Bulk Heterojunction Layer Research Articles

Impact of the bilayer electron transport layer in the donor acceptor bulk heterojunctions for improved inverted organic photovoltaic performance

Functionalization at interface of the electron transport layer and the organic polymeric donor and non-fullerene acceptor bulk heterojunction layer in photovoltaic devices that have an inverted structure, is a unique strategy for improving performance. Here we demonstrate improved interfacial nanomorphology of the well-known PTB7-Th donor and IEICO-4F acceptor bulk heterojunction (BHJ) on an atomic layer deposited (ALD) ultrathin titanium oxide (TiO2) passivated sol–gel grown zinc oxide (ZnO) electron transport bilayer and highlight how this is correlated to the overall organic photovoltaic device performance. Synchrotron-based grazing incidence wide-angle X-ray scattering (GIWAXS) has been used to demonstrate an enhanced face-on conformation within the BHJ with highly crystalline ZnO/TiO2/BHJ layers and this is greatest for the very thinnest of TiO2 layers on ZnO (ZnT1), from just two deposition cycles, relative to both four (ZnT2) and eight (ZnT3) cycles. Photovoltaic devices with BHJs grown over ZnT1, showed an overall average increase of 30.3 ± 0.5 % in the power conversion efficiency (PCE 10.3 ± 0.5 %), a 14.3 ± 1 % increase in the fill-factor, FF (60.1 ± 1 %), 2.9 ± 0.05 % improvement in Voc (0.70 ± 0.05 mV) and 13.6 ± 0.5 % higher JSc (24.2 ± 0.5 mA/cm2), compared to the control device,with a best efficiency of 11.1 ± 0.5 % PCE, 61.9 ± 1 % FF, 0.70 ± 0.5 mV Voc and 25.0 ± 0.5 mA/cm2Jsc. We conclude that the molecular crystal conformation of the organic donor acceptor BHJ layer can be partly controlled through the ETL along with an enhanced organic inorganic interface which strongly influences the OPV performance.

Highly Efficient Nonfullerene Organic Solar Cells with Nickel Oxide Hole‐Transporting Layer: Using Dipole‐Induced Energy‐Level Modification

To date, poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is the most commonly used hole‐transporting material (HTM) for nonfullerene acceptor (NFA) organic solar cell (OSCs) due to its high hole conductivity and reproducibility. However, considering the significant breakthroughs made by novel donor and NFA combinations such as PM6 and Y6, the development of HTMs which can outperform PEDOT:PSS is very limited. Here, for the first time, high‐performance NFA OSCs based on simple and solution‐processed nickel oxide HTMs with high power conversion efficiency (PCE) and stability are reported. Two different kinds of hydroquinone sulfonic acid (HSA) salts, which have a permanent dipole moment, are added to NiO solution. Due to the interfacial dipole moment generated by these salts and effective work function modulation of NiO, efficient hole transportation at the interface between hole‐transporting layer and bulk heterojunction (BHJ) layer by minimizing the energetic barrier is promoted. As a result, using PM6 and the Y6‐BO‐4F‐based BHJ layer, the PCE of 14.19% with very high open‐circuit voltage of 0.86 V is achieved, which is comparable with that of PEDOT:PSS‐based OSCs. For 1200 h under ambient atmosphere, OSCs based on NiO containing HSA salts demonstrate enhanced ambient stability compared to that of PEDOT:PSS.

Influence of Acid-Doped Poly(ethylene imine) Interlayers on the Performance of Polymer:Nonfullerene Solar Cells.

This work reports that ultrathin polymeric films doped with organic acid molecules can act as an electron-transporting interfacial layer in polymer:nonfullerene solar cells. The polymeric interfacial layers, which consist of poly(ethylene imine) (PEI) doped with 3-hydroxypropane-1-sulfonic acid (HPSA) at various HPSA molar ratios, are introduced between transparent indium-tin oxide (ITO) electrodes and polymer:nonfullerene bulk heterojunction layers. The HPSA-doped PEI (PEI:HPSA) films are optically translucent in the wavelength range of ≈300-800nm, while the acidity of PEI solutions reached ≈pH = 7 at HPSA = 30 mol%. The power conversion efficiency of solar cells is improved by doping 20 mol% HPSA due to the increased short circuit current density without open circuit voltage reduction. The improvement in solar cell performances is attributed to an adequate control of HPSA doping ratios, which spares undoped amine units of PEI for making sufficient net dipole layers with ITO surfaces and makes permanent charges for high electrical conductivity in the layers. The surface morphology and doped states are characterized with atomic force microscopy and X-ray photoelectron spectroscopy.

