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In this work, layer-by-layer organic photovoltaics (LbL OPVs) were prepared by sequentially spin-coating PM1 and L8-BO solutions. The solvent additive 1,8-diiodooctane (DIO), which has a high boiling point, and solid additive l,3,5-trichlorobenzene (TCB), which has a high volatile, were deliberately selected to incorporate with the L8-BO solutions. The power conversion efficiency (PCE) of LbL OPVs was considerably enhanced from 17.43% to 18.50% by employing TCB as the additive, profiting by the concurrently increased short-circuit current density (JSC) of 26.74 mA cm−2 and a fill factor (FF) of 76.88%. The increased JSCs of LbL OPVs with TCB as additive were ascribed to the tilted-up absorption edge in the long wavelength range and the external quantum-efficiency spectral difference between LbL OPVs with and without TCB as an additive. The molecular arrangement of L8-BO and the PM1 domain was enhanced with TCB as an additive, which was most likely responsible for the increased charge mobilities in the layered films processed with additives. It was indicated that the dynamic film-forming process of the acceptor layers plays a vital role in achieving efficient LbL OPVs by employing additive strategy. Over 6% PCE improvement of the LbL OPVs with PM1/L8-BO as the active layers can be achieved by employing TCB as additive. [ABSTRACT FROM AUTHOR]

Two kinds of polymer solar cells (PSCs) were fabricated with polymer donor PM6 and small molecule non‐fullerene acceptor L8‐BO as accepted based on bulk heterojunction (BHJ) or layer‐by‐layer (LbL) structure. The power conversion efficiency (PCE) of 18.43 % and 17.84 % can be achieved from the PSCs based on BHJ and LbL structure, respectively. Two kinds of PSCs exhibit the same open circuit voltage (VOC) of 0.88 V, which can be well explained from the same donor and acceptor materials and the same electrodes. The LbL based PSCs exhibit a relatively large short circuit current density (JSC) of 26.97 mA cm−2 and fill factor (FF) of 77.64 % in comparison with JSC of 26.64 mA cm−2 and FF of 76.07 % for BHJ based PSCs. The relatively high PCE of LbL based PSCs should be attributed to the sufficient exciton dissociation and charge collection efficiency, as well as the more balanced charge transport, which can be confirmed from the photogenerated current density dependence on the effective bias. This work demonstrates that layer‐by‐layer structure may have great potential in preparing highly efficient PSCs. [ABSTRACT FROM AUTHOR]

Donor PM6 and acceptor L8‐BO are employed to build semitransparent organic photovoltaics (ST‐OPVs). Opaque OPVs are fabricated by tuning the spin‐coating speed of PM6:L8‐BO solution to optimize the photon utilization by balancing photon harvesting and photogenerated carrier collection. The optimal opaque OPVs exhibit relatively high fill‐factor (FF) of 77.58% and power conversion efficiency (PCE) of 15.07%, the average visible transmittance (AVT) of corresponding PM6:L8‐BO films arrives to 53.25%, indicating great potential in realizing efficient ST‐OPVs. ST‐OPVs are built with 1 nm Au/(10, 15, 20, 25 nm) Ag as cathode, exhibiting the PCE/AVT of 11.53%/22.57%, 13.20%/14.24%, 14.28%/9.34%, and 14.71%/6.77%, respectively. Colorful ST‐OPVs are achieved by coupling different Ag/LiF/Ag Fabry‐Pérot (F‐P) resonator microcavity. Green ST‐OPVs with varied color coordinates are achieved by fixing LiF layer thickness as 110 nm and varying Ag layers′ thickness, originating from the adjusted transmittance spectra of green ST‐OPVs. Upon fixing Ag layers′ thickness as 15/25 nm and varying LiF layer thickness as 90, 110, and 145 nm, ST‐OPVs present colors of blue, green, and red with corresponding transmittance peak at 474, 553, and 657 nm. The corresponding PCE/peak transmittance (Tpeak) values arrive to 13.80%/37.8%, 13.31%/28.4%, and 13.20%/27.7%, which should be the best performance among reported colorful ST‐OPVs. [ABSTRACT FROM AUTHOR]

Series of bulk heterojunction (BHJ) and layer‐by‐layer (LbL) all‐polymer solar cells (APSCs) were prepared with polymer PM6 as donor and polymer PY‐DT as acceptor based on conventional and inverted configuration. Benefiting from the sequential deposition strategy, the good vertical phase separation and more ordered molecular arrangement can be formed in the LbL APSCs. The conventional LbL APSCs exhibit an optimized power conversion efficiency (PCE) of 17.24% with a relatively large short circuit current density of 23.83 mA cm−2 and fill factor of 74.60%, photogenerated excitons near the indium tin oxide electrode can be efficiently utilized through energy transfer from PM6 to PY‐DT and the self‐absorption effect of PM6 for its long exciton diffuse distance. The 17.24% PCE of conventional LbL APSCs is higher than 16.72% of conventional BHJ APSCs, 14.59% of inverted BHJ APSCs and 12.41% of inverted LbL APSCs. The rather low PCE of 12.41% for the inverted LbL APSCs further indicates that the energy transfer from donor to acceptor and self‐absorption effect of donor should play a vital role in determining the performance of LbL APSCs. This work provides more insights on the exciton and carrier dynamic process in sequentially deposited active layer, providing more guidance for preparing efficient LbL APSCs. [ABSTRACT FROM AUTHOR]

