High-efficiency inverted polymer solar cells with double interlayer

We have studied the performance of normal and inverted bulk-heterojunction solar cells with an active layer composed of a blend of poly[(4,4'-bis(2-ethylhexyl)dithieno[3,2-b:2',3'-d]silole)-2,6-diyl-alt-(2,1,3-benzothiadiazole)-4,7-diyl] (PDTS-BTD) and {6,6}-phenyl-C71 butyric acid methyl ester (PC(71)BM). For inverted cells, a thin layer of ZnO nanoparticles and MoO(3) were used as interlayers for the bottom cathode and the top anode respectively. To enhance the device performance, a thin film of 4,4',4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine (MTDATA) was used along with MoO(3) as an anode interlayer to improve the hole extraction from the photoactive layer to the anode. The inverted polymer solar cells with double interlayer exhibit a higher power conversion efficiency of 6.45% compared to the conventional cell of 4.91% due to efficient charge extraction and favorable vertical morphology of active layer blend. Our ultraviolet photoemission spectroscopy results indicate that the formation of band bending due to interlayer leads to the enhancement in hole extraction.     

Synthesis and characterization of cyclopentadithiophene-based low bandgap copolymers for all-polymer solar cells

Three conjugated copolymers based on cyclopentadithiophene (CPDT) units, namely, poly{4,4-bis(2-ethylhexyl)cyclopenta[2,1-b:3,4-b′]dithiophene-2,6-diyl-alt-2,1,3-benzothiadiazole-4,7-diyl} (P1), Poly{4,4-bis(2-ethylhexyl)cyclopeanta[2,1-b:3,4-b′]dithiophene-2,6-diyl-alt-2,1,3-benzoselenadiazole-4,7-diyl} (P2) and Poly{4,4-bis(2-ethylhexyl)cyclopenta[2,1-b:3,4-b′]dithiophene-2,6-diyl-alt-N,N′-bis(2-ethylhexyl)-3,4,9,10-perylene diimide-1,7-diyl} (P3) have been synthesized via Stille coupling reaction. The polymers were characterized by ¹H NMR spectroscopy, gel permeation chromatography (GPC), UV–vis absorption spectroscopy, and cyclic voltammetry. These new polymers exhibit broad and strong absorption between 500 and 800 nm. The highest occupied molecular orbital energy levels of polymers vary between ?4.98 and ?5.27 eV and the lowest unoccupied molecular orbital energy levels range from ?3.43 to ?3.70 eV. By employing P1 and P2 as electron donors (D) and P3 as electron acceptor (A), all-polymer solar cells with bulk heterojunction structure have been fabricated. Preliminary results indicate that these devices show higher open circuit voltage (V _OC ) in comparison with the traditional polymer/fullerene systems of P1 and P2 blended with the acceptor (6,6)-phenyl C₆₁-butyric acid methyl ester (PCBM).     

Preparation and photovoltaic properties of the composite based on CdS nanorod arrays and PCPDTBSe

Vertically aligned CdS nanorod arrays (NRA) were synthesized through facile one-step and template-free hydrothermal approach directly on indium tin oxide (ITO)-coated glass substrates. A low band gap polymer, namely Poly[4,4-bis(2-ethylhexyl)cyclopenta[2,1-b:3,4-b’]dithiophene-2,6-diyl-alt-2,1,3-benzoselenadiazole-4,7-diyl] (PCPDTBSe) was synthesized by the Stille coupling reaction. An organic/inorganic hybrid solar cell prototype device was fabricated based on the as-prepared CdS NRA and PCPDTBSe (ITO/CdS arrays/PCPDTBSe/Au), showing a power conversion efficiency of 0.10 %.     

Substituent effect on color tuning of red light emission in photoluminescence and electroluminescence of red fluorophore