Revealing conflicting effects of solvent additives on morphology and performance of non-fullerene organic photovoltaics under different illuminance conditions

The use of solvent additives is effective for controlling the morphology and efficiency of non-fullerene bulk-heterojunction (BHJ) organic photovoltaics (OPVs) under both indoor and outdoor conditions. In this study, we examined the effects of solvent additives on the morphology and photovoltaic operation of non-fullerene OPVs under different illuminance conditions. Solvent additives (e.g., 1,8-diiodooctane) improved molecular packing and charge transport in non-fullerene BHJ layers, increasing the power conversion efficiency (PCE) under 1-sun illumination. However, incorporating the solvent additives promoted the formation of a crystallization-induced roughened surface and an isolated-non-fullerene domain in the intermixing region. These unexpected morphological features increased the degree of trap-assisted charge recombination and leakage current, significantly reducing the PCE of non-fullerene OPVs at low light levels corresponding to indoor lighting. Understanding the effect of solvent additives inspires us to further control the morphological features of the non-fullerene OPVs by fine-tuning the solvent-additive concentration beyond the globally accepted level. This was effective for optimizing the indoor PCE of non-fullerene OPVs (21.71%), which exceeded that of the conventionally accepted reference (18.02%). This study provides guidelines for understanding the critical roles of solvent additives and optimizing the morphology of non-fullerene BHJs for high-performance indoor OPV applications.

Low-voltage-modulated perovskite/organic dual-band photodetectors for visible and near-infrared imaging

Visible and near-infrared (NIR) light dual-band photodetectors (PDs) have potential applications in signal detection, bioimaging, optical communications and safety monitoring. Herein, we report an ultrafast perovskite/organic heterojunction dual-mode PD with a voltage-modulated photoresponse range in visible and NIR spectra. The PD, comprising a perovskite layer to absorb visible light (500–810 nm) and an organic bulk heterojunction layer for NIR light absorption (810–950 nm), exhibited a switchable spectral response in the visible or NIR bands. The voltage-modulated visible and NIR photoresponses of the PD were attributable to controlled charge photogeneration in perovskite and organic blend thin films under different bias polarities. The device exhibited peak responsivities of 93.5 and 102.2 mA/W in the visible and NIR bands, respectively; a high detectivity of 4.3 × 109 Jones (at forward bias of 0.7 V and incident 625 nm light) and 1.6 × 1012 Jones (at reverse bias of –1.5 V and incident 900 nm light); a fast microsecond response time; and a wide dynamic range (>120 dB) both in the visible mode and NIR mode. Also, this voltage-modulated dual-band PD shows promising applications in visible light and NIR imaging, which is proven by demonstrating a PD array with 25 pixels (5 × 5).

Integrated Ideal‐Bandgap Perovskite/Bulk‐Heterojunction Solar Cells with Efficiencies > 24%

Here, the authors report a highly efficient integrated ideal-bandgap perovskite/bulk-heterojunction solar cell (IPBSC) with an inverted architecture, featuring a near infrared (NIR) polymer DTBTI-based bulk-heterojunction (BHJ) layer atop guanidinium bromide (GABr)-modified FA0.7 MA0.3 Pb0.7 Sn0.3 I3 perovskite film as the photoactive layer. The IPBSC shows cascade-like energy level alignment between the charge-extractionlayer/perovskite/BHJ and efficient passivation effect of BHJ on perovskite. Thanks to the well-matched energy level alignment and high-quality ideal bandgap-based perovskite film, an efficient charge transfer occurs between the charge-extraction-layer/perovskite/BHJ. Moreover, the NIR polymer DTBTI on the perovskite film leads to an improved NIR light response for the IPBSC. In addition, the O, S and N atoms in the DTBTI polymer yield a strong interaction with perovskite, which is conducive to reducing the defects of the perovskite and suppressing charge recombination. As a result, the solar cell achieves a power conversion efficiency (PCE) of 24.27% (certificated value at 23.4% with 0.283-volt voltage loss), currently the recorded efficiency for both IPBSCs and Pb-Sn alloyed PSCs, and which is over the highest efficiency of perovskite-organic tandem solar cell. Moreover, the thermal, humidity and long-term operational stabilities of the IPBSCs are also significantly improved compared with the control PSCs.

