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Comprehensive Summary: Constructing monolithic tandem solar cells (TSCs) is an effective method to break the Shockley–Queisser (S–Q) radiative efficiency limit for single‐junction solar cells. Employing the wide bandgap perovskite materials and low bandgap organic materials as absorber layers for front and rear subcells, respectively, to construct perovskite/organic TSCs can complementarily absorb sunlight in ultraviolet‐visible (UV‐Vis) range by front perovskite and near‐infrared (NIR) range by rear organic molecules, thus reducing the thermalization energy losses. Besides the subcells, the interconnection layer (ICL), which physically and electrically connects the front and rear subcells, is also an important tunnel junction to recombine charges. In this review, we summarize the optimization strategies of wide bandgap perovskites for front subcell, narrow bandgap organic material for rear subcell, and the ICLs employed in monolithic perovskite/organic TSCs. [ABSTRACT FROM AUTHOR]

Semitransparent organic solar cells (ST‐OSCs) with vivid colors offer attractive prospects in aesthetical power‐generating windows. Unfortunately, they still suffer from certain limitations since the common approach for generating different colors is to adopt various photoactive layers, which complicates production processes and results in process‐induced performance deviations. Additionally, efficient ST‐OSCs with simultaneously improved average visible transmittance (AVT) and color rendering index (CRI) remain still challenging due to the trade‐off between photoelectric conversion efficiency (PCE) and AVT besides the interdependent/interactive relations of AVT and CRI. Herein, Ag/MoO3/Ag microcavity structure is introduced to delicately tune the absorption spectra of PM6:Y6 active material. The Ag/MoO3/Ag microcavity endows freely tunable colors to devices and meanwhile functions as a hole‐collecting layer. Under the guidance of optical simulation, the rationally designed ST‐OSCs with Ag/MoO3/Ag microcavity and Hf(ACB1)4 electron collection layer display good eye comfort colors (purple, sky blue, cyan, green, and magenta) independently of the inherent color of PM6:Y6 active material, and show a close to 12% PCE with an AVT of 23.69% and a CRI of 92.5 for cyan devices. This work provides a practical way for achieving efficient ST‐OSCs with simultaneously improved AVT and CRI, and using them in building‐integrated photovoltaics as multicolored photovoltaic glass windows. [ABSTRACT FROM AUTHOR]

Abstract: Ternary polymer solar cells (PSCs) based on multiple materials with level matching and complementary absorptions are regarded as an efficient way to overcome the light‐harvesting restriction to surpass high‐performance binary PSCs. This study introduces the third component, nonfullerene acceptor IEICO, into binary PSC‐based PBDTBDD:PC71BM to fabricate ternary PSC with one donor and two acceptors. By carefully tuning the third component ratio and cathode engineering, the resulting ternary PSC shows a power conversion efficiency of 10.51%, greatly improved in comparison with binary PSCs‐based PBDTBDD:PC71BM (7.86%) and PBDTBDD:IEICO (5.19%). In addition to extended light absorption, the third component IEICO could accelerate charge‐carrier transfer, decrease charge recombination, and increase electron collection, resulting from cascade energy levels, and ameliorate the device morphology to increase the contact area of the active layer and cathode buffer layer. This work demonstrates that ternary PSC incorporated with IEICO is a promising structure for producing high performance PSCs. [ABSTRACT FROM AUTHOR]

New breakthroughs are expecting to be achieved based on the discovery of novel interfacial materials for polymer solar cells (PSCs). Herein, the simple and facial approach of spin-coating technology with post heat and ultraviolet-ozone treatment is performed on niobium oxalate to prepare Nb 2 O 5 interfacial layer with ultra-high transmittance. The ultraviolet photoemission spectroscopy results confirm that Nb 2 O 5 with a work function of 4.85 eV is suitable for employing as anode buffer layer (ABL). The average power conversion efficiencies (PCEs) of the P3HT:PCBM-based fullerene devices with Nb 2 O 5 ABL reaches to 4.01%, surpassing that (3.69%) of the control devices with ITO/PEDOT:PSS ABL. Further investigations on the PBDB-T:ITIC-based non-fullerene PSCs with Nb 2 O 5 ABL demonstrate that a PCE as high as 8.67% can be reached, which is superior to that of device modified by PEDOT:PSS ABL (8.03%). Namely, 8% efficiency improvement in PSCs based on fullerene and non-fullerene acceptors realized as compared to the control devices with PEDOT:PSS ABL. [ABSTRACT FROM AUTHOR]