Typical small red light-emitting molecules for organic light emitting diodes (OLEDs) were highly susceptible to fluorescence concentration quenching in solid state. Red fluorophores, (2Z, 2'Z)-3, 3'-[4,4"-bis(dimethylamino)-1,1':4',1"-terphenyl-29',5'-diyl]bis(2-phenylacrylonitrile) (ABCV-P), (2E, 2'E)-3,3'-[4,4"-bis(dimethylamino)-1,1':4',1"-terphenyl-2',5'-diyl]bis[2-(2-thienyl)acrylonitrile] (ABCV-Th) and (2Z, 2'Z)-3,3'-[4,4"-bis(dimethylamino)-1,1':4',1"-terphenyl-2',5'-diyl]bis[2-(2-naphthyl)acrylonitrile] (ABCV-Np), capable of preventing fluorescence concentration quenching were designed and synthesized. These compounds have intramolecular charge transfer (ICT) properties which were estimated by measurement of UV-Visible absorption and photoluminescence (PL) emission spectra with variation of solvent polarity (n-Hexane/Chloroform = 99/1, 1/1; Chloroform; Methylene chloride). The magnitude of ICT for ABCV-Th was measured to be the largest and that for ABCV-Np was slightly larger compared to that for ABCV-P. The magnitude of ICT resulted in a shift of peak wavelength of PL emission. Therefore, this result well supported substituent effect on the color change of PL emission. The peak wavelengths of photoluminescence for ABCV-P, ABCV-Np and ABCV-Th were observed to be 607.5, 611.5 and 617.5 nm, respectively, and those of EL spectra were measured to be 612.5, 619.5, 621.0 nm, respectively. The emission maxima of PL and EL spectra for these red fluorescent compounds were well correlated with substituent effect on ICT for them.     

Synthesis and photovoltaic properties of new near infrared absorption polymers based on C and N-bridged dithiophene and diketopyrrolopyrrole units

Two novel diketopyrrolopyrrole-based conjugated copolymers, namely, poly{[4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b′]dithiophene-2,6-diyl]-alt-[3,6-bis(bithiophen-5-yl)-2,5-di-(2-ethylhexyl)-pyrrolo[3,4-c]pyrrole-1,4-dione]} (P1) and poly{[N-(2-ethylhexyl)-dithieno[3,2-b:2′,3′-d]pyrrole-2,6-diyl]-alt-[3,6-bis(bithiophen-5-yl)-2,5-di-(2-ethylhexyl)-pyrrolo[3,4-c]pyrrole-1,4-dione]} (P2), have been designed and synthesized by Stille coupling reaction. The resulting copolymers exhibited very broad and strong absorptions in the visible and near-infrared region. Through cyclic voltammetry measurements, it was found that P1 possesses a lower highest occupied molecular orbital energy level (?5.14 eV) compared to that of P2 (?4.98 eV). The bulk heterojunction photovoltaic devices were fabricated by using the two copolymers as the donor and [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) as the acceptor in the active layer. The maximum power conversion efficiency of 1.48 % was obtained based on the blend of P1:PCBM = 1:3(w/w) with open circuit voltage (V _OC ) of 0.66 V and short circuit current (J _SC ) of 6.36 mA/cm², under the illumination of AM 1.5, 100 mW/cm².     

Panchromatic photon-harvesting by hole-conducting materials in inorganic-organic heterojunction sensitized-solar cell through the formation of nanostructured electron channels

Additional photon-harvesting by hole transporting materials in Sb(2)S(3)-sensitized solar cell is demonstrated through the formation of electron channels in the hole transporter such as P3HT (poly(3-hexylthiophene)) and PCPDTBT(poly(2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']dithiophene)-alt-4,7(2,1,3-benzothiadiazole)) that can act as both a hole conductor and light absorber. As a result, the short-circuit current density is improved with an increment in overall efficiency. These findings provide new insights into use of light-absorbing conjugated polymers as a hole conductor in the inorganic-organic heterojunction sensitized solar cells.     

Preparation and photovoltaic properties of the composite based on porous In2S3 films and PCPDTBT

Large-scale porous indium sulfide (In₂S₃) films were synthesized via a facile one-step non-template hydrothermal process. A low band gap polymer, namely Poly[4,4 -bis(2-ethylhexyl)cyclopenta[2,1-b:3,4-b′]dithiophene-2,6-diyl-alt-2,1,3-benzothiadia zole-4,7-diyl](PCPDTBT) was synthesized by the Stille coupling reaction. A preliminary photovoltaic performance measurement of the fabricated device based on the as-prepared In₂S₃ porous film and PCPDTBT(ITO/In₂S₃ porous film/PCPDTBT/Au) shows a power conversion efficiency of 0.12 % under an illumination of 100 mW/cm^?2.     

