Fabrication Of Polymer Solar Cells Research Articles

The impact of Ag/Co nanocomposite on organic charge transport medium for improved photocurrent in polymer solar cell

AbstractTuning charge transport properties using silver‐cobalt bimetallic nanoparticles is investigated to enhance the photo‐current collection in polymer solar cells. The silver‐cobalt nanoparticles were not only augmenting the charge transport processes but also expected to trap light by way of reflection. The polymers blend consisting of poly‐(3‐hexylthiophene) (P3HT):[6,6]‐phenyl C61 butyric acid methyl ester (PC61BM) is used in the fabrication of polymer solar cells. The experimental results indicated that the solar cells' performance depended on the concentration of Ag/Co in the hole transport layer (HTL). Nevertheless, the high‐power conversion efficiency value of up to 4.21% was observed, at the concentration of 0.1% by weight, which is much higher than pristine solar cells due to improved measured photocurrents from the devices. This is a significant improvement in PCE by 66.4% compared to the undoped transport medium. Ag/Co nanocomposite is found to be more stable under ambient laboratory conditions.

High transparency and performance slot‐die‐coated large‐area polymer solar module

AbstractWe fabricate polymer solar cells (PSCs) and modules by sheet‐to‐sheet slot‐die coating under air environment based on halogen‐free host solvent. How to upscale small‐area PSC to large‐area PSC module is demonstrated here. The opaque module exhibits the most superior performance among the slot‐die‐coated modules reported. The scaling of both the semitransparent top electrode and PSC module is a challenge due to the complex difficulties. In this study, the semitransparent MoO3/Ag/MoO3 top electrode is successfully upscaled to be in the large‐area semitransparent PSC module. Ag layer thickness as reflector in the tri‐layer electrode is used to tune the trade‐off between transmittance, conductivity, and the light absorption in the active layer. The matching combination of transmittance, absorption spectra of MoO3/Ag/MoO3 top electrode, and active layer is a main key of our approach greatly improving photovoltaic and optical performance. The power conversion efficiencies (PCEs) of the semitransparent PSC modules with Ag thickness of 25, 20, and 15 nm are 7.1%, 5.9%, and 4.4%, respectively. The corresponding average visible transmittance (AVT) values are 20.5%, 28.3%, and 36.1%, respectively. The transmittance values at 550 nm are ranging from 24% to 40%. According to the review of all the reported semitransparent modules (>10 cm2), our modules demonstrate the excellent trade‐off performance about two times better than the large‐area semitransparent PSC modules currently reported either based on the similar PCEs or AVTs.

Photovoltaic performances of two alternating polymers having meta-octyloxy-phenyl modified dithieno[3,2-f:2′,3′-h]quinoxaline unit

Two donor-acceptor (D-A)-type alternative conjugated polymers, namely Z2 and Z3, based on meta-octyloxy-phenyl modified dithieno[3,2-f:2′,3′-h]quinoxaline segment as the electron-deficient unit, thiophene and 2,3-dioctylthienyl substituted benzo[1,2-b:4,5-b’]dithiophene as the electron-giving segment were synthesized, which were used as donors to fabricate polymer solar cells (PSCs) with a small molecule electron-acceptor material i-IEICO-4F. With wide-bandgaps of 1.95 eV for Z2 and 2.02 eV for Z3, both of the two polymers provide complementary absorption with i-IEICO-4F. Moreover, Z3 shows deepened molecular frontier orbitals compared to Z2. Polymer solar cells based on Z2 and i-IEICO-4F acquired a moderate efficiency of 6.46%. While the device of Z3:i-IEICO-4F possessed exhibited better charge acquisition and generation properties, suppressed charge recombination probability, higher and more balanced hole and electron mobilities, and superior molecular orientation and crystallinity, thus achieving simultaneously improved short-circuit current density (JSC, 16.76 mA cm−2), VOC (0.936 V), fill factor (FF, 53.93%), and the resultant high PCE (8.46%). This work is of great significance for obtaining highly efficient PSCs with alkyoxy-phenyl modified dithieno[3,2-f:2′,3′-h]quinoxaline unit as the electron-attractive fused-ring core in wide bandgap polymers.

