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The damp-heat stability and photostability of solar cells were investigated depending on the ZnO fabrication methodology. Although the initial PCEs of the devices were similar, the ZnOs affected the solar cell performance after the aging process.

Ternary-blend active layers composed of one donor and two acceptors have been actively studied to enhance the power conversion efficiency (PCE) of organic solar cells (OSCs), and numerous advances ...

Herein, we introduce for the first time that Cs2CO3 can work with SnO2 based on a facile low-temperature solution-processed as dual electron transport layers (ETL) for enhancing device performance of inverted organic solar cells (iOSCs). Aside from better morphologies, a lower work function of ETLs, and an efficient charge extraction, along with a much lower transport resistance at the interfaces are found for iOSCs using SnO2/Cs2CO3 rather than devices based on the SnO2 only. The iOSC devices with P3HT:PC60BM as an active layer, using SnO2/Cs2CO3 (0.5 mg/ml) as dual ETLs, achieved a champion power conversion efficiency (PCE) of 3.75%, which is >36% higher than that of only the based SnO2 (2.75%). Moreover, their PCEs remained at ∼94% of the initial values after storage for 4 weeks in ambient air without any encapsulations, thus demonstrating the excellent long-term device stability. Notably, for the PTB7-Th:PC70BM systems, we also achieved an impressive champion PCE of 7.78% with using SnO2/Cs2CO3 (0.5 mg/ml) as dual ETLs, meanwhile devices based on SnO2 only exhibited a humble PCE of 4.08%. We believe that SnO2/Cs2CO3 dual ETLs concept can also be applied to other optoelectronic devices such as perovskite solar cells or light-emitting diodes, where an ETL is required to ensure high efficiency.

One of the key components in inverted organic solar cells is a zinc oxide (ZnO) layer as an electron-extraction layer. However, this layer contains electron traps that decrease the electron-extraction efficiency and reduce the photovoltaic performance. In this work, we report the photovoltaic property improvement of inverted PTB7-Th:PC71BM solar cells by coating high-molecular-weight poly(N-isopropylacrylamide-co-methacrylic acid) (H-PNIPAM) on top of the ZnO layer. The H-PNIPAM film thicknesses were carefully controlled by spin-coating different concentrations of H-PNIPAM solutions to generate an optimal thickness (3–5 nm). Atomic force microscopy and X-ray photoelectron spectroscopy revealed a uniformly coated H-PNIPAM layer. The photoluminescence spectra showed that the layer reduced the number of ZnO trap states. Contact angle measurements indicated that the layer modified the ZnO surface to become more hydrophobic, resulting in good contact with photoactive films. At the same time, the treatment decr...

Fullerene-free organic solar cells (FF-OSCs) composed of a wide-bandgap polymer donor (PD) and a small-bandgap organic small-molecule acceptor (SMA) are currently showing promising power conversion efficiency with good long-term stability. Herein, we synthesized three kinds of electron deficient alkylthiazole-based PDs for FF-OSCs. The synthesized 2,5-bis(5-bromo-4-octylthiazol-2-yl)thiophene (OTz) monomer has a simple conjugated backbone structure composed of thiophene and thiazole rings and is easily synthesized from relatively cheap starting materials, thiophene and 2-decanone, with an overall yield of 48%. To evaluate the photovoltaic properties of the OTz moiety, it is copolymerized with several benzodithiophene-based comonomers. All of the PDs are semicrystalline because of the highly planar backbone structure of OTz. Among them, the PTBOTz polymer exhibits superior absorption, hole mobility and charge separation properties, and thus the photovoltaic device based on PTBOTz and the SMA exhibited the best PCE of 8.32% with excellent thermal stability. Analyzing the nanomorphology and charge separation and transport properties of the PDs and SMA, we found that sizable crystallinity without severe molecular aggregation in blend films is critical to improving the PCE as well as the thermal stability of FF-OSCs.