Enhancement of resistive switching behavior of organic resistive random access memory devices through UV-Ozone treatment

We fabricated organic resistive random-access memory (RRAM) devices using a low-cost solution-process method. All the processes were performed at temperatures below 135 °C under ambient atmospheric conditions. The RRAM resistive switching layer was formed from a polymer-fullerene bulk heterojunction using poly(3-hexylthiophene-2,5-diyl) (P3HT) and (6,6)-phenyl C61 butyric acid methyl ester (PCBM). The fabricated organic RRAM device exhibited typical nonvolatile bipolar resistive switching behavior with an ON/OFF ratio of ∼40, but it provided a low endurance of 27 cycles. Therefore, for enhanced stability, simple UV–Ozone (UVO) treatment was applied to the P3HT:PCBM organic bulk heterojunction layer. The organic RRAM device with UVO treatment exhibited an enhanced performance with an ON/OFF ratio of ∼400 and an endurance of 47 cycles. In addition, complementary resistive switching behavior was observed. The conduction mechanisms of the organic RRAM device were investigated by fitting the measured I–V data to numerical equations, and Schottky emission and Ohmic conduction were the main conduction mechanisms for the high-resistance and low-resistance states for the RRAM device with or without UVO treatment.

Boosting Efficiency of Non‐Fullerene Organic Solar Cells Via Introducing Multidimensional Second Acceptors

The active layer bulk heterojunction (BHJ) blends with a suitable phase separation and crystallization are of great importance to the exciton dissociation, charge transfer, and ultimately the efficiency of the organic solar cells (OSCs). Herein, an effective approach is developed to modulate the molecule's crystallization and phase separation of BHJ blends via introducing a multidimensional (MD) second acceptor. The efficiency of the OSCs can be largely boosted when the cross‐shaped MD acceptors are introduced into the BHJs as a third component. The ternary OSCs based on PTB7‐Th:IEICO‐4F:SFCPDT exhibit a higher power conversion efficiency (PCE) (PCE = 13.29%) than that of the PTB7‐Th:IEICO‐4F binary system (PCE = 11.67%). It is found that the ternary films deliver higher and more balanced carrier mobility, as well as reduced carrier recombination. The positive effect can be also extended to the PBDB‐T‐2F: IT‐4F‐based ternary system. When FLIDT and SFIDT are employed as the third component, the PCE values can be increased from pristine 11.98–12.42% and 13.16%, respectively. It is anticipated to further boost the efficiency of the non‐fullerene OSCs by rationally designing the structure of the third component for a state‐of‐the‐art active layer system.

Dual additive strategy to regulate the phase separation of bulk heterojunction layer for efficiency enhancement in non-fullerene organic solar cells

The phase separation of bulk heterojunction (BHJ) layer is critical for the exciton dissociation, charge transport and recombination in non-fullerene organic solar cells (OSCs), therefore accurately regulating the BHJ phase separation must be one of the significant strategies to enhance the performance of non-fullerene OSCs. In this paper, dual additive strategy (1,8-diiodooctane (DIO) and methanol (MeOH)) is proposed to regulate the phase separation of PBDB-TF:IT-4F layer. Experimental studies reveal that this dual additive strategy could decrease domain size which is beneficial to exciton dissociation. Moreover, the extraction of low boiling point MeOH from the BHJ film can bring some IT-4F dissolved in DIO:MeOH:CB toward to the BHJ surface and thus improve the vertical distribution and form an efficient bi-continuous charge transport routes in BHJ layer for balancing charge transport in OSCs. Consequently, with dual additive DIO and MeOH, the short circuit current density raises from 19.79 to 21.13 mA cm −2 , fill factor enhances from 67.73% to 70.86%, and the power conversion efficiency increases from 11.26% to 12.72% with ∼13% improvement. Notably, this dual additive strategy is free of complicated treatment which is suitable for practical application. • Dual additive strategy was proposed to regulate the phase separation of PBDB-TF:IT-4F layer. • Smaller domain size and bi-continuous charge transfer channels were formed with dual additive. • This dual additive strategy relieve complex treatment which is suitable for practical use.