Electrochemical deposition of NiO bunsenite nanostructures with different morphologies as the hole transport layer in polymer solar cells

• Electrodeposition of p-type nickel oxide (NiO) using anodic potentiostatic and cyclic voltammetry. • Applying both NiO as the hole transport layer (HTL) in the fabrication of polymer solar cells. • NiO synthesized by the anodic potentiostatic exhibited the best features as the HTL. • The best PSC showed J SC , V OC , FF , and PCE of 10.95 mA/cm 2 , 0.64 V, 0.60 and 4.21%, respectively. Hole transport layers (HTLs) are one of the most important components of bulk heterojunction polymer solar cells (BHJ PSCs), having functions of optimizing interface, adjusting the energy match, and helping obtain higher PCE. Inorganic p-type semiconductors are alternative HTLs due to their chemical stability, high mobility, high transparency, and applicable valence band (VB) energy level. In this work, interlayer engineering in BHJ PSC was performed using solution-processed p-type nickel oxide (NiO) as the HTL. NiO nanostructures were synthesized by anodic potentiostatic and cyclic voltammetry (CV) electrodeposition methods. Simple adjustment of the applied potential regime and electrodeposition parameters led to considerable structural and electrochemical changes in the resulting NiO. Eventually, the best sample was selected in terms of suitable surface conductivity, high optical transparency, and appropriate energy levels. NiO nanostructures with FCC crystal structure synthesized by anodic potentiostatic electrodeposition showed conductivity of 0.038 mS.cm -1 and charge mobility of 2.01 cm 2 .V -1 s -1 , respectively, about 30.2% and 24.8% higher than the NiO synthesized by CV. The anodic potentiostatic electrodeposition method increased the photovoltaic performance of the PSCs by 43% compared to the CV method. The average power conversion efficiencies for the anodic potentiostatic and CV methods were 2.95% and 4.21%, respectively. The PCE of these cells was about 13% and 62% higher than that considered for the reference device prepared based on the PEDOT:PSS HTL.

Flash‐Lamp Processing of Charge Extraction Layers for Polymer Solar Cells

AbstractThermal annealing (TA) is one of the most used processing techniques for the fabrication of polymer solar cells. The method is not only used to dry solution‐processed films but also for improving the electrical conductivity and the optical absorption of the materials after coating as films. Its use is questionable in combination with high throughput manufacturing techniques such as roll‐to‐roll large‐scale production since annealing times of several minutes already put up high demands on oven lengths. Furthermore, the commonly used flexible substrates are not compatible with high processing temperatures. Therefore, there is a need for more rapid treatment techniques, which do not negatively affect the plastic substrate. Herein, it is successfully demonstrated that flash lamp annealing (FLA) can be a valid alternative to TA. The FLA technique is applied at various pulse durations and thus energy doses to PEDOT:PSS and SnO2 films used as charge extraction layers in conventional and inverted solar cells architectures. In combination with PM6:Y6 photoactive layer, the obtained device's performances are comparable or even better than the devices treated with the classical TA on a hotplate. In terms of energy efficiency, the FLA is clearly more efficient than the TA, even at the size of prototypes.

