show a synchronously improved PCE of 8.23% and an average visible transmittance (from 370 nm to 740 nm) of 20.78% compared with COi8DFIC based semitransparent binary PSCs. This work suggests the potential of a ternary strategy for fabricating highly efficient semitransparent PSCs with narrow or ultra-narrow bandgap materials as active layers. [ABSTRACT FROM AUTHOR]

Ternary non-fullerene polymer solar cells (PSCs) were fabricated with J71 as a donor and mixed ITIC:MeIC2 as acceptors. The power conversion efficiency (PCE) of the ternary PSCs reaches 11.6% for 20 wt% MeIC2 in the acceptors, which is larger than the 10.7% or 10.2% for binary PSCs with ITIC or MeIC2 as an acceptor. The PCE improvement of ternary PSCs is mainly attributed to the simultaneously enhanced short circuit current density (JSC) of 18.1 mA cm−2 and fill factor (FF) of 70.5%. The photon harvesting of ternary active layers can be optimized by adjusting MeIC2 content due to the complementary asborption of ITIC and MeIC2, leading to the enhanced JSC. Meanwhile, phase separation of ternary active layers can be further optimized for efficient exciton dissociation and more balanced charge transport. The improved FF can be well explained from the more balanced charge transport evaluated by the ratios of hole mobility to electron mobility in the active layers. [ABSTRACT FROM AUTHOR]

Two new non-fullerene (NF) acceptors, namely BDTIT-M and BDTThIT-M, were rationally designed to optimize the energy levels and optical bandgap. BDTIT-M is derived by changing the end-group of NFBDT into slightly weak DCI-M, and BDTThIT-M is obtained by adding two conjugated thiophene side-chains into a ladder-type core of BDTIT-M. By incorporating with the polymer donor PBDB-T, BDTIT-M based organic solar cells (OSCs) deliver a higher PCE of 11.31% compared to that of NFBDT based cells, which is mainly attributed to the increased VOC and FF. A higher PCE of 12.12% with a small energy loss of ∼0.588 eV is achieved compared with BDTThIT-M based OSCs, benefiting from the elevated LUMO level, narrowed bandgap, and enhanced absorption coefficient and electron mobility of BDTThIT-M compared with BDTIT-M. The combination of a methyl-modified end-group and conjugated side-chain should be an efficient strategy to elevate the LUMO and HOMO levels with different amplitudes for realizing simultaneous improvement in VOC and JSC. [ABSTRACT FROM AUTHOR]

In this work, we present a structurally defined blue-shift non-fullerene electron acceptor (ITCT) matching with PTB7-Th as the electron donor for high-performance fullerene-free polymer solar cells (PSCs). The PTB7-Th/ITCT blend based bulk-heterojunction (BHJ) devices give an appreciable PCE of 8.23% and a relatively high VOC of 0.96 V without any optimization. Upon device processing with thermal annealing and the addition of 0.1% DIO additive, the active layer achieves a more ordered and crystalline morphology. Consequently, a high PCE of 10.42% has been achieved with a VOC of 0.95 V, a JSC of 15.13 mA cm−2 and a high FF of 0.72. To the best of our knowledge, the PCE of 10.42% is among the highest values reported in the literature to date for non-fullerene PSCs using PTB7-Th as the electron donor. [ABSTRACT FROM AUTHOR]

A new small molecule-based hole selective material (HSM), 4,4′,4′′-(7,7′,7′′-(5,5,10,10,15,15-hexahexyl-10,15-dihydro-5H-diindeno[1,2-a:1′,2′-c]fluorene-2,7,12-triyl)tris(2,3-dihydrothieno[3,4-b][1,4]dioxine-7,5-diyl))tris(N,N-bis(4-methoxyphenyl)aniline) (TRUX-E-T), has been developed by a facile synthesis with reduced cost. The highest occupied molecular orbital energy level and lowest unoccupied molecular orbital energy level of TRUX-E-T are −5.10 and −2.50 eV, respectively, making it a suitable HSM for lead iodide perovskite solar cells. TRUX-E-T can be smoothly deposited onto perovskite layers, enabling efficient perovskite solar cells with thin TRUX-E-T layers (∼50 nm), which helps cut the unit cost of the HSL used in PVSCs to approximately one-fortieth (1/40) of 2,2′,7,7′-tetrakis (N,N-di-p-methoxyphenylamino)-9,9′-spirobifluorene (spiro-OMeTAD). Additionally, TRUX-E-T exhibits hole mobilities as high as 2.47 × 10−4 cm2 V−1 s−1, better than spiro-OMeTAD. As a result, our perovskite solar cells using TRUX-E-T have shown high fill factors up to 82%. The champion cell achieved a maximum power conversion efficiency of 18.35% (16.44%) when measured under reverse (forward) voltage scan under AM1.5 G 100 mW cm−2 illumination. Our un-encapsulated cells exhibited good stability in ambient air, maintaining 96.4% of their initial efficiency of 18.35% after 20 days of storage. [ABSTRACT FROM AUTHOR]