Synthesis and characterization of platinum(II) complexes with 2,2'-bipyridine derivative supporting ligands

The reaction of the [Pt(bpy-R)Cl2](bpy-R: R=H (2,2'-bipyridine); R=CH3 (4,4'-dimethyl-2,2'-biypridine (DM-bpy), 3,3'-5,5'-tertamethyl-2,2'-bipyridiyl (TM-bpy)) with 1,4-Bis(5'-2',2"-bipyridine)benzene (bpy-Ph-bpy) affords the following mono- and di-platinum complexes of [(bpy)Pt(bpy-Ph-bpy)][PF6]2 (1), [(bpy)Pt(bpy-Ph-bpy)Pt(bpy)])[PF6]4 (2), [(DM-bpy)Pt(bpy-Ph-bpy)])][PF6]2 (3), and [(TM-bpy)Pt(bpy-ph-bpy)[PF6]2 (4), respectively. These complexes were characterized by NMR, IR, UV/VIS, PL and cyclic voltammetry. The internal quantum yields of these platinum(II) complexes are very high (0.83-0.99) and these complexes emit light at deep blue regions (373-417 nm). The redox behavior of complexes 1 and 2 shows quasi-reversible process.     

The effect of the molecular structure on the optoelectronic properties of a fluorophore for use in organic light-emitting diodes

A novel yellow light-emitting material, (2Z)-3-[4,4"-bis(dimethylamino)-1,1':4',1"-terphenyl-2'-yl]-2-phenylacrylonitrile (BDAT-P), having the modified molecular structure from red fluorescent compound, (2Z, 2'Z)-3,3'-[4,4"-bis(dimethylamino)-1,1':4',1"-terphenyl-2',5'-diyl]bis(2-phenylacry-lonitrile) (ABCV-P), was synthesized in order to study the effect of the molecular structure on the optoelectronic properties of a light-emitting material. UV-visible absorption and photoluminescence (PL) emission peaks measured in various solvent systems were summarized in Table I. In the respective solvent system, the bathochromic shift of PL emission peak relative to the peak of UV-visible absorption was much larger for ABCV-P with two electron donor-acceptor pairs than for BDAT-P with one electron donor-acceptor pair. EL emission peaks of devices using BDAT-P and ABCV-P as the host emitters measured to be 573 and 613 nm, respectively. Commission Internationale de l'Eclairage (CIExy) coordinate of device using BDAT-P was measured to be (0.4855, 0.5021) at 7 V, which was correspond to the yellow color.     

Polymer/polymer blend solar cells with 2.0% efficiency developed by thermal purification of nanoscale-phase-separated morphology

We have fabricated polymer/polymer blend solar cells consisting of poly(3-hexylthiophene) as the electron donor and poly{2,7-(9,9-didodecylfluorene)-alt-5,5-[4',7'-bis(2-thienyl)-2',1',3'-benzothiadiazole]} as the acceptor. The power conversion efficiency (PCE) was strongly dependent on solvents employed for spin coating. The best PCE of 2.0% was obtained for thermally annealed devices prepared from a chloroform solution, in contrast to devices fabricated from chlorobenzene and o-dichlorobenzene solutions. On the basis of the morphology-performance relationship in the polymer blends examined by atomic force microscopy and the photoluminescence quenching measurements, we conclude that the highly efficient performance is achieved by thermal purification of nanoscale-phase-separated domains formed by spin coating from chloroform.     

Organic light-emitting diodes having carbon nanotube anodes

Single-walled carbon nanotube (SWNT) films on flexible PET (polyethyleneterephthalate) substrates are used as transparent, flexible anodes for organic light-emitting diodes (OLEDs). For polymer-based OLEDs having the structure: SWNT/PEDOT-PSS:MeOH/TFB (poly(9,9-dioctylfluorene-co-N-(4-butylphenyl)diphenylamine)) + TPD-Si(2) (4,4'-bis[(p-trichlorosilylpropylphenyl)phenylamino]biphenyl) /BT (poly(9,9-dioctylfluorene-co-benzothiadiazole))/CsF/Al, a maximum light output of 3500 cd/m(2) and a current efficiency of 1.6 cd/A have been achieved. The device operational lifetime is comparable to that of devices with Sn-doped In(2)O(3) (ITO)/PET anodes. The advantages of this novel type of anode over conventional ITO are discussed.     