Wide‐Bandgap Donor–Acceptor Copolymer Based on BDTTz Donor and TPD Acceptor for Polymer Solar Cells Using Fullerene and Nonfullerene Acceptors

A donor–acceptor copolymer based on thiazole substituted benzodithiophene (BDTTz) (donor unit) and thieno[3,4‐c]pyrrole‐4‐6‐dione (TPD) (acceptor unit) P(BDTTz‐TPD) denoted as P132 is investigated. P132 shows an absorption profile from 300 to 680 nm and the low‐lying highest occupied molecular orbital (HOMO) energy level of −5.54 eV. P132 as donor along with fullerene derivative (PC71BM) or nonfullerene denoted as BThIND‐Cl as acceptor are used for the fabrication of polymer solar cells. The P132:BThIND‐Cl‐based polymer solar cell shows high open‐circuit voltage as compared with P132:PC71BM which is attributed to the upshifted lowest unoccupied molecular orbital level of BThIND‐Cl and low energy loss. Moreover, P132:BThIND‐Cl attains higher short‐circuit current than that for P132:PC71BM which is attributed to the broader absorption spectra and low optical band gap of BThIND‐Cl, which leads to high light‐harvesting ability of the P132:BThIND‐Cl active layer. The polymer solar cells based on P132:PC71BM and P132:BThIND‐Cl attain power conversion efficiencies of 7.03% and 15.52%, respectively. The charge transport is more balanced in P132:BThIND‐Cl and results in a high value of fill factor. Small energy loss in P132:BThIND‐Cl‐based PSCs is attributed to the low HOMO offsets between P132 and BThIND‐Cl.

Non-halogenated solvent processable wide bandgap polymer based on carboxylate-substituted benzodithiophene for high-efficiency polymer solar cells

The use of non-halogenated solvents for the fabrication of polymer solar cells (PSCs) is a crucial step for commercial applications in the future. Herein, we synthesize a wide bandgap polymer PBDT-ST with alkylthio chains substituted benzodithiophene (BDT) as donor unit and carboxylate-substituted BDT as acceptor unit. The polymer PBDT-ST possesses a wide bandgap over 1.90 eV and a deep highest occupied molecular orbitals (HOMO) levels below −5.50 eV, which is beneficial to obtain a high open circuit voltage (Voc). In addition, PBDT-ST shows good solubility in halogenated and non-halogenated solvents. The o-xylene processed PBDT-ST:ITIC-2F blend film exhibits improved molecular order, film morphology and charge mobilities compared with o-dichlorobenzene (o-DCB) processed one. As the results, the o-DCB processed PBDT-ST:ITIC-2F based device can achieve a power conversion efficiency (PCE) of 10.48%. When the non-halogenated o-xylene as solvents and non-halogenated diphenyl ether (DPE) as additive, an improved PCE of 11.14% can be obtained with Voc of 0.90 V, Jsc of 17.83 mA/cm2 and FF of 69.36%. Our research indicates that carboxylate-substituted BDT based polymer PBDT-ST as a promising wide bandgap donor material can achieve excellent photovoltaic performance for PSCs processed by non-halogenated solvent.

Influence of the dipole moment on the photovoltaic performance of polymer solar cells employing non-fullerene small molecule acceptor

A new narrow bandgap non-fullerene acceptor with a DPP core and dicyanorhodanine terminals linked by selenophene spacers has been synthesized. Optical and electrochemical properties of MPU5 were examined and compared to that of its comparable MPU2, which contains thiophene linkers instead of selenophene. MPU5 has a lower optical bandgap (1.38 eV) than MPU2 (1.41 eV), this may be due to the higher electron richness and lower aromatici character of selenophene, comparative to thiophene, favoring a quinoidal structure and intramolecular charge transfer between push–pull moieties. MPU5 was employed as the electron acceptor in conjunction with a conjugated polymer (PCDTBT) as donor with a complementary absorption (350–650 nm) and high HOMO and low LUMO energy levels (–5.4 eV and –3.6 eV, respectively) for the fabrication of polymer solar cells using a bulk heterojunction active layer. The MPU5-based polymer solar cell enabled an overall power conversion efficiency (PCE) of 10.10% with an Eloss of 0.43 eV with an optimized bulk heterojunction active layer. These values are better than those for the MPU2 counterpart (PCE = 8.04%, Eloss = 0.56 eV). The higher PCE obtained for the MPU5-based polymer can be correlated with better balanced charge transport, appropriate active layer nanoscale morphology, efficient charge extraction and longer charge carrier lifetime, resulting in an improvement in the Jsc and FF values. The superior Voc value for the MPU5-based polymer may be related to the lower energy loss caused by the larger dipole moment and dielectric constant of MPU5, which result in a smaller exciton binding energy in the active layer.