The photon harvesting of the photoactive layer within a multilayered polymer solar cells (PSCs) greatly affects the output electric power of the devices. For PSCs, the device performance is very sensitive to the photoactive layer thickness. Therefore, how to enhance the light absorption of the photoactive film with fixed thickness is still a big challenge. Plasmonic enhancement induced by noble metal nanoparticles has been proved to be an effective way to enhance light trapping inside the photoactive film without increasing the thickness of film. By incorporating Au decahedra into the poly(3,4-ethylenedioxythiophene): poly(4-styrenesulfonate) (PEDOT:PSS) anode buffer layer, high performance plasmonic PSCs based on P3HT:PC 60 BM and PBDT-TS1:PC 70 BM were fabricated and the light response of the PSCs are greatly improved in a broadband wavelength, resulting in a remarkable enhancement in short-circuit current density. The calculation results of finite difference time domain (FDTD) confirm that the plasmonic effects induce enhancement in device performance. Upon optimization, the best power conversion efficiency (PCE) of the device based on P3HT:PC 60 BM and PBDT-TS1:PC 70 BM reaches 4.14% and 10.29%, respectively, among the best values reported in literature. These results can provide valuable guidelines for the design of metal nanostructures for organic photovoltaic applications. [ABSTRACT FROM AUTHOR]

High efficiency polymer solar cells using solution processed s‐ReOx as the anode buffer layer are demonstrated. The s‐ReOx layer can effectively change the light distribution within the photoactive layer and enhance its absorption. The solution‐processable s‐ReOx is a promising anode buffer layer material for high performance PSCs [ABSTRACT FROM AUTHOR]

ABSTRACT Novel bromine-functionalized photocrosslinkable low-bandgap copolymers, PBDTTT-Br25 and PBDTTT-Br50, are synthesized via Stille cross-coupling polymerization for the purpose of stabilizing the film morphology in polymer solar cells (PSCs). Photocrosslinking of PBDTTT-Br25 and PBDTTT-Br50 copolymers dramatically improves the solvent resistance of the active layer without disrupting the molecular ordering and charge transport, which is confirmed by the insolubility of the films washed by organic solvents and by their thermal behavior. As a result, the formation of large aggregations of fullerene is suppressed in polymer:fullerene blend films even after prolonged thermal annealing, and the stability of the device is enhanced when compared with cells based on noncrosslinkable PBDTTT. The power conversion efficiency of the PSCs based on PBDTTT-Br25 and PBDTTT-Br50 reaches 5.17% and 4.48%, respectively, which is improved obviously in comparison with that (4.26%) of the PSCs based on the control polymer PBDTTT. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3123-3131 [ABSTRACT FROM AUTHOR]

We report polymer solar cells (PSCs) based on poly(3-hexylthiophene (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) using water-soluble nickel acetate (Ni(CH3COO)2, NiAc) instead of acidic poly(3,4-ethylenedioxythiophene) : poly(styrenesulfonate) (PEDOT : PSS) as hole collection layer (HCL) between the indium tin oxide (ITO) electrode and photoactive layer. The NiAc layer can effectively decrease Rs and increase Rp and shows effective hole collection property. Under the illumination of AM1.5G, 100 mW/cm2, the short-circuit current density ( Jsc) of the NiAc based device (ITO/NiAc/P3HT : PCBM/Ca/Al) reach 11.36 mA/cm2, which is increased by 11% in comparison with that (10.19 mA/cm2) of PEDOT : PSS based device (ITO/PEDOT : PSS/P3HT : PCBM/Ca/Al). The power conversion efficiency of the NiAc based devices reach 3.76%, which is comparable to that (3.77%) of the device with PEDOT : PSS HCL under the same experimental conditions. Moreover, NiAc based PSCs show superior long-term stability than PEDOT : PSS based PSCs. Our work gives a new option for HCL selection in designing more stable PSCs. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 [ABSTRACT FROM AUTHOR]

