In recent years, perovskite solar cells have drawn a widespread attention. As an electrode material, fluorine-doped tin oxide (FTO) is widely used in various kinds of solar cells. However, the relatively low work function (WF) (∼4.6 eV) limits its application. The potential barrier between the transparent conductive oxide electrode and the hole transport layer (HTL) in inverted perovskite solar cells results in a decrease in device performance. In this paper, we propose a method to adjust WF of FTO by implanting zirconium ions into the FTO surface. The WF of FTO can be precisely and continuously tuned between 4.59 and 5.55 eV through different dopant concentration of zirconium. In the meantime, the modified FTO, which had a WF of 5.1 eV to match well the highest occupied molecular orbital energy level of poly(3,4-ethylenedioxylenethiophene):polystyrene sulfonate, was used as the HTL in inverted planar perovskite solar cells. Compared with the pristine FTO electrode-based device, the open circuit voltage increased from 0.82 to 0.91 V, and the power conversion efficiency increased from 11.6 to 14.0%.Keywords: FTO; ion implantation; perovskite; solar cell; work function;

•An ammonia-modified PEDOT:PSS HTLs in inverted PSCs was proposed and demonstrated.•The ion-exchange reaction between PSS-H and CH3NH3I was inhibited by simply doping PEDOT:PSS solution with ammonia.•The enhancement of Voc and PCE for the PSCs using the ammonia-doped PEDOT:PSS HTL was observed.Poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS) is one of the most widely used hole transport layers (HTL) in inverted perovskite solar cells (PSCs) due to its simple solution-processed ability, high transparency, and conductivity. However, PEDOT:PSS-based devices suffer a lower open-circuit voltage (Voc) than devices with the conventional structure. To address this issue, we fabricated ammonia-modified PEDOT:PSS films by simply doping PEDOT:PSS solution with different ratio of ammonia. The acidity of PEDOT:PSS can be neutralized by the doped ammonia, which inhibits the ion-exchange reaction between PSS-H and CH3NH3I, thus retarding the reduction of the work function for PEDOT:PSS to some extent. As a result, a superior power conversion efficiency (PCE) of 15.5% was obtained for the device based on the ammonia-doped PEDOT:PSS HTL than that of the pristine PEDOT:PSS-based device. We ascribe the PCE enhancement to the increased Voc and fill factor (FF), which is attributed not only to the better energy-level alignment between the ammonia-modified PEDOT:PSS film and perovskite layer but also to the increased grain size and crystallinity of perovskite film.Download high-res image (175KB)Download full-size image

•TiO2/SnOxCly double layer was firstly employed as the electron transport layer (ETL) for planar perovskite solar cells.•TiO2/SnOxCly based devices exhibit reduced hysteresis and remarkable improvement in device efficiency.•TiO2/SnOxCly ETL could enhance electron extraction and reduce surface trap-state.Recently, perovskite solar cells have attracted tremendous research interest due to their amazing light to electric power conversion efficiency (PCE). However, most high performance devices usually use mesoporous TiO2 as the electron transport layer (ETL), which increases cost for practical application. Here, TiO2/SnOxCly double layer was employed as the ETL for planar perovskite solar cells. Compared with bare TiO2, perovskite solar cell based on TiO2/SnOxCly shows drastically improved power conversion efficiency and reduced hysteresis. These improvements are attributed to TiO2/SnOxCly which could enhance electron extraction and reduce surface trap-state.TiO2/SnOxCly double layer was employed as the electron transport layer for planar perovskite solar cell. Compared with bare TiO2, perovskite solar cell based on TiO2/SnOxCly shows drastically improved power conversion efficiency and reduced hysteresis. These improvements are attributed to TiO2/SnOxCly which could enhance electron extraction and reduce surface trap-state.Download high-res image (253KB)Download full-size image

Organic–inorganic hybrid perovskite solar cells have been developing rapidly in the past several years, and their power conversion efficiency has reached over 20%, nearing that of polycrystalline silicon solar cells. Because the diffusion length of the hole in perovskites is longer than that of the electron, the performance of the device can be improved by using an electron transporting layer, e.g., TiO2, ZnO and TiO2/Al2O3. Nano-structured electron transporting materials facilitate not only electron collection but also morphology control of the perovskites. The properties, morphology and preparation methods of perovskites are reviewed in the present article. A comprehensive understanding of the relationship between the structure and property will benefit the precise control of the electron transporting process and thus further improve the performance of perovskite solar cells.

Ferroelectric materials exhibiting anomalous photovoltaic properties are one of the foci of photovoltaic research. We review the foundations and recent progress in ferroelectric materials for photovoltaic applications, including the physics of ferroelectricity, nature of ferroelectric thin films, characteristics and underlying mechanism of the ferroelectric photovoltaic effect, solar cells based on ferroelectric materials, and other related topics. These findings have important implications for improving the efficiency of photovoltaic cells.具有反常光伏效应的铁电材料是光伏研究的重点之一. 本文综述了铁电材料在光伏应用中的研究进展, 包括铁电性的物理基础、铁电薄膜的性质、铁电光伏效应的特点和内在机制、铁电材料太阳电池等. 这些发现对于进一步提高光伏电池的效率具有重要意义.