A highly efficient polymer non-fullerene organic solar cell enhanced by introducing a small molecule as a crystallizing-agent

Non-fullerene organic solar cells (OSCs) have attracted tremendous interest because of their potential to replace traditional expensive fullerene-based OSCs. To further increase the power conversion efficiency (PCE), it is necessary to offset the narrow absorption of the non-fullerene materials, which is often achieved by adding an additive (>10?wt%) to form a ternary blend. However, a high ratio of the third component can often be detrimental to the active layer morphology and can increase the complexity in understanding the device physics toward rationally designed improvements. In this work, we introduce 2,4-bis-[(N,N-diisobutylamino)-2,6-dihydroxyphenyl]-4-(4-diphenyliminio) squaraine (ASSQ) in the poly [(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl) benzo [1,2-b:4,5-b′] dithiophene)-co-(1,3-di(5-thiophene-2-yl)-5,7-bis(2-ethylhexyl) benzo [1,2-c:4,5-c′] dithiophene-4,8-dione)] (PBDB-T): 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno [2,3-d:2′,3′-d′]-s-indaceno [1,2-b:5,6-b′] dithiophene (ITIC) as an active layer “crystallizing-agent”. Through detailed morphology characterization, we find that the addition of 4?wt% ASSQ assists ITIC organization order and promotes PDBD-T:ITIC aggregation in the preferential face-on orientation. In addition, we demonstrate that the ASSQ and PBDB-T show efficient exciton dissociation in the ternary blend over Förster resonance energy transfer (FRET). We reveal using surface potential and solubility measurements that a ASSQ-ITIC co-crystalline structure forms which facilitates a significant improvement in the device PCE, from 8.98% to 10.86%.     

Molecular design of copolymers based on polyfluorene derivatives for Bulk-heterojunction-type solar cells

Poly{[2,7-(9,9′-dihexylfluorene)]-alt-[4,7-di(thiophen-2-yl)benzo[c][1, 2, 5]thiadiazole]} (PFDTBT) with low band gap was reported as an intriguing and promising donor in Bulk-heterojunction-type solar cells. In this paper, based on the structure of PFDTBT, three new kinds of donor materials: poly{[2,7-(9,9′-dihexylfluorene)]-alt-[4,7-di(thiophen-2-yl)-[1, 2, 5]thiadiazolo[3,4-d]pyridazine]} (PFDTTDP), poly{[2,7-(9,9′-dihexyloxyfluorene)]-alt-[4,7-di(thiophen-2-yl)-[1, 2, 5]thiadiazolo[3,4-d]pyridazine]} (POFDTTDP), and poly{[2,6-(4,4-dihexyl)-4H-cyclopenta[2,1-b;3,4-b’]-dithiophene)-alt-[4-(1,3,4-thiadiazol-2-yl)-7-(thiophen-2-yl)-[1, 2, 5]thiadiazolo[3,4-d]pyridazine]} (PCPTTTDP), were designed and computed by density function theory (DFT). The electronic, optical and photovoltaic properties, and charge transport rates were investigated. The reorganization energies for holes and electrons are around 0.11 and 0.08 eV, respectively. It indicates that PFDTTDP, POFDTTDP, and PCPTTTDP are good candidates for donor material. Especially, when 6,6-phenyl-C61-butyric acid methyl ester (PC₆₁BM) functions as acceptor, PCPTTTDP has the most appropriate highest occupied molecular orbital and lowest unoccupied molecular orbital energy, and has the broadest absorption in the near-infrared region.     

Efficient and 1,8-diiodooctane-free ternary organic solar cells fabricated via nanoscale morphology tuning using small-molecule dye additive

The ternary strategy for incorporating multiple photon-sensitive components into a single junction has emerged as an effective method for optimizing the nanoscale morphology and improving the device performance of organic solar cells (OSCs).In this study,efficient and stable ternary OSCs were achieved by introducing the small-molecule dye (5E,5'E)-5,5'-(4',4″-(1,2-diphenylethene-1,2-diyl)bis(biphenyl-4',4-diyl))bis(methan-1-yl-1-ylidene)bis(3-ethyl-2-thioxothia zolidin-4-one) (BTPERn) into poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiopheneco-3-fluorothieno[3,4-b]thiophene-2-carboxylate] (PTB7-Th):[6,6]-phenyl C71 butyric acid methyl ester (PC71BM) blend films processed using a 1,8-diiodooctane (DIO)-free solvent.The incorporation of BTPE-Rn enhanced the short-circuit current density and fill factor of the ternary OSCs compared with those of binary OSCs.An investigation of the optical,electronic,and morphological properties of the ternary blends indicated that the third component of BTPE-Rn not only promoted the photon utilization of blends through the energy-transfer process but also improved the electron mobility of the blends owing to the fullerene-rich nanophase optimization.More importantly,this ternary strategy of utilizing a small-molecule dye to replace the photounstable DIO additive enhanced the operational stability of the OSCs.     