Strain-durable dark current in near-infrared organic photodetectors for skin-conformal photoplethysmographic sensors

SummarySensitive detection of near-infrared (NIR) light is applicable to variety of optical, chemical, and biomedical sensors. Of these diverse applications, NIR photodetectors have been used as a key component for photoplethysmography (PPG) sensors. In particular, because NIR organic photodetectors (OPDs) enable fabrication of stretchable and skin-conformal PPG sensors, they are attaining tremendously increasing interest in both academia and industry. Herein, we report strain-durable and highly sensitive NIR OPDs using an organic bulk heterojunction (BHJ) layer. For effective suppression of dark current, we employed BHJ combination consisting of PTB7-Th:Y6 which forms high energy barrier against transport-injected holes. The optimized OPDs exhibited high specific detectivity up to 2.2 × 1012 Jones at 800 nm. By constructing the devices on the parylene substrates, we successfully demonstrated stretchable NIR OPDs and high-performance skin-conformal PPG sensors.

Sequential stacking of a thin BHJ layer acting as a morphology regulator for efficiency enhancement in non-fullerene ternary solar cells

Although ternary-blend solar cells (TSCs) featuring alloyed systems with two acceptors can display high power conversion efficiencies (PCEs) while minimizing energy loss, it can be difficult to control the morphology of the alloyed ternary blend. In this study we developed a gradient ternary (Gradient-Ternary) device architecture by transferring a bulk-heterojunction (BHJ) layer over the spin-coated ternary blend to enhance the PCEs of alloyed TSCs. The Gradient-Ternary architecture, which was similar to that of a compositional-gradient BHJ blend, featured a vertically stratified morphology that established efficient charge extraction pathways, thereby mitigating the recombination loss faced by the corresponding Ternary blend, while concurrently improving the photocurrent, relative to that of the Ternary blend, without suffering losses in any of the other photovoltaic parameters. A champion efficiency of 16.5% was obtained using the Gradient-Ternary architecture (PM6:Y6:ITIC/PM6:ITIC) was higher than those of the Ternary (PM6:Y6:ITIC) and Binary (PM6:Y6) architectures exhibiting an efficiency of 15.7% and 15.0% respectively. Applying such gradient architectures might also accelerate the efficiency of other organic solar cells.

Hole Transfer Prompted by Viscous Oligomer Solid Additives in Non-Fullerene Bulk-Heterojunction Layers

Hole Transfer Prompted by Viscous Oligomer Solid Additives in Non-Fullerene Bulk-Heterojunction Layers

High-Performance organic photodiodes for Blue-Light hazard detection

In this study we incorporated a PffBT4T-2OD:PC71BM bulk-heterojunction (BHJ) active layer in the layer structure ITO/ZnO/BHJ/MoO3/Ag, obtaining high-performance organic photodiodes (OPDs) for application in blue-light hazard (BLH) detection. The high crystallinity of PffBT4T-2OD resulted in the OPD displaying high performance even when the thickness of the BHJ layer was up to 850 nm. The efficient OPD suppressed charge injection (from the metal contacts), thereby providing state-of-the-art performance: external quantum efficiencies of greater than 70% (380–710 nm), a value of Jd of 1.18 × 10-9 A cm−2 (-2 V), and high detectivity [2.9 × 1013 Jones, −2 V (710 nm)]. The observed ultra-high cut-off frequency [greater than800 kHz (at 530 nm), with rise/fall times of less than 350 ns at reverse biases of less than −3 V] exceeded that of a silicon photodiode and made the system suitable for use in image photosensors and medical monitoring. The wide linear dynamic range (LDR, 530 nm) of the OPD (139 dB at −1 V, from 2.2 × 10-4 to 2.5 × 10-11 A cm−2) encompassed the mesopic and scotopic vision regimes. Combined with the design of a BLH filter, we calculated the environmental BLH weighted irradiation power density [WDBLH = CB × JSC (current density of diode)] to evaluate the BLH effect for various light sources and commercially available lenses; here CB (12.69, reported herein) is a corrective constant for BLH photodetectors. Finally, our design allowed ready determination of the ratio of blue-violet and blue-green light.