The power conversion efficiencies (PCEs) of organic photovoltaics (OPVs) have reached more than 19%, along with the prosperous development of materials and device engineering. It is meaningful to make a comprehensive review of the research of OPVs for further performance improvement. In this review, some typical materials of high-performance OPVs are summarized, including representative polymer donor materials, non-fullerene acceptor materials, and interfacial modification materials, as well as their design rules for molecular engineering. From the point of view of device engineering, active layer treatment and deposition technology are introduced, which can play a critical role in adjusting the degree of molecular aggregation and vertical distribution. Meanwhile, a ternary strategy has been confirmed as an efficient method for improving the performance of OPVs, and the multiple roles of the appropriate third component in the photo-electronic conversion process are emphasized and analyzed. The challenges and perspectives concerning this region are also put forward for further developing high-performance OPVs. [ABSTRACT FROM AUTHOR]

Organic semiconducting materials with fluorine or chlorine substitution are commonly designed to prepare efficient polymer solar cells (PSCs) through finely modulating the energy levels and absorption spectra. Herein, two small molecular acceptors with fluorine substitution L8‐BO or chlorine substitution eC9‐2Cl are selected to prepare ternary PSCs with PM6 as polymer donor. The optimal ternary PSCs exhibit a power conversion efficiency of 18.66%, benefiting from the simultaneously increased open‐circuit voltage (VOC) of 0.89 V, short‐circuit current density (JSC) of 26.63 mA cm−2, and fill factor of 78.74% when the content of chlorine substitution eC9‐2Cl is about 20 wt% in acceptors. Fluorinated and chlorinated substitutions can improve the VOC or JSC of the corresponding binary PSCs, which can be recombined into efficient ternary PSCs through optimizing their content in acceptors. Chlorinated materials have special crystalline conditions due to the specific features of the chlorine atoms with large atomic radius and the empty 3d orbits compared to the corresponding fluorinated materials. Adding an appropriate amount of the chlorine substitution eC9‐2Cl further enhances the crystallization and intermolecular interaction of the ternary PSCs, which is beneficial for charge transport in the active layer and for device performance improvement. [ABSTRACT FROM AUTHOR]

Layer‐by‐layer organic photovoltaics (LbL‐OPVs) are fabricated using wide bandgap polymer D18 with narrow photon harvesting range in visible light region and narrow bandgap small molecular N3 with strong near‐infrared photon harvesting; the only difference is D18 layer thickness adjusted by spin coating speed. A 15.75% power conversion efficiency (PCE) is obtained from the LbL‐OPVs with D18 layer prepared under 7000 round per minute of spin coating condition; the corresponding D18/N3 layers have a 52.06% of average visible transmittance (AVT) in the spectral range from 370 to 740 nm. Based on the optimized D18/N3 layers, semitransparent LbL‐OPVs are built with 1 nm Au/(10, 15, 20 nm) Ag as the top electrode. The PCE and AVT of semitransparent LbL‐OPVs can be simultaneously adjusted by altering Ag layer thickness due to its variable reflectance and conductivity of top electrode dependence on Ag layer thickness. The PCE/AVT of 12.58%/22.81%, 13.80%/15.09%, and 14.85%/9.48% can be individually achieved from the semitransparent LbL‐OPVs with 10, 15, or 20 nm‐thick Ag layer, which should be among the highest values of semitransparent OPVs based on bulk heterojunction or LbL structures. Adjusting donor layer thickness may be an effective method to construct efficient semitransparent LbL‐OPVs. [ABSTRACT FROM AUTHOR]

A series of binary and ternary polymer solar cells (PSCs) is successfully fabricated. The optimal ternary PSCs achieve a power conversion efficiency (PCE) of 18.14%, benefiting from the increased short circuit current density (JSC) of 26.53 mA cm−2 and fill factor (FF) of 78.51% in comparison with the JSCs (25.05 mA cm−2 and 25.65 mA cm−2) and the FFs (77.13% and 76.55%) of the corresponding binary PSCs. The photon harvesting ability of ternary active layers can be enhanced, which can be confirmed from the EQE spectral difference of the optimized ternary and binary PSCs, especially in the wavelength range from 680 nm to 800 nm. The refractive index and extinction coefficients of binary and ternary blend films are measured, which can well support the enhanced photon harvesting ability in different wavelength ranges. Photogenerated exciton distribution in active layers is simulated by the transmission matrix method based on the Beer–Lambert law. The photogenerated exciton density can be enhanced in the middle of the active layers by incorporating a third component in acceptors, which is conducive to charge collection by individual electrodes, resulting in the simultaneously enhanced JSC and FF of the optimal ternary PSCs. [ABSTRACT FROM AUTHOR]