A 3-Fluoropyridine Manipulating the Aggregation and Fibril Network of Donor Polymers for Eco-Friendly Solution-Processed Versatile Organic Solar Cells

The development of eco-friendly solvent-processed organic solar cells (OSCs) suitable for industrial-scale production should be now considered the imperative research. Herein, asymmetric 3-fluoropyridine (FPy) unit is used to control the aggregation and fibril network of polymer blends. Notably, terpolymer PM6(FPy = 0.2) incorporating 20% FPy in a well-known donor polymer poly[(2,6-(4,8-bis(5-(2-ethylhexyl-3-fluoro)thiophen-2-yl)-benzo[1,2-b:4,5-b’]dithiophene))-alt-(5,5-(1’,3’-di-2-thienyl-5’,7’-bis(2-ethylhexyl)benzo[1’,2’-c:4’,5’-c’]dithiophene-4,8-dione)] (PM6) can reduce the regioregularity of the polymer backbone and endow them with much-enhanced solubility in eco-friendly solvents. Accordingly, the excellent adaptability for fabricating versatile devices based on PM6(FPy = 0.2) by toluene processing is demonstrated. The resulting OSCs exhibit a high power conversion efficiency (PCE) of 16.1% (17.0% by processed with chloroform) and low batch-to-batch variation. Moreover, by controlling the donor-to-acceptor weight ratio at 0.5:1.0 and 0.25:1.0, semi-transparent OSCs (ST-OSCs) yield significant light utilization efficiencies of 3.61% and 3.67%, respectively. For large-area (1.0 cm²) indoor OSC (I-OSC), a high PCE of 20.6% is achieved with an appropriate energy loss of 0.61 eV under a warm white light-emitting diode (3,000 K) with the illumination of 958 lux. Finally, the long-term stability of the devices is evaluated by investigating their structure–performance–stability relationship. This work provides an effective approach to realizing eco-friendly, efficient, and stable OSCs/ST-OSCs/I-OSCs.     

A study on white organic light-emitting diodes co-doped with red fluorescent and blue phosphorescent dopants

White organic light-emitting diodes (WOLEDs) have drawn increasing attention due to their potential use in various applications such as solid-state lighting and backlight of liquid crystal displays and full-color OLEDs of red, green, and blue pixel. N,N'-dicabazolyl-3,5-benzene (mCP), the host material, was co-doped with Iridium (III) bis[(4,6-difluorophenyl)-pyridinato-N,C2']-picolinate (FIrpic), which functions not only as phosphorescent sensitizer but also blue emitter, and (2Z,2'Z)-3,3'-[4,4"-bis (dimethylamino)-1,1':4',1"-terphenyl-2',5'-diyl]bis (2-phenylacrylonitrile) (ABCV-P), which is a red fluorescent material. The fabricated device structures were as follows: (device A) Indium tin oxide (ITO)/N,N'-bis-(1-naphyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (NPB)/(mCP)/mCP:ABCV-P (1%)/4,7-diphenyl-1,10-phenanthroline (Bphen)/lithium quinolate (Liq)/aluminum (Al), (device B) ITO/NPB/mCP/mCP:FIrpic (8%)/Bphen/Liq/Al and (device C) ITO/NPB/mCP/mCP:FIrpic:ABCV-P (8%, 1%)/Bphen/Liq/Al, respectively. Phosphorescent FIrpic harvesting both singlet and triplet excitions not only emitted blue light but also transferred energy to fluorescent ABCV-P. The maximum luminance efficiency, external quantum efficiency, and luminance of white light device were measured to be 5.95 cd/A, 2.45% and 2500 cd/m2, respectively. The white device gave practically white light with the Commision Internationale de l'Eclairage (CIE(xy)) coordinate of (0.44, 0.49) which was close to warm white color (CIE(xy) = 0.45, 0.45).     