Abstract: We demonstrate efficient polymer solar cells (PSCs) based on poly(3-hexylthiophene) (P3HT) and fullerene derivatives ether Indene-C60 Bisadduct (IC60BA) or Indene-C70 Bisadduct (IC70BA)) by using solution-processed titanium(IV) oxide bis(2,4-pentanedionate) (TOPD) as electron collection layer (ECL) between the Al cathode and photoactive layer. The TOPD buffer layer was simply prepared by spin-coating isopropanol solution of TOPD on active layer and then baked at 80°C for 15min. The short-circuit current density (Jsc ) and the open-circuit voltage (Voc ) of the devices can be simultaneously and significantly improved by optimizing the electron collection layer, the photoactive layer and the device fabrication conditions. The power conversion efficiency (PCE) of the P3HT:IC60BA BHJ device with TOPD buffer layer reaches 5.0% under the illumination of AM1.5G, 100mW/cm2, which is increased by 27% in comparison with that (3.9%) of the device without TOPD buffer layer under the same experimental conditions. When IC70BA was chosen instead of IC60BA, the BHJ device could show better performance with PCE of 5.59%. The results indicate that TOPD is a promising electron collection layer for PSCs. [Copyright &y& Elsevier]

Abstract: We demonstrate efficient inverted polymer solar cells (PSCs) based on poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) by using solution-processed titanium(IV) oxide bis(2,4-pentanedionate) (TOPD) as electron collection layer (ECL) between the indium tin oxide (ITO) electrode and photoactive layer. The TOPD buffer layer was prepared by spin-coating isopropanol solution of TOPD on ITO and then baked at 140°C for 5min. The power conversion efficiency (PCE) of the inverted PSC with TOPD buffer layer reaches 4% under the illumination of AM1.5G, 100mW/cm2, which is increased by 76% in comparison with that (2.27%) of the inverted device without TOPD ECL. The results indicate that TOPD is a promising electron collection layer for inverted PSCs. [Copyright &y& Elsevier]

Unbalanced photocurrent output for each sub-cell in monolithic multiple junction solar cells (MMJ-SCs) reduces the achievable photovoltaic power efficiency (PCE). Here, we first introduce Au decahedra nanoparticles to realize the plasmon-enhanced photo-absorption of GaInP top-cell and achieve the current-matched MMJ-SCs. By simply spin-coating the Au decahedral nanoparticles on the illuminated surface of the devices, the PCEs of the monolithic double junction and triple junction solar cells increase significantly from 27.01% to 28.63% and from 29.88% to 31.90%, respectively. Both the theoretical local electromagnetic distributions and the experimental extinction properties confirm the plasmonic induced absorption enhancement in device performance, and further elucidate the essential reason for photocurrent enhancement derives from the more furious oscillation of free electrons in the vicinity of sharp vertexes for Au decahedra nanoparticles. Our results demonstrate that Au decahedra with sharp vertexes and edges are promising for meliorating the trade-off between light absorption and carrier collection in GaInP top-cell. In addition, this facile and simple strategy also highlights non-annealing treatment and prevents the impurity diffusion at high temperature for MMJ-SCs, and may facilitate other types of solar-harvesting devices. [ABSTRACT FROM AUTHOR]

• Theoretical analysis indicates lower binding energy (E b) can reduce the V oc loss. • A theoretical PCE of 18.86% was obtained via optimizing the E b values. • PM6:Y6 film with a 0.14 eV E b was achieved via optimizing the CN concentration. • PM6:Y6-based devices with a 0.14 eV E b reach a PCE of 16.14%. • Short electron-hole pair binding distances (a) can further reduce V oc losses. The energy loss during exciton dissociation is one of key reasons for organic solar cells (OSCs) with inferior performance. Herein, a theoretical and experimental guidance for highly efficient OSCs with outstanding exciton dissociation rate is introduced via fine-tuning the binding energy (E b) and the electron-hole pair binding distance (a) in the charge transfer (CT) state. Results suggest that decreasing the E b appropriately is favorable for higher photovoltaic conversion efficiency (PCE). Hence, we attempt to modulate the E b of PM6:Y6 photoactive layer by changing additive and their corresponding concentration. Investigations show that the E b of PM6:Y6 changes slightly with different additives, and the chloronaphthalene (CN) with appropriate concentration affords an E b of 0.14 eV, and thus supporting the excellent efficiency of 16.14%. Meanwhile, the influences of the internal spacing of electron and hole in CT state on device performance were explored for further elucidating carrier micro-transport mechanism and instructing further experimental investigation. [ABSTRACT FROM AUTHOR]