Wide bandgap polymer D18 with narrow photon harvesting in visible light range and small molecule N3 with near‐infrared photon harvesting are adopted for building semitransparent organic photovoltaics (OPVs). To find out the optimal D18:N3 weight ratio for semitransparent OPVs, series of opaque OPVs are built with a varied D18:N3 weight ratio. The power conversion efficiency (PCE) and fill factor can be maintained over 16% and 77% in the D18:N3 (0.7:1.6, wt/wt) based opaque OPVs, respectively. The average visible transmittance (AVT) of the corresponding blend films can be achieved over 50%, demonstrating the great potential in fabricating efficient semitransparent OPVs. The semitransparent OPVs based on D18:N3 (0.7:1.6, wt/wt) are fabricated by using 1 nm Au/(10, 15, 20 nm) Ag as cathode. The thickness of Ag layers is varied to balance the optical properties and electrical properties of semitransparent top electrode. The semitransparent OPVs with 10 nm Ag achieve the highest light utilization efficiency of 2.90% with a PCE of 12.91% and an AVT of 22.49%, which should be among the best performance of reported semitransparent OPVs. This work demonstrates that the wide bandgap polymer donor with narrow photon harvesting in visible light range has great potential in preparing efficient semitransparent OPVs. [ABSTRACT FROM AUTHOR]

Efficient ternary blend organic photovoltaic devices (OPVs) are built based on a D18‐Cl:Y6 host system and star polymer donor PM6 as the third component. A power conversion efficiency (PCE) of 16.89% is achieved in D18‐Cl:Y6 host binary OPVs, with a short‐circuit current density (JSC) of 25.31 mA cm−2, an open‐circuit voltage (VOC) of 0.878 V, and a fill factor (FF) of 75.81%. Upon incorporating appropriate PM6 in active layers, the PCE of optimal ternary blend OPVs can be increased to 17.61%, benefiting from a JSC of 26.35 mA cm−2, a VOC of 0.871 V, and an FF of 76.82%. Polymers D18‐Cl and PM6 have good compatibility and similar highest occupied molecular orbital (HOMO) levels, which enable to form D18‐Cl:PM6 alloyed states for efficient hole transport in ternary blend active layers. Meanwhile, trap density in ternary blend active layers is decreased by incorporating PM6, which is conducive to weaken charge recombination in ternary blend active layers. The gradually varied VOC values of ternary blend OPVs can be well explained from the varied HOMO levels of D18‐Cl:PM6 alloyed states. The results indicate that two compatible polymer donors with similar HOMO levels have great potential in achieving efficient ternary blend OPVs. [ABSTRACT FROM AUTHOR]

A series of ternary organic photovoltaics (OPVs) are fabricated with one wide bandgap polymer D18-Cl as donor, and well compatible Y6 and Y6-1O as acceptor. The open-circuit-voltage (VOC) of ternary OPVs is monotonously increased along with the incorporation of Y6-1O, indicating that the alloy state should be formed between Y6 and Y6-1O due to their excellent compatibility. The energy loss can be minimized by incorporating Y6-1O, leading to the VOC improvement of ternary OPVs. By finely adjusting the Y6-1O content, a power conversion efficiency of 17.91% is achieved in the optimal ternary OPVs with 30 wt% Y6-1O in acceptors, resulting from synchronously improved short-circuit-current density (JSC) of 25.87 mA cm−2, fill factor (FF) of 76.92% and VOC of 0.900 V in comparison with those of D18-Cl : Y6 binary OPVs. The JSC and FF improvement of ternary OPVs should be ascribed to comprehensively optimal photon harvesting, exciton dissociation and charge transport in ternary active layers. The more efficient charge separation and transport process in ternary active layers can be confirmed by the magneto-photocurrent and impedance spectroscopy experimental results, respectively. This work provides new insight into constructing highly efficient ternary OPVs with well compatible Y6 and its derivative as acceptor. [ABSTRACT FROM AUTHOR]

Abstract Efficient semitransparent ternary polymer solar cells (PSCs) are fabricated with narrow band gap material PTB7-Th as donor, two narrow band gap nonfullerene materials BDTThIT-4F and IEICO-4F as one alloyed acceptor. Firstly, the content of IEICO-4F in acceptors is optimized in opaque PSCs with 100 nm Ag as electrode, power conversion efficiency (PCE) of the optimized opaque PSCs arrives to 12.03% with 50 wt% IEICO-4F in the alloyed acceptor. The 1 nm Au/10 nm Ag is designed to replace 100 nm Ag as semitransparent electrode. The semitransparent electrode exhibits high transmittance in visible light range and low transmittance in long wavelength range, which is beneficial to improve photon harvesting of active layers prepared with narrow band gap materials. The semitransparent ternary PSCs exhibit a PCE of 9.40% with 24.6% average visible transmittance from 370 nm to 740 nm, which should be among the highest values for semitransparent PSCs. This work indicates that ternary strategy may have great potential in preparing efficient semitransparent PSCs with two narrow band gap nonfullerene materials. Graphical abstract Semitransparent PSCs (ST-PSCs) were prepared with 1 nm Au/ 10 nm Ag as electrode. The 9.40% PCE and 24.6% AVT are achieved in semitransparent ternary PSCs. This work indicates that ternary strategy has great potential in obtaining efficient semitransparent PSCs with two ultra-narrow band gap acceptors. fx1 Highlights • Ternary strategy is beneficial to prepare efficient semitransparent PSCs. • The optimized semitransparent ternary PSCs exhibit PCE of 9.40% and AVT of 24.6%. • The PCE and AVT of PSCs are simultaneously improved by incorporating IEICO-4F. [ABSTRACT FROM AUTHOR]