25th Anniversary Article: High‐Mobility Hole and Electron Transport Conjugated Polymers: How Structure Defines Function

The structural organization of three different families of semicrystalline π‐conjugated polymers is reported (poly(3‐hexylthiophene) (P3HT), poly[2,6‐(4,4‐bis‐alkyl‐4H‐cyclopenta‐[2,1‐b;3,4‐b0]‐dithiophene)‐alt‐4,7‐(2,1,3‐benzothiadiazole)](cyclopentadithiophene‐benzothiadiazole) (CDT‐BTZ) and poly(N,N"‐bis‐2‐octyldodecylnaphtalene‐1,4,5,8‐bis‐dicarboximide‐2,6‐diyl‐alt‐5,5–2,2‐bithiophene (P(NDI2OD‐T2))). These have triggered significant interest for their remarkable charge‐transport properties. By performing molecular mechanics/dynamics simulations with carefully re‐parameterized force fields, it is illustrated in particular how the supramolecular organization of these conjugated polymers is driven by an interplay between the length and nature of the conjugated monomer unit and the packing of their alkyl side chains, and to what extent it impacts the charge‐carrier mobility, as monitored by quantum‐chemical calculations of the intermolecular hopping transfer integrals. This Progress Report is concluded by providing generic guidelines for the design of materials with enhanced degrees of supramolecular organization.     

Performance evaluation of dye-sensitized solar cells (DSSCs) based on metal-free thieno[3,2-b]indole dyes

Journal of Materials Science: Materials in Electronics - A series of thieno[3,2-b]indole-based dyes (IS 1–10) was readily synthesized in three steps from 2-(thien-2-yl)thieno[3,2-b]indole as...     

In Situ GIWAXS Analysis of Solvent and Additive Effects on PTB7 Thin Film Microstructure Evolution during Spin Coating

The influence of solvent and processing additives on the pathways and rates of crystalline morphology formation for spin‐coated semiconducting PTB7 (poly[[4,8‐bis[(2‐ethylhexyl)oxy]benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl][3‐fluoro‐2‐[(2‐ethylhexyl)‐carbonyl]‐thieno[3,4‐b]thiophenediyl]]) thin films is investigated by in situ grazing incidence wide‐angle X‐ray scattering (GIWAXS) and optical reflectance, to better understand polymer solar cell (PSC) optimization approaches. In situ characterization of PTB7 film formation from chloroform (CF), chlorobenzene (CB), and 1,2‐dichlorobenzene (DCB) solutions, as well as CB solutions with 1% and 3% v/v of the processing additives 1‐chloronapthalene (CN), diphenylether (DPE), and 1,8‐diiodooctane (DIO), reveals multiple crystallization pathways with: (i) single‐solvent systems exhibiting rapid (<3 s) crystallization after a solvent boiling point‐dependent film thinning transition, (ii) solvent + additive systems exhibiting different crystallization pathways and crystallite formation times from minutes (CN, DPE) to 1.5 h (DIO). Identifying crystalline intermediates has implications for bulk‐heterojunction PSC morphology optimization via optimized spin‐casting processes.     

Dithiapyrannylidenes as efficient hole collection interfacial layers in organic solar cells

One inherent limitation to the efficiency of photovoltaic solar cells based on polymer/fullerene bulk heterojunctions (BHJs) is the accumulation of positive charges at the anodic interface. The unsymmetrical charge collection of holes and electrons dramatically decreases the short-circuit current. Interfacial layers (IFLs) such as poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) have no effect on the unbalanced electron/hole transport across the BHJ. We report here on the use of dithiapyrannylidenes (DITPY), a new class of planar quinoid compounds, as efficient hole-transporting/electron-blocking layers in organic solar cells based on poly(3-hexylthiophene)/[6,6]-phenyl-C(61)-butyric acid methyl ester (P3HT:PCBM) BHJs. Inserting a 15-nm-thick IFL of 4,4'-bis(diphenyl-2,6-thiapyrannylidene) (DITPY-Ph(4)) between the indium-tin oxide electrode and the P3HT:PCBM BHJ prevents detrimental space-charge effects and favors recombination-limited currents. Current-sensing atomic force microscopy reveals a drastic increase of the hole-carrying pathways in DITPY-Ph(4) compared to PEDOT:PSS. In ambient conditions, photovoltaic cells using DITPY-Ph(4) exhibit an 8% increase in the current density, although the conversion efficiency remains slightly lower compared to PEDOT:PSS-based devices. Finally, we present a detailed analysis of the photocurrent generation, showing that DITPY-Ph(4) IFLs induce a transition from unproductive space-charge-limited currents to recombination-limited currents.