The julolidine based interfacial modifier (IM-J) for cathode buffer layer following the "donor-acceptor" design concept with julolidine substituent as an electron donating moiety was incoporated to improve the surface properties of ZnO. Simple treatment of metal oxide type cathode buffer materials with organic interfacial modifier induces the enhanced photovoltaic performance and could effectively overcome several interfacial problems in inverted organic photovoltaic cells (I-OPVs). We studied on the coverage of IM-J on ZnO surface with variation of solution concentrations to reduce charge recombination and macroscopic phase separation. At the optimum condition, ZnO/IM-J (0.05 w/v%), IM-J significantly decreased the surface tension (46.1 mN/m) and improved surface morphology (RMS roughness: 0.61 nm). As a result, compared to the unmodified ZnO based device, the ZnO/IM-J based I-OPVs showed significantly improved power conversion efficiency (PCE) from 7.41 to 8.07% due to the increased photocurrent density (Jsc) and fill factor (FF). It is concluded that IM-J is one of the promising candidates for controlling electronic property of ZnO buffer layer in inverted organic photovoltaic cells. Also, our interfacial modified system can be utilized in other optoelectronic devices.

Porphyrin derivatives have recently emerged as hole transport layers (HTLs) because of their electron-rich characteristics. Although several successes with porphyrin-based HTLs have been recently reported, achieving excellent solar cell performance, the chances to improve this further by molecular engineering are still open. In this work, Zn porphyrin (PZn)-based HTLs were developed by conjugating fluorinated triphenylamine (FTPA) wings at the perimeter of the PZn core for low-temperature perovskite solar cells (L-PSCs). The fluorinated PZn-HTLs (PZn–2FTPA and PZn–3FTPA) exhibited superior HTL properties compared to the nonfluorinated one (PZn–TPA). Moreover, their deeper highest occupied molecular orbital energy levels were beneficial for boosting open-circuit voltages, and their enhanced face-on stacking improved the hole transport properties. The L-PSC using PZn–2FTPA achieved the highest performance of 18.85%. Thus far, this result is one of the highest reported power conversion efficiencies among the...

Perylene diimide (PDI) based high bandgap acceptors, DTBTP, DTF2BTP, and DTF2TZP, are synthesized for use in fullerene-free organic solar cells. The two PDI rings are connected to the end of the n-type core, forming a PDI-n-type core-PDI structure. Several n-type core materials, 4,7-dithieno-2,1,3-benzothiadiazole (DTBT), 5,6-difluoro-4,7-dithieno-2,1,3-benzothiadiazole (DTF2BT), and 4,6-difluoro-2H-benzo[d][1,2,3]triazole (DTF2TZ), are incorporated in the PDI acceptors and the n-type core effect on photovoltaic properties is studies. The introduction of alkyl side chains onto the core structure weakened the intermolecular interaction, whereas fluorination of the core structure improved the backbone planarity and intermolecular ordering. DTF2BTP having a planar core structure without bulky alkyl chains yielded the best power conversion efficiency, 4.41%, when mixed with PTB7-Th donor. The n-type core structure was beneficial in terms of increasing the electron accepting properties and the absorption in the high bandgap region of non-fullerene acceptors.

We synthesized a novel wide bandgap polymer, PDTFBT, forming a weak donor (WD)-weak acceptor (WA) structure for use in organic photodetectors (OPDs) and organic solar cells (OSCs). The fluorination in the D unit and the alkoxy substitution in the A unit induced WD and WA properties, respectively. The WD-WA structure of PDTFBT effectively broadened the bandgap compared to typical D-A structures, and the S-F and S-O dipole-dipole interactions induces a highly planar backbone structure with excellent π-π stacking in the vertical direction. In OPDs, conformationally less disordered PDTFBT polymer retained the constant responsivity and significantly improved the detectivity of PDTFBT:PC71BM devices even with a thick active layer of 470 nm, contrary to the variation in the responsivity of P3HT:PC61BM devices depending on the thickness. In OSCs, the deep HOMO energy level (−5.57 eV) of PDTFBT led to high Voc of 0.92 V in PDTFBT:PC71BM devices, which was 0.3 eV higher than that of P3HT:PC61BM devices (0.62 V), resulting in 1.8-fold enhanced power conversion efficiency. We demonstrated that the WD-WA structure with S-F and S-O interactions is highly promising strategy to make wide bandgap polymers for organic photodetectors and for the bottom cell of tandem architecture.