Fullerene-free acceptors and ternary strategy have aroused extensive attention due to their great potential for improving efficiency and stability of organic solar cells (OSCs). Here, we demonstrate high-efficiency and air stable OSCs by combining the benefits of fullerene-free acceptors and ternary strategy. A polymer acceptor N2200 as the third component is incorporated with PBDB-T:ITIC to fabricate fullerene-free ternary OSCs, which achieve an outstanding power conversion efficiency (PCE) of 11.41% and excellent stability in air conditions. Compared with the binary cells, the performance improvement of ternary OSCs is mainly attributed to the enhanced photon harvesting and optimized morphology of active layers. Replacing ITIC by a similar acceptor ITIC-Th or IT-M in the ternary OSCs, the optimized PCE of 11.40% or 12.10% can be achieved for PBDB-T:ITIC-Th:N2200-based or PBDB-T:IT-M:N2200-based cells, respectively. [ABSTRACT FROM AUTHOR]

A carbazole-based hole-transporting material named 4,4′,4′′,4′′′-(9-octylcarbazole-1,3,6,8-tetrayl) tetrakis(N,N-bis(4-methoxyphenyl)aniline) (CZ-TA) has been developed through a one-step facile synthesis approach. The solution-processed planar perovskite solar cells (PVSCs) with 50 nm thick CZ-TA hole selective layer (HSL) contributes a power conversion efficiency of 18.32%, comparable to the most commonly used 200 nm spiro-OMeTAD (18.28%) HSLs. The improved hole extraction, transport and reduced recombination are found to endow CZ-TA-based devices with impressive fill factors over 81.0%. Importantly, the unit cost of HSL in PVSCs using CZ-TA can be as low as only 1/80 of that of spiro-OMeTAD, indicating that CZ-TA could be a promising candidate as HSLs for commercialization of the low-cost PVSC technology. [ABSTRACT FROM AUTHOR]

A smart ternary strategy was designed to simultaneously improve utilization of excitons on PCDTBT and enhance photon harvesting in long wavelength range by doping appropriate SQ into the dominating PCDTBT:PC 71 BM system. The phase separation can be finely optimized by adjusting SQ doping ratio, resulting in efficient charge carrier transport channels and the enhanced photon harvesting in the ternary active layers. The dopant SQ provides a potential route for further utilizing the excitons on PCDTBT, especially for the excitons unattainable to the PCDTBT/PC 71 BM interfaces. The excitons on PCDTBT can transfer their energy to SQ through Förster energy transfer, and then be dissociated into free charge carriers at SQ/PC 71 BM interface. The holes generated on SQ can be effectively transferred to PCDTBT and then transported along the channels formed by PCDTBT to anode. Consequently, the champion PCE of ternary solar cells arrives to 7.62% with 9 wt% SQ doping ratio in donors, which is much higher than the PCE of 6.54% for PCDTBT:PC 71 BM-based or 1.95% for SQ:PC 71 BM-based solar cells. [ABSTRACT FROM AUTHOR]

Ternary strategy exhibits some apparent advantages to improve the performance of polymer solar cells (PSCs), such as using two donors or two acceptors to enhance photon harvesting and maintain the simple cell fabrication process. The power conversion efficiency (PCE) of PSCs was increased from 4.89% to 5.54% by doping 4 wt% SMPV1 into Si-PCPDTBT:PC 71 BM binary system. The PCE improvement should be attributed to the enhanced photon harvesting in the visible light range and optimized charge carrier transport by doping appropriate SMPV1 in the active layers. The champion PCE values were also increased from 4.89% to 5.73% or from 5.54% to 6.44% for binary or the optimized ternary PSCs by CHCl 3 solvent vapor annealing treatment. The positive effect of appropriate SMPV1 doping ratio should be attributed to the efficient energy transfer from SMPV1 to Si-PCPDTBT and the more balanced charge carrier transport in the ternary active layers. The energy transfer from SMPV1 to Si-PCPDTBT can be clearly confirmed from the absorption, photoluminescence (PL) spectra and time-resolved transient PL spectra of pure and blend films. The more balanced charge carrier transport can be further demonstrated from the corresponding hole-only and electron-only devices. [ABSTRACT FROM AUTHOR]