Eco-Friendly Polymer Solar Cells: Advances in Green-Solvent Processing and Material Design.

Despite the recent breakthroughs of polymer solar cells (PSCs) exhibiting a power conversion efficiency of over 17%, toxic and hazardous organic solvents such as chloroform and chlorobenzene are still commonly used in their fabrication, which impedes the practical application of PSCs. Thus, the development of eco-friendly processing methods suitable for industrial-scale production is now considered an imperative research focus. This Review provides a roadmap for the design of efficient photoactive materials that are compatible with non-halogenated green solvents (e.g., xylenes, toluene, and tetrahydrofuran). We summarize the recent development of green processing solvents and the processing methods to match with the efficient photoactive materials used in non-fullerene solar cells. We further review progress in the use of more eco-friendly solvents (i.e., water or alcohol) for achieving truly sustainable and eco-friendly PSC fabrication. For example, the concept of water- or alcohol-dispersed nanoparticles made of conjugated materials is introduced. Also, recent important progress and strategies to develop water/alcohol-soluble photoactive materials that completely eliminate the use of conventional toxic solvents are discussed. Finally, we provide our perspectives on the challenges facing the current green processing methods and materials, such as large-area coating techniques and long-term stability. We believe this Review will inform the development of PSCs that are truly clean and renewable energy sources.

Novel benzo[1,2-b:4,5-b']difuran-based copolymer enables efficient polymer solar cells with small energy loss and high VOC

Abstract Benzo[1,2-b:4,5-b']difuran (BDF)-based copolymers have displayed some success in fabricating efficient polymer solar cells (PSCs). However, the PSCs suffer from significant energy loss (Eloss) that results in low open-circuit voltage (Voc) and greatly hinders the further improvement of photovoltaic performance of PSCs. Herein, we designed and synthesized a novel copolymer PBDFP-Bz based on BDF and benzotriazole, where the BDF unit was modified by (2-ethylhexyl)(2-fluorophenyl)sulfane side chain. PBDFP-Bz displays large coplanar structure and deep-lying highest occupied molecular orbital energy level of −5.50 eV. PSCs based on PBDFP-Bz as donor and small molecule ITIC as acceptor achieved a power conversion efficiency (PCE) of 11.10% with Voc of 0.97 V and Eloss of 0.60 eV. Moreover, when adopting small molecule IT-M to replace ITIC, PBDFP-Bz:IT-M based PSCs delivered a larger Voc of 1.02 V and a smaller Eloss of 0.57 eV due to the shallower lowest unoccupied molecular orbital energy level of IT-M versus that of ITIC. Importantly, a remarkable PCE of 12.93% was also obtained for PBDFP-Bz:IT-M based PSCs, which is among attractive photovoltaic performance of PSCs containing BDF-based copolymers. Our work not only suggests that PBDFP-Bz is a promising copolymer for efficient PSCs fabrication, but also sheds light on the design rule that managing the molecular structure of photovoltaic material and its energy level is an effective strategy to fabricate highly efficient PSCs.

Using Dual Microresonant Cavity and Plasmonic Effects to Enhance the Photovoltaic Efficiency of Flexible Polymer Solar Cells.