We report the synthesis of composite interlayers using alcohol-soluble polyfluorene (ASP)-wrapped single-walled carbon nanotubes (SWNTs) and their application as electron-transport layers for efficient organic solar cells. The ASP enables the individual dispersion of SWNTs in solution. The ASP-wrapped SWNT solutions are stable for 54 days without any aggregation or precipitation, indicating their very high dispersion stability. Using the ASP-wrapped SWNTs as a cathode interlayer on zinc oxide nanoparticles (ZnO NPs), a power conversion efficiency of 9.45% is obtained in PTB7-th:PC

1-D ZnO represents a fascinating class of nanostructures that are significant to optoelectronics. In this work, we investigated the use of an eco-friendly, metal free in situ doping through a pure thiophene-sulfur (S) on low temperature processed (

We synthesized the conjugated polymers PT2OBT, PVT2OBT, and PFBT2OBT for use in organic photodetecting devices. An octyloxy benzothiadiazole (OBT) moiety was used as a weak electron-accepting building block in the polymer system to cause the dominant absorption in the green-light region via weakening the intramolecular charge transfer (ICT) interactions between adjacent electron-donating moieties. In particular, indirect X-ray detection using a scintillator requires a low leakage current; thus, we focused on designing a molecular structure that can enhance the detectivity. The difluorobenzene-incorporated PFBT2OBT polymer showed a strong edge-on orientation both in the pristine film and in the blend film; however, PT2OBT and PVT2OBT have no preferred molecular orientation in the blend film. In the edge-on structure, the alkyl side chains of PFBT2OBT align on the surface of the electrode, forming an insulating layer, which decreases the tunneling leakage current, whereas in the latter cases, the interface between the semiconducting polymer backbone and PC70BM can come into contact with the electrode, forming a pathway for the leakage current. Consequently, the PFBT2OBT:PC70BM devices showed promising detectivities of over 1013 Jones over a wide range of reverse biases of up to −2 V, resulting from their low dark current density of less than 2.3 × 10−9 A cm−2.

We report for the first time that alkali carbonates (Li2CO3, K2CO3, and Rb2CO3) based on a low-temperature solution process can be used as interfacial modifiers for SnO2 as robust electron-transport layers (ETL) for inverted organic solar cells (iOSCs). The room-temperature photoluminescence, the electron-only devices, and the impedance studies altogether suggested the interfacial properties of the alkali carbonates–modified SnO2 ETLs, which were much better than those based on the SnO2 only, provided efficient charge transport, and reduced the charge recombination rates for iOSCs. The iOSCs using the polymer donor poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b′]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl] and the fullerene acceptor phenyl-C70-butyric acid methyl ester as the active layer showed the average power-conversion efficiencies (PCEs) based on ten devices of 6.70, 6.85, and 7.35% with Li2CO3-, K2CO3-, and Rb2CO3-modified SnO2 as ETLs, respectively; these are more than 22, 24, and 33% higher than those based on the SnO2 only (5.49%). Moreover, these iOSC devices exhibited long-term stabilities, with over 90% PCEs remaining after the devices were stored in ambient air for 6 weeks without encapsulations. We believe that alkali carbonates–modified SnO2 approaches are an effective way to achieve stable and highly efficient iOSCs and might also be suitable for other optoelectronic devices where an ETL is needed, such as perovskite solar cells or organic light-emitting diodes.

The development of n-type porphyrin acceptors is challenging in organic solar cells. In this work, we synthesized a novel n-type porphyrin acceptor, PZn-TNI, via the introduction of the electron withdrawing naphthalene imide (NI) moiety at the meso position of zinc porphyrin (PZn). PZn-TNI has excellent thermal stability and unique bimodal absorption with a strong Soret band (300–600 nm) and weak Q-band (600–800 nm). The weak long-wavelength absorption of PZn-TNI was completely covered by combining the low bandgap polymer donor, PTB7-Th, which realized the well-balanced panchromatic photon-to-current conversion in the range of 300–800 nm. Notably, the one-step reaction of the NI moiety from a commercially available source leads to the cheap and simple n-type porphyrin synthesis. The substitution of four NIs in PZn ring induced sufficient n-type characteristics with proper HOMO and LUMO energy levels for efficient charge transport with PTB7-Th. Fullerene-free organic solar cells based-on PTB7-Th:PZn-TNI were investigated and showed a promising PCE of 5.07% without any additive treatment. To the best of our knowledge, this is the highest PCE in the porphyrin-based acceptors without utilization of the perylene diimide accepting unit.