A series of polymer solar cells (PSCs) were fabricated with narrow band gap polymer poly{[4,9-dihydro-4,4,9,9-tetra(4-hexylbenzyl)-s-indaceno[1,2-b:5,6-b0]-dithiophene-2,7-diyl]-alt-[2,3-bis(3-(octyloxy)phenyl)-2,3-dihydro-quinoxaline-2,20-diyl] (PIDTDTQx), small molecule material 2,4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl]squaraine (DIB-SQ), or their blend as electron donor, and [6,6]-phenyl-C71-butyric acid methyl ester (PC 71 BM) as electron acceptor. The champion power conversion efficiency (PCE) of ternary PSCs arrives to 6.49% with a short circuit current density ( J SC ) of 11.56 mA/cm 2 and a fill factor (FF) of 66% when the DIB-SQ doping ratio in donors is 9 wt%. The champion PCE values of binary PSCs with PIDTDTQx:PC 71 BM or DIB-SQ:PC 71 BM as the active layers are 5.47% or 1.78%, respectively. An apparent PCE improvement of 18.6% was obtained from the optimized ternary PSCs compared with binary PSCs with PIDTDTQx:PC 71 BM as the active layers. The underlying reason of PCE improvement was investigated from the absorption spectral complementary, photoluminescence emission quenching, intermolecular charge transfer, and the balance of charge carrier transport in ternary active layers. [ABSTRACT FROM AUTHOR]

Abstract: A series of solution-processed small molecular solar cells (SMSCs) were fabricated with 2,4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl] (DIB-SQ) and [6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM) as the active layer. The cells with MoO3 as anode interfacial layer and LiF as cathode interfacial layer have the maximum power conversion efficiency (PCE) 2.68%, with short circuit density (J sc ) of 8.2mA/cm2, open circuit voltage (V oc ) of 0.9V and fill factor (FF) of 36.3% under 100mW/cm2 illumination intensity. The key parameters, including J sc V oc , and FF of cells with MoO3 as anode interfacial layer and LiF as cathode interfacial layer, are improved about 54.7%, 26.9%, and 23.5% compared with these of cells using PEDOT:PSS as anode interfacial layer and LiF as cathode interfacial layer. The underlying reasons are mainly attributed to the effect of MoO3 layer on charge carrier collection and morphology of active layer. The effect of illumination intensity on the performance of cells was also discussed in detailed. [Copyright &y& Elsevier]

Abstract: The performance of polymer solar cells (PSCs), based on poly(3-hexylthiophene) (P3HT) and [6,6]phenyl-C71-butyric acid methyl ester (PC71BM), were improved by adding poly[(4,8-bis-(2-ethylhexyloxy)-benzo[1,2-b:4,5-b′](dithiophene)-2,6-diyl-alt-(4-(2-ethylhexanoyl)-thieno[3,4-b]thiophene)-2,6-diyl] (PBDTTT-C). The absorption region of the ternary blend films is extended into near infrared region (NIR). Power conversion efficiency (PCE) of the ternary blend PSCs is improved to 2.48% with 6% PBDTTT-C, which is 27% higher than the binary blend PSCs. The dominant mechanism for the PCE improvement could be attributed to the well balance between photon harvest and charge carrier transport by doping proper concentration PBDTTT-C. The energy transfer or charge carrier transfer directly between P3HT and PBDTTT-C was investigated, which are found to be positive for the performance improvement of ternary blend PSCs. [Copyright &y& Elsevier]

Abstract: Two series of P3HT-based polymer solar cell (PSCs) only with different electron acceptors PC70BM or PC60BM were investigated under the same conditions. The PSCs with PC70BM as the electron acceptor exhibit a relatively strong and broad absorption in the visible range and high external quantum efficiency, which results in a relatively high open circuit voltage (V oc ) of 0.62V, short circuit current density (J sc ) of 11.85mA/cm2 and power conversion efficiency (PCE) of 3.52%. The PSCs with PC60BM as the electron acceptor have a relatively low V oc of 0.58V, J sc of 10.68mA/cm2 and PCE of 3.02% due to the weak absorption of PC60BM in the visible light range. The function of PC70BM instead of PC60BM as electron acceptor could be summarized as follows: i) the strong absorption PC70BM in the visible range results in much more photon harvesting; ii) the relatively low electron mobility and relatively big size of PC70BM molecule influences the charge transporting and phase separation. The ultimate performances of PSCs are codetermined by the photon harvesting, exciton dissociation, charge carrier transport and collection. [Copyright &y& Elsevier]

Abstract: Recent years, the power conversion efficiency (PCE) of normal configuration organic solar cells (OSCs) has obtained rapid progress to reach more than 6% under standard illumination, which is reasonable value for the commercial criterion. More and more research attention has been paid on the stability and lifetime of OSCs. A novel structural OSCs with high work function metal or metal oxide as the top electrode and low work function metal as the bottom anode is proposed and named as inverted configuration OSCs. The inverted configuration OSCs with high work function metal as top cathode could improve OSCs''s lifetime, i.e., protecting cells from the damage by oxygen and moisture in air. Furthermore, the inverted configuration OSCs is the appealing alternative to the conventional regular structure due to the inherent vertical phase separation in the polymer active layers and high stability or long device lifetime. The inverted configuration OSCs have not only achieved an impressive PCE of 4.4%, but also exhibited an exceptional device lifetime without encapsulation. In this review article, the recent developments and vital researches on the inverted configuration OSCs are summarized. [Copyright &y& Elsevier]