Fabricating polymer solar cells (PSCs) on flexible polymer substrates, instead of on hard glass, is attractive for implementing the advantage and uniqueness of the PSCs represented by mechanically rollable and light-weight natures. However, simultaneously achieving reliable robustness and high-power conversion efficiency (PCE) in such flexible PSCs is still technically challenging due to poor light harvesting of thin photoactive polymers. In this work, we report a facile, effective strategy for improving the light-harvesting performance of flexible PSCs without sacrificing rollability. Very high transparent (93.67% in 400–800 nm) and low sheet resistance (~10 Ω sq−1) ZnO/Ag(O)/ZnO electrodes were implemented as the flexible substrates. In systematically comparison with ZnO/Ag/ZnO electrodes, small amount of oxygen induced continuous metallic films with lower thickness, which resulted in higher transmittance and lower sheet resistance. To increase the light absorption of thin active layer (maintain the high rollability of active layer), a unique platform simultaneously utilizing both a transparent electrode configuration based on an ultrathin oxygen-doped Ag, Ag(O), and film and plasmonic Ag@SiO2 nanoparticles were designed for fully leveraging the advantages of duel microresonant cavity and plasmonic effects to enhance light absorbance in photoactive polymers. A combination of the ZnO/Ag(O)/ZnO electrode and Ag@SiO2 nanoparticles significantly increased the short-current density of PSCs to 17.98 mA cm−2 with enhancing the photoluminescence of PTB7-Th film. The flexible PSC using the optimized configuration provided an average PCE of 8.04% for flexible PSCs, which was increased by 36.27% compared to that of the PSC merely using a conventional transparent indium tin oxide electrode.

ZnO/Ag/ZnO multilayer transparent electrode for highly-efficient ITO-Free polymer solar cells

Ultrathin metal film (UTMF) with a ZnO/Ag/ZnO hybrid structure was used as transparent electrode in a high-efficiency bulk heterojunction system for the fabrication of ITO-free polymer solar cells. The performance of the devices was carefully tuned through optical simulation using transfer matrix method by varying the thickness of ZnO seed layer and thin absorber layer. By employing appropriate device architecture, polymer solar cells fabricated using this UTMF-based electrode show efficiency as high as 9.49%, which is slightly higher compared to that of ITO-based device. From good agreement between the external quantum efficiency and optical modeling, it was found that the optimized microcavity configuration formed in UTMF-based device can greatly enhance the absorbance of the BHJ layer at longer wavelength as well as the favored exciton distribution for better charge transport and collection.

Nd:YAG pulsed laser production of reduced-graphene oxide as hole transporting layer in polymer solar cells and the influences of solvent type

Abstract Graphene oxide (GO) was reduced using 532 nm Nd:YAG pulsed laser irradiation (unfocused, 10 Hz repetition rate, 0.3 J/cm2) in different solvents including water, ethanol and formic acid. The obtained reduced GOs (r-GOs) were employed as hole transporting layers (HTLs) in fabrication of polymer solar cells (PSCs). The changes in the chemical composition, phase purity, optical properties, level of defects, sheet resistance (Rsh), charge transfer resistance (Rct) and morphology of r-GOs were systematically investigated using Fourier transform infrared spectroscopy, x-ray diffraction, UV–Vis and Raman spectroscopy, four-point probe, electrochemical impedance spectroscopy and atomic force microscopy. Results revealed that laser reduction of GO in formic acid led to formation of r-GOs with superior physicochemical and electrochemical characteristics, implying higher hole scavenging ability of formic acid compared to water and ethanol. The r-GOs prepared in formic acid appeared to have the lowest Rsh, Rct and surface roughness. This was attributed to the higher elimination of oxygenated functional groups in formic acid, confirmed by results obtained from physicochemical characterization of the prepared samples. Comparing the photovoltaic parameters of PSCs prepared based on r-GOs as HTL revealed that the r-GO sample produced in formic acid can act as a better HTL in P3HT:PCBM-based PSCs. This cell exhibited the highest short circuit current density (10.15 mA) and power conversion efficiency (4.02%), which was about 22% higher than that achieved for the reference PSC prepared using PEDOT:PSS as HTL. Results suggest that pulsed laser production can be considered as a promising method to produce r-GOs possessing appropriate characteristics as HTL in PSCs.