Herein, a liquid crystal material, BTR, was elaborately selected as the third component to complement PTB7-Th for the fabrication of highly efficient ternary polymer solar cells (PSCs). Via incorporating 10 wt% BTR in their donors, the champion power conversion efficiency (PCE) of the PSCs increased from 10.08% to 10.83%, resulting from the enhanced short circuit current (JSC) of 19.23 mA cm−2 and fill factor (FF) of 72.21%. The small amount of incorporated BTR may prefer to distribute in the PTB7-Th networks and has good miscibility with PC71BM. The excitons on BTR may dissociate into free charge carriers at the BTR/PC71BM interfaces and also transfer their energy to PTB7-Th through Förster resonance energy transfer, resulting in improved exciton utilization. Moreover, the molecular arrangement and morphology of the active layers could be optimized by incorporating appropriate amount of BTR as a nucleating agent, also leading to enhanced stability of the ternary PSCs. The positive effects of BTR on the performance improvement of PSCs were confirmed from the inverted and conventional structures of the cells. [ABSTRACT FROM AUTHOR]

It is a great challenge to obtain narrowband and photomultiplication (PM) type organic photodetectors (OPDs) without optical filters due to the broad absorption range and large exciton binding energy of organic materials. Narrowband OPDs with the special structure of ITO/PFN-OX/P3HT : PC61BM (100 : 1,wt/wt)/Al were successfully fabricated with different active layer thicknesses, exhibiting a tunable response window and PM phenomenon under bi-directional bias. The OPDs exhibit U-shaped EQE spectra with two narrowband response windows under forward bias and a single narrowband response window under reverse bias. The best EQE of the optimized OPDs with a 4.0 μm thick active layer approaches 7160% or 8180% for 340 nm or 650 nm light illumination at 60 V and 1640% for 665 nm light illumination at −60 V, respectively. The most important features of the optimized OPDs is that the full width at half-maximum (FWHM) of their response windows is less than 30 nm under bi-directional biases, which can be well maintained at large bias. The PM type narrowband OPDs working at bi-directional bias are the first to be reported with a tunable response range, further indicating that the density of the electrons trapped in PC61BM near the hole injection electrode plays the key role in determining the interfacial band bending for hole tunneling injection from the external circuit. [ABSTRACT FROM AUTHOR]

Solution-processed small molecule solar cells (SMSCs) are fabricated based on DRCN5T:PC71BM as active layers, the power conversion efficiency (PCE) is markedly increased from 3.63% to 9.11% for the active layers undergoing up-side-down thermal annealing and solvent vapor annealing post-treatments. The PCE improvement should be attributed to the appropriate phase separation consisting of enhanced crystallinity of donor and purified acceptor domain at nanoscale. The nematic liquid crystal small molecule BTR is selected as the second donor and morphology regulator to prepare ternary SMSCs. The champion PCE of ternary SMSCs was improved to 10.05% by mixing 1.5 wt% BTR, which corresponds to a 10.3% PCE improvement compared with the optimized binary SMSCs. The performance improvement is mainly attributed to the further optimized phase separation and complementary photon harvesting between DRCN5T and BTR, which could be well demonstrated from absorption spectra, two dimensional grazing incidence X-ray diffraction (2D-GIXD) and transmission electron microscopy (TEM). [ABSTRACT FROM AUTHOR]

The dynamic drying process of the active layer should play a vitally important role in determining the performance of polymer solar cells (PSCs). Donor molecular packing and acceptor redistribution can be optimized by two successive post-treatments on the active layer. The blend films were freshly prepared by spin-coating method and then immediately transferred to a covered glass Petri dish to allow self-assembly of the donor molecules. The films were then treated with methanol or PFN–methanol solution to adjust the acceptor redistribution. In this study, power conversion efficiencies (PCEs) of PSCs with PffBT4T-2OD:PC71BM as the active layer were improved from 6.74% to 8.75% by employing 80 min for self-assembly and 20 s of methanol soaking. The PCE was improved even further to 9.72% by inserting a PFN interfacial layer. The performance improvement was mainly attributed to the optimized PffBT4T-2OD molecular packing during the self-assembly process, ideal vertical phase separation driven by methanol soaking and efficient charge collection by insertion of a PFN interfacial layer. The molecular packing and vertical phase separation were characterized by grazing incidence X-ray diffraction (GIXD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), respectively. The experimental results solidly supported the effectiveness of the step-by-step optimization strategy. [ABSTRACT FROM AUTHOR]