Applying materials with complementary optical absorption spectra to construct tandem solar cell can fulfill further improvement of photovoltaic performance, since tandem solar cell can harvest more photons and enhance the open-circuit voltage of the devices. For tandem solar cells, an interconnecting layer (ICL), which physically and electrically connects the front and the rear subcells, is essential to minimize the energy losses. Herein, we adopt MoO 3 /Ag/PFN-Br as interconnecting layer to join front subcell of PBDTBDD:PC 70 BM and rear subcell of PTB7-Th:IEICO-4F for construction the inverted tandem solar cell with structure of ITO/TIPD/PBDTBDD:PC 70 BM/MoO 3 /Ag/PFN-Br/PTB7-Th:IEICO-4F/MoO 3 /Al. The tandem devices demonstrate strong and wide light response in the wavelength between 300 and 1000 nm. A promising power conversion efficiency (PCE) of 9.74% has been achieved with an open circuit voltage ( V oc ) of 1.503 V. The PCE of tandem cell is 41.36% higher than that (6.89%) of front subcell and 27.82% higher than that (7.62%) of rear subcell. [ABSTRACT FROM AUTHOR]

Tail state Urbach energy caused by the molecular disorder and stacking plays a crucial role for obtaining efficient organic solar cells (OSCs). Herein, we proposed a theoretical and experimental method to adjust the Urbach energy (E U) of organic photoactive materials. Simulation results show that the E U of 32 meV for PM6:Y6-based single junction (SJ) OSCs can enhance J sc and FF significantly, and thus achieving a high photovoltaic conversion efficiency (PCE) of 18.03%. Interestingly, further decreasing E U within a certain range cannot increase device efficiency obviously, and E U cannot be close to 0 meV in consideration of the molecule disorder of organic material. Under the guidance of theoretical design, the ternary component IEICO-4F was introduced to optimize E U Experimental results show that the optimized E U is obtained upon introducing of IEICO-4F, and a championed PCE of 16.61% is achieved when E U is about 25.80 meV for SJ-OSCs. Tandem solar cells (TSCs) reach an experimental PCE of 18.57% when E U is about 27.46 meV, which facilitates current matching between the front and rear sub-cells. [Display omitted] • Suitable E U can realize trade-off among photovoltaic parameters of J sc , FF and V oc. • PM6:Y6-based SJ-OSCs with an E U of 32 meV affords a theoretical PCE of 18.03%. • A ternary component of IEICO-4F is introduced into SJ-OSCs and TSCs to adjust E U. • IEICO-4F is favorable for realizing the current matching between sub-cells in TSCs. • TSCs achieve an experimental PCE of 18.57% after optimization of E U to 27.46 meV. [ABSTRACT FROM AUTHOR]

One of the promising applications for semi-transparent organic solar cells (ST-OSCs) is using as photovoltaic glass windows due to their suitable transparency, comfortable and adjustable color. However, it is difficult to achieve good eye comfort ST-OSCs with suitable average visible transmittance (AVT), power conversion efficiency (PCE) and color rendering index (CRI) because the three factors affect and restrict mutually. To realize ST-OSCs with high performance, theoretical transmittance spectra of ST-OSCs are obtained using the finite-difference time-domain (FDTD) simulation, and then the theoretical optimized structural parameters with appropriate AVT and CRI are achieved. The experimental ST-OSCs output is analyzed under the guidance of theory, and PM6:Y6-based ST-OSCs with Ga 2 O 3 or In 2 O 3 electron collection layers (ECLs) demonstrate outstanding power-generating and chromatic parameters. The PCE for devices with Ga 2 O 3 ECL gets up to 12.6% with an AVT of 22.5% and a CRI of 86.94, and the PCE for devices with In 2 O 3 ECL reaches up to 12.7% with an AVT of 21.5% and a CRI of 88.29. Apparently, the two deep-blue devices guarantee comfortable visual sensations when seeing through the devices, and this work offers a simple approach to achieve power-generating glass with good eye comfort color in energy-saving skyscrapers. [Display omitted] • Good eye comfort ST-OSCs were optimized using finite-difference time-domain. • Ga 2 O 3 and In 2 O 3 were utilized as ECLs for good eye comfort OSCs, respectively. • Ga 2 O 3 -based devices show a PCE of 12.6% with an AVT of 22.5% and a CRI of 86.9. • In 2 O 3 -based devices show a PCE of 12.7% with an AVT of 21.4% and a CRI of 88.3. [ABSTRACT FROM AUTHOR]