Indolo[3,2‐b]carbazole‐based poly(arylene ethynylene)s through Sonogashira coupling for optoelectronic and sensing applications

ABSTRACTTwo indolo[3,2‐b]carbazole (ICZ)‐based polymers have been designed and synthesized using Sonogashira cross‐coupling based on dibromoindolo[3,2‐b]carbazoles and 2,7‐diethynylfluorene or 9,10‐diethynylanthracene. The 2, 8 positions of the ICZ moiety has been used for the bridging of arylene ethynylene structure to form the polymer backbone. The characterization has been done by Fourier transform infrared, proton nuclear magnetic resonance, ultraviolet–visible and (UV–vis) fluorescence spectroscopic methods. The polymers, moderately soluble in aprotic and chlorinated solvents, have been found to possess thermal stability above 300°C. The band gap examinations, executed through cyclic voltammetry and complemented by UV–vis studies, indicated their semiconducting nature and the possibility for their utilization for the fabrication of polymer solar cells and for optical switching applications. Interestingly, the new diethynylindolocarbazole systems have been found to act as Bronsted acid sensors as well as a Hg2+ receptors. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 46940

Aqueous Soluble Fullerene Acceptors for Efficient Eco-Friendly Polymer Solar Cells Processed from Benign Ethanol/Water Mixtures

We present a new series of fullerene derivatives that exhibit solubility in ethanol/water solvent mixtures and implement these materials to fabricate polymer solar cells (PSCs) using environmentally benign solvents. In order to simultaneously optimize the processability of the fullerenes in ethanol/water solvent mixtures and device performance, different fullerene mono-adducts were designed by introducing oligoethylene glycol side chains with different lengths and number of branches. As a result, we achieved power conversion efficiencies up to 1.4% for PSCs processed from benign ethanol/water mixtures in air. Significantly, the new alcohol/water-soluble fullerene derivatives displayed electron mobilities up to 1.30 × 10–4 cm2 V–1 s–1, 150 times higher than those of a previously reported alcohol-soluble fullerene bis-adduct, owing to efficient packing of the fullerenes. Femtosecond transient absorption spectroscopy revealed the acceptor side chain to markedly impact geminate and/or nongeminate charge recom...

Research progress in high efficiency thick film polymer solar cells

Polymer solar cells (PSCs) are considered as the most promising third-generation photovoltaic technology in the future due to their advantages such as light weight, thin film and flexibility. Nowadays, the power conversion efficiencies (PCE) of PSCs have pasted 13%, laying the foundation for their fab-scale production. To realize the scalable fabrication of PSCs, the key issue is developing high efficiency thick film PSCs compatibility to the roll-to-roll (R2R) printing process. In this article, different kinds of high efficiency thick film PSCs including fullerene PSCs, non-fullerene PSCs and ternary PSCs are reviewed according to the recent research progress. The relevant research works on the molecular design of donor and acceptor materials, morphology of photoactive layers, fabrication method and mechanism of solar cells devices are discussed. And the future prospect of the research on thick film PSCs is presented.

The influence of ionic radius of interfacial molecule on device performances of polymer solar cells

Ionic radius of interfacial molecular can affect the interface property and key electron transfer processes occurring at interface in polymer solar cells. To study the effects of different ionic radius of electron transfer layer on device performances, we introduce various stearate salts (Na+, K+ and Cs+) as electron transfer layer to fabricate polymer solar cells. Interestingly, it is found that the key device parameters such as Voc, Jsc, fill factor and PCE of polymer solar cells present regular change with the ionic radius increasing. We systematically study the effects of different ionic radius of electron transfer layer on the various parameters of polymer solar cells and believe this regularity paves a way for further understanding and improving the performances of polymer solar cells.