The power conversion efficiency (PCE) of organic photovoltaics (OPVs) has exceeded 18% with narrow bandgap, non-fullerene materials Y6 or its derivatives when used as an electron acceptor. The PCE improvement of OPVs is due to strong photon harvesting in near-infrared light range and low energy loss. Meanwhile, ternary strategy is commonly recognized as a convenient and efficient means to improve the PCE of OPVs. In this review article, typical donor and acceptor materials in prepared efficient OPVs are summarized. From the device engineering perspective, the typical research work on ternary strategy and tandem structure is introduced for understanding the device design and materials selection for preparing efficient OPVs. [ABSTRACT FROM AUTHOR]

Semitransparent solar cells not only can generate electricity but also exhibit promising application in facades and roofs of building, as well as the coatings of vehicle. Ideal semitransparent solar cells should have a high utilization efficiency of ultraviolet and near infrared photons, and maintain an appropriate balance between absorption and transparency in visible light range. Organic semiconducting materials with adjustable optical band gap own great potential in preparing highly efficient semitransparent organic solar cells (OSCs). There are great challenges in achieving semitransparent electrodes with good conductivity and high transmittance in visible light range, as well as high reflectance in ultraviolet and near infrared range. In this critical review, we summarize the recent progress of semitransparent OSCs, concentrating on organic semiconducting materials, semitransparent top electrode and device engineering. Semitransparent OSCs have attracted more and more attention due to its great potential in energy source in door, electricity-generating windows, building-integrated photovoltaics and agricultural greenhouse. Semitransparent OSCs have attracted more and more attention due to its great potential in electricity-generating windows, building-integrated photovoltaics and agricultural greenhouse. This review comprehensively summarizes recent progresses of organic material, semitransparent top electrode and device engineering, the challenges on achieving semitransparent OSCs are highlighted to promote the development of this field. Image 1 • Recent development of organic materials with strong ultraviolet or near infrared absorption were summarized. • The key parameters for evaluating the performance of semitransparent OSCs were discussed. • This review comprehensively summarized recent progress of transparent top electrodes. • The light management methods and device designs are firstly comprehensively reported. [ABSTRACT FROM AUTHOR]

Ternary strategy has been confirmed as an efficient method to improve the power conversion efficiency (PCE) of organic photovoltaics (OPVs). The 15.7% PCE is achieved from PM6:Y6 based binary OPVs. One nonfullerene acceptor Br-ITIC and fullerene derivative PC 71 BM are selected as the third component on the basis of efficient binary OPVs, respectively. The optimized ternary OPVs exhibit 16.4% and 16.2% PCE with Br-ITIC and PC 71 BM as the third component, respectively, corresponding to the short circuit current density (J SC) of 25.5 mA cm−2 vs. 25.6 mA cm−2, open circuit voltage (V OC) of 0.854 V vs. 0.836 V and fill factor (FF) of 75.1% vs. 75.6%. The advantage on photovoltaic parameters of two ternary OPVs may be recombined into one cell by employing PC 71 BM as the fourth component. A 16.8% PCE is achieved from the optimized quaternary OPVs, resulting from the further increased J SC of 25.8 mA cm−2 and FF of 76.4% compared with the optimized ternary OPVs. The third party certificated PCE of quaternary OPVs is 16.2%. In comparison to 15.7% PCE of the binary OPVs, about 4.5% and 7.0% PCE improvement are step-by-step achieved from the optimized ternary and quaternary OPVs, respectively. Multi-components strategy may provide enough room to achieve highly efficient OPVs. Based on highly efficient binary OPVs, Br-ITIC and PC 71 BM were successively incorporated into the active layer as the third and the fourth component, leading to the step-by-step PCE improvement from 15.7% to 16.4% and then to 16.8%. Image 1 • A PCE of 16.8% is achieved in the optimized quaternary OPVs. • Photogenerated exciton distribution can be optimized by employing multi-components strategy. • PC 71 BM can act as a morphology regulator to optimize molecular arrangement and phase separation. [ABSTRACT FROM AUTHOR]

Small molecules organic photovoltaics (SMPVs) were prepared with DR3TSBDT as donor, narrow band gap material Y6 and broad band gap material PC 71 BM as acceptor. The Y6 based binary SMPVs exhibit a power conversion efficiency (PCE) of 10.53%, with short-circuit current density (J SC) of 21.67 mA cm−2, open-circuit voltage (V OC) of 0.879 V and fill factor (FF) of 55.21%. A 12.84% PCE is achieved from the optimized ternary SMPVs with 40 wt% PC 71 BM in acceptors, which is attributed to the enhanced J SC of 22.19 mA cm−2 and FF of 67.27% resulting from the well-optimized phase separation with PC 71 BM as morphology regulator. Hollow spherical structure of PC 71 BM with high electron mobility may connect Y6 molecules to form the more continuous electron transport channels in ternary active layers. Meanwhile, DR3TSBDT molecular arrangement can be markedly adjusted by incorporating PC 71 BM to form 3D texture structure. The well-optimized phase separation degree and molecular arrangement in ternary active layers can well support the enhanced FFs of ternary SMPVs compared with that of binary SMPVs. Over 21% PCE improvement is achieved by employing ternary strategy with 40 wt% PC 71 BM in acceptors, the 12.84% PCE should be among the highest values of SMPVs. A power conversion efficiency of 12.84% is achieved in small molecules organic photovoltaics by incorporating PC 71 BM as morphology regulator. Image 1 • A PCE of 12.84% is achieved in the optimized ternary SMPVs. • Over 21% PCE improvement is achieved by employing ternary strategy. • The J SC and FF are simultaneously increased with PC 71 BM as morphology regulator. [ABSTRACT FROM AUTHOR]