The julolidine based interfacial modifier (IM-J) for cathode buffer layer following the "donor-acceptor" design concept with julolidine substituent as an electron donating moiety was incoporated to improve the surface properties of ZnO. Simple treatment of metal oxide type cathode buffer materials with organic interfacial modifier induces the enhanced photovoltaic performance and could effectively overcome several interfacial problems in inverted organic photovoltaic cells (I-OPVs). We studied on the coverage of IM-J on ZnO surface with variation of solution concentrations to reduce charge recombination and macroscopic phase separation. At the optimum condition, ZnO/IM-J (0.05 w/v%), IM-J significantly decreased the surface tension (46.1 mN/m) and improved surface morphology (RMS roughness: 0.61 nm). As a result, compared to the unmodified ZnO based device, the ZnO/IM-J based I-OPVs showed significantly improved power conversion efficiency (PCE) from 7.41 to 8.07% due to the increased photocurrent density (Jsc) and fill factor (FF). It is concluded that IM-J is one of the promising candidates for controlling electronic property of ZnO buffer layer in inverted organic photovoltaic cells. Also, our interfacial modified system can be utilized in other optoelectronic devices.

The susceptibility of porphyrin derivatives to light-harvesting and charge-transport operations have enabled these materials to be employed in solar cell applications. The potential of porphyrin derivatives as hole-transporting materials (HTMs) for perovskite solar cells (PSCs) has recently been demonstrated, but knowledge of the relationships between the porphyrin structure and device performance remains insufficient. In this work, a series of novel zinc porphyrin (PZn) derivatives has been developed and employed as HTMs for low-temperature processed PSCs. Key to the design strategy is the incorporation of an electron-deficient pyridine moiety to down-shift the HOMO levels of porphyrin HTMs. The porphyrin HTMs incorporating diphenyl-2-pyridylamine (DPPA) have HOMO levels that are in good agreement with the perovskite active layers, thus facilitating hole transfers from the perovskite to the HTMs. The DPPA-containing zinc porphyrin-based PSCs gave the best performance, with efficiency levels comparable to those of PSCs using spiro-OMeTAD, a current state-of-the-art HTM. In particular, PZn-DPPA-based PSCs show superior air stability, in both doped and undoped forms, to spiro-OMeTAD based devices.

Hybrid solar cells (HSCs) incorporating both organic and inorganic materials typically have significant interfacial issues which can significantly limit the device efficiency by allowing charge recombination, macroscopic phase separation, and nonideal contact. All these issues can be mitigated by applying carefully designed interfacial modifiers (IMs). In an attempt to further understand the function of these IMs, we investigated two IMs in two different HSCs structures: an inverted bilayer HSC of ZnO:poly(3-hexylthiophene) (P3HT) and an inverted bulk heterojunction (BHJ) solar cell of ZnO/P3HT:[6,6]-phenyl C61-butyric acid methyl ester (PCBM). In the former device configuration, ZnO serves as the n-type semiconductor, while in the latter device configuration, it functions as an electron transport layer (ETL)/hole blocking layer (HBL). In the ZnO:P3HT bilayer device, after the interfacial modification, a power conversion efficiency (PCE) of 0.42% with improved Voc and FF and a significantly increased Jsc was obtained. In the ZnO/P3HT:PCBM based BHJ device, including IMs also improved the PCE to 4.69% with an increase in Voc and FF. Our work clearly demonstrates that IMs help to reduce both the charge recombination and leakage current by minimizing the number of defect sites and traps and to increase the compatibility of hydrophilic ZnO with the organic layers. Furthermore, the major role of IMs depends on the function of ZnO in different device configurations, either as n-type semiconductor in bilayer devices or as ETL/HBL in BHJ devices. We conclude by offering insights for designing ideal IMs in future efforts, in order to achieve high-efficiency in both ZnO:polymer bilayer structure and ZnO/polymer:PCBM BHJ devices.