Photon harvesting and phase separation can be synergistically optimized by using ternary strategy with appropriate DIB-SQ-doped Si-PCPDTBT:PC71BM as active layer. The power conversion efficiency (PCE) of ternary organic photovoltaic cells (OPVs) exhibits an increasing and then decreasing trend dependent on the increase in DIB-SQ doping ratio. The PCE of OPVs was increased from 5.52% to 6.18% by doping 3 wt% DIB-SQ while keeping the donor/acceptor doping weight ratio at 1 : 1.5. The PCE improvement can be attributed to the better trade-off between photon harvesting and phase separation in the ternary active layers. The degree of phase separation strongly influences energy or charge transfer between donors and charge transport in the ternary active layers. The dynamic process between donors was investigated according to J–V curves of cells without acceptor under light illumination. Experimental results fully confirm that this ternary strategy should have a brilliant future due to about 12% PCE improvement compared with Si-PCPDTBT:PC71BM-based binary OPVs. [ABSTRACT FROM AUTHOR]

A series of solvent additive-free polymer solar cells (PSCs) were fabricated with PBDT-TS1 : PC71BM (1 : 2, wt/wt) as the active layers; the performance of the PSCs can be enhanced by using MeOH:CH2Cl2 or MeOH:CB mixed solvent spin-coating treatment on the active layers. The maximum power conversion efficiency (PCE) of PSCs was increased from 6.69% to 7.21% or 7.76% by spin-coating the mixed solvents onto the active layers, respectively. The PCE improvement may be attributed to the increase in PC71BM elevated toward the top surface of the active layers during the mixed solvent spin-coating treatment. The redistribution of PC71BM in the active layers could also be indirectly confirmed from the variation of photoluminescence spectra and water contact angles of the corresponding films, as well as the J–V curves of electron-only devices. [ABSTRACT FROM AUTHOR]

Four isostructural donor–acceptor alternating polymers of benzodithiophene (BDT)/naphthodifuran (NDF) and benzoselenadiazole (BSe)/benzothiadiazole (BT) have been developed and evaluated for organic photovoltaics. The substitution of one-atom (Se for S) in the accepting units exerts remarkable impact on the optoelectronic properties of polymers. Extended absorption, narrowed bandgap and higher HOMO energy levels were observed for Se-containing polymers in comparison to their S-containing counterparts. Theoretical calculations confirmed the measurable effect on energy levels as found in experimental studies. Bulk-heterojuction solar cells based on the BDT–BSe copolymer and [6,6]-phenyl-C71-butyric acid methyl ester (1 : 2, w/w) blend films deliver the best PCE of 5.40%. BSe-based polymers showed enhanced photovoltaic performances than BT-based polymers. The device performance is found to be strongly dependent on the processing conditions and morphology of the active layers. [ABSTRACT FROM AUTHOR]

A series of ternary polymer solar cells (PSCs) were fabricated based on two narrow bandgap polymers PTB7 and PBDT-TS1 as the donors and PC71BM as the acceptor. The performances of the ternary PSCs monotonically increased along with the PBDT-TS1 doping ratio, up to 80 wt% in the donors. The optimum power conversion efficiency (PCE) achieved for the ternary PSCs was 7.91% with an open circuit voltage (VOC) of 0.76 V, a short circuit current density (JSC) of 18.85 mA cm−2 and a fill factor (FF) of 55.2% for the active layers with an 80 wt% PBDT-TS1 doping ratio in the donors. The optimized ternary PSCs show a 12.8% improvement compared to the optimum PCE of 7.01% for the binary PSCs with PBDT-TS1 as the donor and a 28.2% improvement compared with the optimum PCE of 6.17% for the binary PSCs with PTB7 as the donor. The FFs of all the ternary PSCs are larger than 54%, indicating efficient charge carrier transport channels in the ternary active layers. The energy or charge transfer between PTB7 and PBDT-TS1 should be neglected according to the investigation of the photoluminescence spectra of the blend films and the current density–voltage (J–V) curves of devices without the acceptor in the active layers. The ternary PSCs should be parallel-linkage structures with the donors independently working with the acceptor, which may be the most promising strategy for obtaining highly efficient ternary PSCs. [ABSTRACT FROM AUTHOR]

We report polymer photodetectors (PPDs) with an evident photomultiplication (PM) phenomenon, based on a sandwich structure ITO/PEDOT:PSS/P3HT:PC71BM(100:1)/Al. A similar device structure has been reported in our previous work, showing great potential as a new type of high performance PPD. However, we found more interesting new phenomena from these PPDs. Solid evidence is provided to prove the existence of photogenerated electron transport in the almost hole-only active layer under an applied bias. The transport of photogenerated electrons leads to electron accumulation near the Al electrode and the electron redistribution, which strongly affect the EQE spectral shape and the transient response of the PPDs. Our conclusion is further confirmed by confirmatory devices with a structure of Al(1)/P3HT:PC71BM(100:1)/Al(2). EQE spectra and transient Jph curves of the confirmatory devices accord well with our speculation. This discovery may provide a new insight to increase the response speed of PM type PPDs by adjusting the photogenerated electron distribution in the active layer. Considering that the PM type PPDs have much higher EQE than the traditional organic photodetectors, the improvement may further extend its potential applications with low cost. [ABSTRACT FROM AUTHOR]