A series of organic solar cells (OSCs) were prepared with J71 as donor and IT-4F, T6Me or T6Me:IT-4F as acceptor(s), respectively. The two binary OSCs exhibit the same open circuit voltage (V OC), complementary short circuit current density (J SC) and fill factor (FF). The same V OC of binary OSCs with J71 as donor indicate the similar lowest unoccupied molecular orbits (LUMO) levels of IT-4F and T6Me. Meanwhile, IT-4F and T6Me have complementary photon harvesting range, exhibiting great potential in preparing efficient ternary OSCs. The optimized ternary OSCs exhibit a 13.16% power conversion efficiency (PCE) with 50 wt% IT-4F in acceptors, resulting from the enhanced J SC and FF. The FFs of ternary OSCs can be gradually improved along with IT-4F content increase, indicating that the two acceptors may prefer to form an alloyed state. The alloyed state of two acceptors should be beneficial to Förster energy transfer from IT-4F to T6Me, providing another channel for improving exciton utilization efficiency. This work indicates that alloyed model should have great potential in preparing efficient ternary OSCs with large content of the third component by fully exerting the advantages of used materials. Ternary organic solar cells with 13.16% efficiency by recombining the advantages of used materials and the corresponding binary OSCs. Image 1 • The optimized ternary OSCs exhibit a PCE of 13.16%, which should be among the highest values of J71 based OSCs. • The >13% improvement in PCE is attributed to the optimized photon harvesting and morphology of ternary active layers. • The exciton utilization efficiency is enhanced through efficient energy transfer from IT-4F to T6Me. [ABSTRACT FROM AUTHOR]

• The LbL APSCs exhibit a PCE of 18.55%, which should be among the highest values for LbL APSC with eco-friendly solvent. • The exciton dissociation in ternary LbL APSCs can be promoted by the formation of alloyed state. • The smaller energy loss of optimized LbL APSCs is conductive to the improvement of V OC. In this work, a series of eco-friendly solvent-processed all-polymer solar cells (APSCs) were fabricated by employing the sequentially spin-coating method. Two polymer donor materials PBQx-TCl and PM6 were deliberately selected due to their similar chemical structure, preferring to form the alloyed state for better exciton dissociation and hole transport in the layer-by-layer (LbL) APSCs. The better exciton dissociation between PBQx-TCl and PM6 can be confirmed from PL spectra of neat and blend films, as well as the short-circuit current densities (J SC) of special cells without acceptor layer. The optimized ternary LbL APSCs with 30 wt% PM6 in donor layer exhibit the power conversion efficiency (PCE) of 18.55 %, originating from the simultaneously improved J SC of 25.16 mA cm−2, open-circuit voltage (V OC) of 0.966 V, and fill factor of 76.33 %. The increased V OC of ternary LbL APSCs is mainly attributed to the decreased energy loss due to the good compatibility of the two polymer donors. The PCE of 18.55 % should be among the highest value for LbL APSCs processed by eco-friendly solvent. [ABSTRACT FROM AUTHOR]

The PCE of 15.83% is achieved for the optimized opaque PSCs with PM6:Y6 as active layer of 100 nm, resulting from the well-balanced photon harvesting and charge collection. The PCE and AVT of semitransparent PSCs can be simultaneously optimized by adjusting the thickness of Ag layer. The PCE of 12.37% and AVT of 18.6% are achieved for semitransparent PSCs with 10 nm thick Ag and 1 nm thick Au layers as electrode. A series of opaque and semitransparent polymer solar cells (PSCs) were fabricated with PM6:Y6 as active layers, and 100 nm Al or 1 nm Au/(20, 15, 10 nm) Ag layer as electrode, respectively. The power conversion efficiency (PCE) of opaque PSCs arrives to 15.83% based on the optimized active layer with a thickness of 100 nm, resulting from the well-balanced photon harvesting and charge collection. Meanwhile, the 100 nm PM6:Y6 blend film exhibits a 50.5% average visible transmittance (AVT), which has great potential in preparing efficient semitransparent PSCs. The semitransparent electrodes were fabricated with 1 nm Au and different thick Ag layers, exhibiting a relatively high transmittance in visible light range and relatively low transmittance in near infrared range. The PCE and AVT of the semitransparent PSCs can be adjusted from 14.20% to 12.37% and from 8.9% to 18.6% along with Ag layer thickness decreasing from 20 to 10 nm, respectively, which are impressive values among the reported semitransparent PSCs. [ABSTRACT FROM AUTHOR]