In planar heterojunction (PHJ) perovskite solar cells (PerSCs) without mesoporous metal oxide skeleton, there is challenge of formation perovskite film with full coverage to the conductive substrate through solution-process the lead halide precursors. Selecting a lead source with more volatile byproducts is an effective approach to obtain much smoother films with smaller and fewer pinholes. Herein, we demonstrate efficient CH 3 NH 3 PbI 3 /PCBM PHJ PerSCs by using lead acetate (Pb(Ac) 2 ) as lead precursor. The morphology of the perovskite thin films were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively, and the crystalline quality of the perovskite films were investigated by X-ray diffraction (XRD) spectroscopy. Time-resolved photoluminescence (TRPL) was used to investigate the PL lifetime of the perovskite film. The perovskite film derived from Pb(Ac) 2 shows enhanced surface coverage and improved photoluminescence lifetime in comparison with PbI 2 sourced perovskite film. Averaged over 20 individual devices, the power conversion efficiency (PCE) of devices derived from Pb(Ac) 2 reaches 14.81%, much higher than PbI 2 sourced devices by one-step (8.23%) or two-step (10.58%) spin-coating. [ABSTRACT FROM AUTHOR]

The morphology of the photoactive layer critically affects the performance of the bulk heterojunction polymer solar cells (PSCs). To control the morphology, we introduced a hydrophobic fluoropolymer polyvinylidene fluoride (PVDF) as nonvolatile additive into the P3HT:PCBM active layer. The effect of PVDF on the surface and the bulk morphology were investigated by atomic force microscope and transmission electron microscopy, respectively. Through the repulsive interactions between the hydrophilic PCBM and the hydrophobic PVDF, much more uniform phase separation with good P3HT crystallinity is formed within the active layer, resulting enhanced light harvesting and improved photovoltaic performance in conventional devices. The PCE of the conventional device can improve from 2.40% to 3.07% with PVDF additive. The PVDF distribution within the active layer was investigated by secondary ion mass spectroscopy, confirming a bottom distribution of PVDF. Therefore, inverted device structure was designed, and the PCE can improve from 2.81% to 3.45% with PVDF additive. Our findings suggest that PVDF is a promising nonvolatile processing additive for high performance polymer solar cells. [ABSTRACT FROM AUTHOR]

Elucidating charge transportation mechanism for low-temperature solution-processed charge collection layer is crucial for efficient and stable organic solar cells (OSCs). Herein, we present a facile method to fabricate Al(acac) 3 film and integrate it as electron collection layer (ECL) in OSCs. The PM6:Y6-based OSCs with Al(acac) 3 ECL achieve a higher efficiency of 16.12% as compared to the control devices with a 10.90% efficiency. Importantly, the Al(acac) 3 -based devices present superior operational stability, which retains 60% of the initial PCE after 100 h continuous illumination in air. Investigations on optics and carrier recombination dynamics reveal that the improved performance benefits from high up to 98% transparency of Al(acac) 3 ECL, optimized interfacial contact and enhanced exciton dissociation ratio from 85.10% to 97.51%. Further studies on quantified interface resistances during the internal charge transfer indirectly reflect the enhancement of stability. These results highlight the promising prospect of Al(acac) 3 ECL in processing compatible, operationally stable high efficiency OSCs. [Display omitted] • Low-temperature in-situ synthesis is proposed to fabricate Al(acac) 3 film. • Al(acac) 3 is used as electron collection layer in organic solar cells (OSCs). • PM6:Y6-based OSC with an efficiency of 16.12% and good stability are obtained. • Effects of Al(acac) 3 on the internal charge transport have been elucidated. [ABSTRACT FROM AUTHOR]