A new donor-acceptor-conjugated organic small molecule, BDT(TBT)(2), comprised of benzo[1,2-b:4,5-b']dithiophene and 2,1,3-benzothiadiazole units was designed and synthesized. The small molecule BDT(TBT)(2) in its thin film showed an absorption band in the range of 300-700 nm with an absorption edge at 650 nm and an optical band gap of 1.90 eV. As estimated from the cyclic voltammetry measurements, the HOMO and LUMO energy levels of BDT(TBT)(2) were -5.44 and -3.37 eV, respectively. The spin-coated thin film of BDT(TBT)(2) exhibited p-channel output characteristics with a hole mobility of 2.7 × 10(-6). BDT(TBT)(2), when explored as an electron-donor material in solution-processed bulk-heterojunction organic solar cells in conjunction with a PC(71)BM acceptor with an active layer thickness of 50-55 nm, generated a power conversion efficiency (PCE) of 1.18%. A more impressive PCE of ~2.9% with a short-circuit current density (J(sc)) of 7.94 mA cm(-2) and an open-circuit voltage (V(oc)) of 0.89 V was achieved when the active layer of the cell was annealed at higher temperature (~180 °C).

Three solvent systems, chlorobenzene (ink 1), chlorobenzene/o-dichlorobenzene (ink 2) and chlorobenzene/ tetrahydronaphthalene (ink 3), were compared as printable inks for the fabrication of polymer light-emitting diodes (PLEDs) using poly[2-methoxy-5-(2-ethylhexyl-oxyl)-1,4-phenylenevinylene (MEH-PPV) as an emissive material and an inkjet printer (Fujifilm Dimatix DMP-2831). Ink 1 clogged the printer’s nozzle and gave non-uniform film. Inks 2 and 3 were used to fabricate PLEDs with ITO/PEDOT:PSS/MEH-PPV/LiF/Al configurations. The best performance (turn-on voltage, 3.5 V; luminance efficiency, 0.17 cd/A; luminance, 1,800 cd/m) was obtained when ink 3 was used to form the emissive layer (thickness, 49 nm), attributable to the better morphology and suitable thickness of the MEH-PPV layer.

Two new small molecules, 5,5-bis(2-triphenylamino-3-decylthiophen-2-yl)-2,2-bithiazole ( M1 ) and 2,5-bis(2-triphenylamino-3-decylthiophen-2-yl)thiazolo[5,4-d]thiazole ( M2 ) based on an electron-donor triphenylamine unit and electron-acceptor thiophene–thiazolothiazole or thiophene–bithiazole units were synthesized by a palladium(0)-catalyzed Suzuki coupling reaction and examined as donor materials for application in organic solar cells. The small molecules had an absorption band in the range of 300–560 nm, with an optical band gap of 2.22 and 2.25 for M1 and M2 , respectively . As determined by cyclic voltammetry, the highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels of M1 were −5.27 eV and −3.05 eV, respectively, which were 0.05 eV and 0.02 eV greater than that of M2 . Photovoltaic properties of the small molecules were investigated by constructing bulk-heterojunction organic solar cell (OSC) devices using M1 and M2 as donors and fullerene derivatives, 6,6-phenyl-C61-butyric acid methyl ester (PC 61 BM) and 6,6-phenyl-C71-butyric acid methyl ester (PC 71 BM) as acceptors with the device architecture ITO/PEDOT:PSS/ M1 or M2 :PCBM/LiF/Al. The effect of the small molecule/fullerene weight ratio, active layer thickness, and processing solvent were carefully investigated to improve the performance of the OSCs. Under AM 1.5 G 100 mW/cm 2 illumination, the optimized OSC device with M1 and PC 71 BM at a weight ratio of 1:3 delivered a power conversion efficiency (PCE) of 1.30%, with a short circuit current of 4.63 mA/cm 2 , an open circuit voltage of 0.97 V, and a fill factor of 0.29. In contrast, M2 produced a better performance under identical device conditions. A PCE as high as 2.39% was recorded, with a short circuit current of 6.49 mA/cm 2 , an open circuit voltage of 0.94 V, and a fill factor of 0.39.

Highly efficient and cost-effective polymer solar cells (PSCs) based poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM) have been fabricated by inkjet-printing with various additives. All solution-processed layers in the solar cells—a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) layer and a photoactive layer based on P3HT and PCBM with additives—were inkjet-printed. The device performance is strongly influenced by the addition of high boiling point additives in the photoactive ink with chlorobenzene (CB) solvent. The morphology, optoelectronic properties, and overall solar cell performance of the devices were dramatically affected by additives, such as 1,8 octanedithiol (ODT), o-dichlorobenzene (ODCB) and chloronaphthalene (Cl-naph). A device fabricated from ink formulated with ODT exhibited the best overall performance with power conversion efficiency (PCE) of 3.71%.