Lateral organic-inorganic hybrid Vis-NIR photodetectors based on GaN nanowires promoting photogenerated carriers transfer

The narrow bandgap of the low-energy near-infrared (NIR) polymer would lead to overlap between adjacent energy levels, which is a major barrier to the preparation of Vis-NIR polymer bulk heterojunction (BHJ) photodetectors with small responsivity and photocurrent. In this study, a high-performance lateral inorganic-organic hybrid photodetector was constructed to eliminate this barrier by combining GaN nanowires (GaN-NWs) with PDPP3T:PC61BM-based BHJ. In stage one, high-quality GaN-NWs were synthesized by the catalyst-free CVD method. The mechanism for controlling GaN-NWs morphology by adjusting the NH3 flow rate was revealed. In stage two, the GaN-NWs with large electron mobility were used to accelerate the transfer of photogenerated carriers in the BHJ layer. Finally, compared with the BHJ device, the BHJ/GaN device demonstrated obvious improvements in responsivity and photocurrent at the wavelength between 400 and 1000 nm. The responsivity and photocurrent increased over 20-fold at the NIR band of 800–900 nm. Besides, owing to the energy level gradient effect, the BHJ/GaN device has a response speed of 7.8/<5.0 ms, which increases over three orders of magnitude than that of the GaN-NWs-based device (tr/tf: 7.1/10.9 s). Therefore, the novel device structure proposed in this work holds great potential for preparing high-performance Vis-NIR photodetectors.

Investigation of Degradation Mechanism of Y6-Based Inverted Organic Solar Cells and Their Utilization in Durable Near-Infrared Photodetection.

The device durability of inverted organic solar cells (OSCs) is investigated based on Y6, which is an effective nonfullerene acceptor for high-performance OSCs. The durability of Y6-based inverted OSCs is poor and it can be caused by aggregation of Y6 in the bulk-heterojunction layer due to heating by continuous photo-irradiation (≈65 °C, 100 mW cm-2 , and 72 h). It is found that the aggregation of Y6 is suppressed at a low temperature (≈50 °C), and that the Y6-based devices can be useful as a photodurable near-infrared detector upon continuous laser irradiation.

Nanoscale heterogeneous distribution of surface energy at interlayers in organic bulk-heterojunction solar cells

<h2>Summary</h2> Surface energy of the underneath interlayer plays a crucial role in determining the morphology of bulk-heterojunction (BHJ) film in solution-processed organic solar cells (OSCs). However, little attention has been paid to this perspective at the microscopic level. In this study, we demonstrate an effective strategy to tune the nanoscale heterogeneous distribution of surface energy (HeD-SE) at interlayers through incorporating two-dimensional (2D) MoS₂ nanosheets, which modulate the component distribution, molecular orientation, and phase separation in the upper BHJ layers, leading to suppressed charge recombination and increased charge extraction in devices with enhanced power conversion efficiency (PCE) and device stability. Furthermore, we explore the relationship among the different surface energies of BHJs between the donor and the acceptor, the nanoscale HeD-SE at interlayers, and the PCEs of the resultant devices. This work reveals the impact of nanoscale heterogeneity in the distribution of surface energy in the underneath interlayers on the BHJ morphology and device performance in OSCs.

Impact of the reverse bias voltage on the lifetime of polymer solar cells

We report an investigation into the impact of applying a large reverse bias voltage during current–voltage (J-V) sweeps on the degradation rate of solar cells based on poly[N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) and [6-6]-phenyl C71-butyric acid methyl ester (PC70BM), under air mass 1.5 simulated solar irradiation. The degradation rate was found to be significantly slower when devices were characterized using frequent J-V sweeps with a large reverse bias component (-7 V to 1 V), with a decrease in power conversion efficiency of 24% after ∼ 100 hrs of light exposure. In contrast, devices scanned from −1 V to 1 V degrade by 72% in the same time period. The decay in the photovoltaic performance was found to be related to an increase in the series resistance and a decrease in the shunt resistance of the devices over time. Further characterization of the bulk heterojunction layer under irradiation conditions indicates that this behavior might be caused by the decreasing mobility of the charge carriers due to the formation of the defects or traps in the layer, induced by the photo-oxidation process. The frequent application of a large reverse bias sweep most likely helps de-trap the charge carriers and slows down the device degradation. Impedance analysis indicated that during the decay of PCDTBT:PC70BM devices the bulk layer became more resistive with time, and applying large and frequent reverse bias sweeps during testing could significantly slow down this process. The charge carrier extraction time was found to increase from 7 μs to more than 400 μs after photo-degradation. These findings demonstrate that repeated application of a reverse bias voltage can affect device degradation, and therefore that the specific details of J-V characterization should be reported alongside device lifetime claims.

Highly Selective Cu Staining of Sulfur-Containing Polymers Facilitates 3D Nanomorphology Reconstruction of Polymer:Fullerene Blends in Organic Solar Cells by FIB-SEM Tomography.