A PCE of 19.13% is achieved in ternary SS-PSCs with two well-compatible polymer donors (PM1 and D18) and an efficient non-fullerene acceptor (L8-BO), resulting from all-around enhanced J SC , V OC and FF. The optimized vertical phase separation, enhanced charge transport and collection should be the critical factors for PCE improvement of ternary SS-PSCs. [Display omitted] • The optimized ternary SS-PSCs achieved higher PCE of 19.13% than binary SS-PSCs. • Two polymers PM1 and D18 with similar chemical structures were selected as donors. • Energy transfer from D18 to PM1 provides an additional exciton utilization channel. Series of sequentially spin-coated polymer solar cells (SS-PSCs) are fabricated with donor layers containing PM1, D18 or PM1:D18 and sequentially spin-coated L8-BO acceptor layer. Photon harvesting of donor layers could be enhanced by optimizing the weight ratios of PM1 to D18 due to their distinct optical band-gap. The optimized ternary SS-PSCs exhibit a power conversion efficiency of 19.13%, resulting from the simultaneously enhanced short-circuit-current density (J SC) of 27.20 mA/cm2, open-circuit voltage (V OC) of 0.90 V and fill factor of 78.53% in comparison to those of PM1/L8-BO based SS-PSCs. The increased J SC s of ternary SS-PSCs is due to the enhanced photon harvesting and efficient exciton utilization assisted by an additional channel from D18 to PM1 through energy transfer. The increased V OC of optimal ternary SS-PSCs benefits from the little larger V OC of binary SS-PSCs with D18 as donor layer. The donor/acceptor interfacial energy is slightly increased by incorporating D18 in donor layer, which is conducive to form the optimized vertical phase separation to decrease charge recombination loss. This work indicates that ternary strategy is also a versatile and effective method in improving the performance of SS-PSCs. [ABSTRACT FROM AUTHOR]

The length and conformation of solubilizing side chains in π-conjugated polymers impact polymers' self-assembling properties in thin-film devices. To reveal the effect of different bisalkylthio side chains, four copolymers containing bisalkylthio side chain modifying two-dimensional benzo[1,2- b :4,5 -b ′]dithiophene (BDT) donor with (5,6-difluoro-4,7-di(thiophen-2-yl)benzo[ c ][1,2,5]thiadiazole (BDff) acceptor have been developed and studied in this report. The different absorption maxima ( λ max ) of PBDTT-DS1-BTff , PBDTT-DS2-BTff , PBDTT-DS3-BTff and PBDTT-DS4-BTff are 578, 574, 591 and 594 nm in CHCl 3 solution, respectively, indicating different aggregation behaviors. The devices based on PBDTT-DS1-BTff didn't reveal high PCEs due to its poor miscibility with PC 71 BM compared to those with other polymers. The devices blending PBDTT-DS2-BTff with PC 71 BM exhibited a highest PCE of 5.82%, with an enhanced J SC of 11.06 mA cm −2 , a V OC of 0.92 V and a FF of 57.2%. This work demonstrates that suitable side chain lengths in π-conjugated polymers are of great significance in optimizing the performance of polymers based solar cells. [ABSTRACT FROM AUTHOR]

The conventional LbL APSCs exhibit an optimal PCE of 15.28% with polymer PM6 as donor and polymer PYF- T -o as acceptor, which is higher than 14.97%, 13.03% and 8.54% obtained from the conventional BHJ APSCs, inverted BHJ APSCs and inverted LbL APSCs, benefiting from the higher exciton ultilization efficiency in conventional LbL active layers. [Display omitted] • Conventional LbL APSCs exhibit higher PCE of 15.28% than conventional BHJ APSCs. • Efficient energy transfer provides an additional exciton utilization channel in conventional LbL APSCs. • LbL structure has great potential in achieving highly efficient APSCs. Series of conventional and inverted all-polymer solar cells (APSCs) were prepared with polymer PM6 as donor and polymer PYF- T -o as acceptor based on layer-by-layer (LbL) or bulk heterojunction (BHJ) structure. The power conversion efficiency (PCE) of 15.28% and 14.97% can be achieved in conventional LbL and BHJ APSCs, respectively. The relatively high PCE of conventional LbL APSCs is mainly originated from short circuit current density (J SC) improvement caused by optimized phase separation and more ordered molecular arrangement for efficient charge extraction and transport in layered active layers. Meanwhile, the efficient energy transfer from PM6 to PYF- T -o should provide an additional exciton utilization channel, which is also responsible for relatively high performance in conventional LbL APSCs. It is worth noting that the inverted APSCs exhibit low PCE as compared to that of corresponding conventional APSCs, especially for the inverted LbL APSCs with only 8.54% PCE. The markedly inferior PCE in inverted LbL APSCs is mainly attributed to the insufficient PYF- T -o exciton dissociation, which can be demonstrated from the greatly low EQE spectra in long wavelength region as compared to that of other type APSCs. This work provides more deep insight on the dynamic process in LbL active layers, which should contribute to the construction of highly efficient APSCs based on LbL processing method. [ABSTRACT FROM AUTHOR]