Non-fullerene acceptors end-capped with an extended conjugation group for efficient polymer solar cells

We report two novel small-molecule non-fullerene acceptors, IF-TN and IDT-TN, with indenofluorene (IF) and indacenodithiophene (IDT) as their respective central electron-rich cores and naphthyl-fused indanone (N) as the electron-withdrawing end-groups. By pairing these non-fullerene acceptors with a widely used polymer PBDB-T, the fabricated polymer solar cells based on PBDB-T:IDT-TN obtain a power conversion efficiency up to 5.89%, associated with a relatively high open-circuit voltage of 0.97 V and a remarkably low non-radiative open-circuit voltage loss of 0.23 V. These findings provide an effective approach for the rational molecular design of small-molecule acceptors with low non-radiative open-circuit voltage loss.

Effect of Benzene Rings’ Incorporation on Photovoltaic Performance of Indacenodithiophene‐cored Molecular Acceptors

Two simple molecular acceptors, NIDBT and NIDT, bearing the same end groups of 2‐(3‐oxo‐2,3‐dihydro‐1H‐inden‐1‐ylidene)malononitrile (INCN) yet with different core units, indenofluorenodithiophene (IDBT) and indaceno[2,1‐b:6,5‐b’]dithiophene (IDT), respectively, were adopted to fabricate polymer solar cells by blending with a narrow bandgap polymer donor, PBDBTBTT‐Hex (P3). The incorporation of benzene rings into the molecular skeletons generates a negative effect on the photovoltaic performance of resultant molecular acceptor, rendering an inferior power conversion efficiency of 2.45%, compared to 4.05% for the NIDT‐based bulk‐heterojunction solar cells. Detailed comparison on photovoltaic parameters indicates that the fusion by incorporating two separated benzene rings into the IDT core renders molecular acceptor of weakened intermolecular interaction with the polymer donor, which results in over‐aggregated phase separation, unbalanced charge transport, and serious recombination within the photovoltaic devices. The work contributes to a deep understanding of the effect of skeleton‐fusion strategy for designing high‐performance molecular acceptors.

Toward Enhancing Solar Cell Performance: An Effective and "Green" Additive.

Performance of bulk heterojunction polymer solar cells (PSCs) highly relies on the morphology of the photoactive layer involving conjugated polymers and fullerene derivatives as donors and acceptors, respectively. Herein, butylamine was found to be able to optimize the morphology of the donor/acceptor (D/A) film composed of a blend of poly(3-hexylthiophene-2,5-diyl) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM). Compared to the commonly used alkane dithiols and halogenated additives with high boiling points, butylamine has a much lower boiling point between 77 and 79 °C, and it is also much "greener". A specific interaction between butylamine and PCBM was demonstrated to account for the morphology improvement. Essentially, butylamine can selectively dissolve PCBM in the P3HT:PCBM blend and facilitate the diffusion of PCBM in the film fabrication processes. Atomic force microscopy and X-ray photoelectron spectroscopy investigations confirmed the formation of the P3HT-enriched top surface and the abundance of PCBM at the bottom side, i.e., the formation of vertical phase segregation, as a consequence of the specific PCBM-butylamine interaction. The D/A film with inhomogeneously distributed D and A components in the vertical film direction, with more P3HT at the hole extraction side and more PCBM at the electron extraction side, enables more efficient charge extraction in the D/A film, reflected by the largely enhanced fill factor. The power conversion efficiency of devices reached 4.03 and 4.61%, respectively, depending on the thickness of the D/A film, and these are among the best values reported for P3HT:PCBM-based devices. As compared to the devices fabricated without the introduction of butylamine under otherwise the same processing conditions, they represented 19.6 and 21.6% improvement in the efficiency, respectively. The discovery of butylamine as a new, effective additive in enhancing the performance of PSCs strongly suggests that the differential affinity of additives toward donors and acceptors likely plays a more important role in morphology optimization than their boiling point, different from what was reported previously. The finding provides useful information for realizing large-area PSC fabrication, where a "greener" additive is always preferred.