The distinction of different organic materials in phase mixtures is hampered in electron microscopy because electron scattering does not strongly differ in carbon-based materials that mainly consist of light elements. A successful strategy for contrast enhancement is selective staining where one phase of a material mixture is labeled by heavier elements, but suitable staining agents are not available for all organic materials. This is also the case for bulk-heterojunction (BHJ) absorber layers of organic solar cells, which consist of interpenetrating networks of donor and acceptor domains. The domain structure strongly influences the power conversion efficiency, and nanomorphology optimization often requires real-space information on the sizes and interconnectivity of domains with nanometer resolution. In this work, we have developed an efficient approach to selectively stain sulfur-containing polymers by homogeneous Cu infiltration, which generates strong material contrast in scanning (transmission) electron microscopy (S(T)EM) images of polymer:fullerene BHJ layers. Cross-section lamellae of BHJ layers are prepared for STEM by focused-ion-beam milling and are attached to a Cu lift-out grid as a copper source. After thermal treatment at 200 °C for 3 h in air, sulfur-containing polymers are homogeneously infiltrated by Cu, while the fullerenes are not affected. Selective Cu staining is applied to map the phase distribution in PTB7:PC71BM BHJ layers fabricated with different processing additives to tailor the nanomorphology. The strong contrast between polymer and fullerene domains is the prerequisite for the three-dimensional reconstruction of the domain structure by focused-ion-beam/scanning-electron-microscopy tomography.

Low-Bandgap Organic Bulk-Heterojunction Enabled Efficient and Flexible Perovskite Solar Cells.

Lead halide perovskite and organic solar cells (PSCs and OSCs) are considered as the prime candidates currently for clean energy applications due to their solution and low-temperature processibility. Nevertheless, the substantial photon loss in near-infrared (NIR) region and relatively large photovoltage deficit need to be improved to enable their uses in high-performance solar cells. To mitigate these disadvantages, low-bandgap organic bulk-heterojunction (BHJ) layer into inverted PSCs to construct facile hybrid solar cells (HSCs) is integrated. By optimizing the BHJ components, an excellent power conversion efficiency (PCE) of 23.80%, with a decent open-circuit voltage (Voc ) of 1.146V and extended photoresponse over 950nm for rigid HSCs is achieved. The resultant devices also exhibit superior long-term (over 1000 h) ambient- and photostability compared to those from single-component PSCs and OSCs. More importantly, a champion PCE of 21.73% and excellent mechanical durability can also be achieved in flexible HSCs, which is the highest efficiency reported for flexible solar cells to date. Taking advantage of these impressive device performances, flexible HSCs into a power source for wearable sensors to demonstrate real-time temperature monitoring are successfully integrated.

How to Choose an Interfacial Modifier for Organic Photovoltaics Using Simple Surface Energy Considerations.

Organic photovoltaics are typically composed of at least four different materials, including the donor and acceptor components of the bulk heterojunction, the interfacial layers at each electrode, the electrodes themselves, and solution additives that may persist in the final sandwich structure. The interplay of surface energies between these different layers is profoundly complex, as the deposition and annealing of one layer on top of another may be influenced by the surface energy of these interfaces. While the energy levels of one layer with respect to adjacent layers are important to facilitate charge separation and collection at the electrodes, the relative surface energies of the interfaces in contact with the multicomponent bulk heterojunction can be beneficial or disadvantageous, or be neutral, with respect to the performance of the OPV device. Because the bulk heterojunction is a mixture of donor and acceptor polymers and/or small molecules, the accumulation of one of the components on the underlying electrode interface can be driven by surface energy considerations. A donor- or acceptor-rich interface may affect charge carrier flow to the electrode, thus affecting the overall efficiency. Here, ITO/PEDOT:PSS electrodes in forward organic photovoltaic devices are treated with five different thin interfacial layers to change the relative surface energy of this electrode with respect to the adjacent bulk heterojunction. Contact angle measurements with four probe liquids enable calculation of the surface energies, and the results are compared with the performance of forward-biased organic photovoltaic devices. Time-of-flight secondary ion mass spectrometry results substantiate the predictions of gradients in the bulk heterojunction layers, and grazing-incidence wide-angle X-ray scattering measurements show the impact on the polymer crystallites. Thus, a simple algorithm based on surface energy considerations may inform which interfacial layer for a given bulk heterojunction in an organic photovoltaic device can be the most appropriate.