In this article, we have demonstrated solar cell performance of the inkjet-printed PEDOT:PSS layer and the roles of additives in device efficiency. The newly proposed PEDOT:PSS inks with additives of glycerol and surfactant show the improved surface morphology and high conductivity resulting in the enhanced photovoltaic performance. Using the optimized ink formulation of PEDOT:PSS, we have demonstrated a 3.16% efficient solar cell with an inkjet printing.

Less-populated and well-isolated ZnO nanorods were prepared from a simple solution method by using polyethylene glycol (PEG) surfactant molecules. The structural and morphological information provided by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM) demonstrated the high purity of the ZnO nanorods that were free from any unknown impurities. Furthermore, annealing treatment was used to increase the length of the ZnO nanorods further at an elevated temperature. This ZnO was used as a buffer layer for polymer solar cells (PSCs) in the device configuration of ITO/ PEDOT:PSS/P3HT-PCBM/ZnO/Ag, in which the Ag cathode was prepared by the inkjet printing method using silver ink. The present study discusses and compares the performance of the devices with and without the ZnO buffer layer.

In an unprecedented attempt, we present an interesting approach of coupling solution processed ZnO planar nanorods (NRs) by an organic small molecule (SM) with a strong electron withdrawing cyano moiety and the carboxylic group as binding sites by a facile co-functionalization approach. Direct functionalization by SMs (SM-ZnO NRs) leads to higher aggregation owing to the weaker solubility of SMs in solutions of ZnO NRs dispersed in chlorobenzene (CB). A prior addition of organic 2-(2-methoxyethoxy)acetic acid (MEA) over ZnO NRs not only inhibits aggregation of SMs over ZnO NRs, but also provides enough sites for the SM to strongly couple with the ZnO NRs to yield transparent SM-MEA-ZnO NRs hybrids that exhibited excellent capability as electron transporting layers (ETLs) in inverted organic solar cells (iOSCs) of P3HT:PC60BM bulk-heterojunction (BHJ) photoactive layers. A strongly coupled SM-MEA-ZnO NR hybrid reduces the series resistance by enhancing the interfacial area and tunes the energy level alignment at the interface between the (indium-doped tin oxide, ITO) cathode and BHJ photoactive layers. A significant enhancement in power conversion efficiency (PCE) was achieved for iOSCs comprising ETLs of SM-MEA-ZnO NRs (3.64%) advancing from 0.9% for pristine ZnO NRs, while the iOSCs of aggregated SM-ZnO NRs ETL exhibited a much lower PCE of 2.6%, thus demonstrating the potential of the co-functionalization approach. The superiority of the co-functionalized SM-MEA-ZnO NRs ETL is also evident from the highest PCE of 7.38% obtained for the iOSCs comprising BHJ of PTB7-Th:PC60BM compared with extremely poor 0.05% for non-functionalized ZnO NRs.

Two new small molecules with a rigid planar naphtho[1,2-b:5,6-b']dithiophene (NDT) unit were designed and synthesized. Solution processed bulk-hetereojunction organic solar cells based on blends of the small molecules and [6,6]-phenyl-C(71)-butyric acid methyl ester (PC(71)BM) exhibited promising photovoltaic device performance with a maximum power conversion efficiency up to 2.20% under the illumination of AM 1.5G, 100 mW cm(-2).

Organic solar cells based on compound (IIIb) exhibit promising photovoltaic device performance with a maximum power conversion efficiency up to 2.20% under the illumination of AM 1.5G, 100 mW cm-2.

Zinc oxide (ZnO) was used as a buffer layer in the fabrication of polymer solar cells with the configuration of ITO/PEDOT:PSS/P3HT:PCBM/ZnO/Ag, in which the Ag cathode was prepared by inkjet printing using silver ink. Due to the hydrophobic nature of the P3HT:PCBM active layer surface, the hydrophilic silver ink cannot be coated directly on the top of the P3HT:PCBM layer. To overcome this problem, ZnO particles, prepared in a simple solution method by using polyethylene glycol (PEG) surfactant molecules, were used as a buffer layer between the P3HT:PCBM layer and Ag cathode. The present study discusses and compares the performance of the solar cells with and without the ZnO buffer layer.