A chrysene derivative, BPCC (6,12-bis(9-phenyl-9H-carbazol-3-yl)chrysene), possessing high thermal stability with a high glass transition temperature (Tg = 181 °C) was synthesized. Carbazole groups were introduced to improve its hole transporting properties and suppress crystallization. The device using BPCC as the emitter shows pure saturated blue emission color with coordinates of (0.16, 0.08). Furthermore, utilizing transporting materials with high triplet energy, e.g., TAPC (1,1-bis[4-[N,N-di(p-tolyl)aminophenyl]cyclohexane) and TemPPB (1,2,4,5-tetra(3-pyrid-3-yl-phenyl)benzene) as the hole transport layer (HTL) and electron transport layer (ETL), respectively, the maximum external quantum efficiency (EQE) is 4.9%. It shows a great potential as a highly efficient pure blue emitter for organic light-emitting devices (OLEDs).

A nonadditive hole-transporting material (HTM) of a triphenylamine derivative of N,N′-di(3-methylphenyl)-N,N′-diphenyl-4,4′-diaminobiphenyl (TPD) is used for the organic–inorganic hybrid perovskite solar cells. The power conversion efficiency (PCE) can be significantly enhanced by inserting a thin layer of 1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile (HAT-CN) without adding an ion additive because the hole-transporting properties improve. The short-circuit current density (Jsc) increases from 8.5 to 13.1 mA/cm2, the open-circuit voltage (Voc) increases from 0.84 to 0.92 V, and the fill-factor (FF) increases from 0.45 to 0.59, which corresponds to the increase in PCE from 3.2% to 7.1%. Moreover, the PCE decreases by only 10% after approximately 1000 h without encapsulation, which suggests an alternative method to improve the stability of perovskite solar cells.Keywords: HAT-CN; hole-transport; interfacial; perovskite solar cell; stability

A highly-efficient inverted heterojunction perovskite solar cell was prepared. A homogeneous and compact perovskite (CH3NH3PbI3) layer was prepared via a two-step solution deposition method, and subsequently a double-layer PCBM film was deposited by a sequential spin-coating/vapor deposition process as the electron transport layer. The optimised device could achieve a 12.2% (average 11.09%) efficiency.

In the past two years, the power conversion efficiency (PCE) of organic–inorganic hybrid perovskite solar cells has significantly increased up to 20.1%. These state-of-the-art new devices surpass other third-generation solar cells to become the most promising rival to the silicon-based solar cells. Since the morphology of the perovskite film is one of the most crucial factors to affect the performance of the device, many approaches have been developed for its improvement. This review provides a systematical summary of the methods for morphology control. Introductions and discussions on the mechanisms and relevant hotspots are also given. Understanding the growth process of perovskite crystallites has great benefits for further efficiency improvement and enlightens us to exploit new technologies for large-scale, low-cost and high-performance perovskite solar cells.

•A new fullerene derivative PCBAb is used as the acceptor in polymer solar cells.•The electron mobility of PCBAb responds notably to UV and VIS light.•The devices are switched between “active” and “sleep” by UV and VIS treatments.•The PCEs of “active” and “sleep” devices are 2.0% and 0.4% respectively.[6,6]-Phenyl-C61-butyric acid-4′-hydroxyl-azobenzene ester (PCBAb) was synthesized and used as the acceptor in the fabrication of reversible UV–VIS response bi-state polymer solar cells (PSCs) based on the photoinduced cis–trans isomerization of PCBAb. The device can be switched between “active” and “sleep” by the irradiation of UV and visible light, respectively. The active device has a PCE of 2.0%. With UV irradiation, the device goes to “sleep” with a lowered PCE (0.4%), and simultaneously decreased Jsc, Voc and FF, while after visible light treatment, the device is made “active” again. The mechanism of the bi-state process involves the different electron mobilities of the isomers.

•Polarizing PSCs are fabricated by liquid crystalline self-organization technique.•PEDOT:PSS alignment layer induces upper PBTTT molecules to orient uniaxially.•The dichroic ratio of oriented PBTTT film is ca. 6.35 at absorption peak.•Polarizing PSCs have more competitive PCE compare to isotropic PSCs.•Parallel excitation produces longer exciton lifetime in uniaxial aggregation.We manufactured polarizing polymer solar cells (PSCs) utilizing a liquid crystalline polymer (i.e., poly(2,5-bis(3-dodecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT)) as an electron donor material and a material that selectively absorbs polarized light. The oriented PBTTT films prepared using a self-organization process exhibited a high dichroic ratio of ca. 6.35 at the absorption peak. The polarizing PSCs based on oriented PBTTT–PC71BM photoactive layers exhibit an anisotropic photovoltaic effect under polarized illumination along the two orthogonal axes. The polarizing PSCs have a larger power conversion efficiency under parallel-polarized illumination than that of isotropic PV devices under unpolarized illumination. Based on picosecond fluorescent spectra, the parallel excitation produces a slower ground state recovery and a longer exciton lifetime than perpendicular excitation for PBTTT molecules in a uniaxially oriented arrangement.

Recently, highly efficient solar cells based on organic–inorganic perovskites have been intensively reported for developing fabricating methods and device structures. Additional power conversion efficiency should be gained without increasing the thickness and the complexity of the devices to accord with practical applications. In this paper, a rough interface between perovskite and HTM was fabricated in perovskite solar cells to enhance the light scattering effect and improve the charge transport. The parameters related to the morphology have been systematically investigated by sequential deposition. Simultaneous enhancements of short-circuit current and power conversion efficiency were observed in both CH3NH3PbI3 and CH3NH3PbI3−xClx devices containing the rough interface, with power conversion efficiencies of 10.2% and 10.8%, respectively. Our finding provides an efficient and universal way to control the morphology and further optimize perovskite solar cells for devices by sequential deposition with various structures.

An oligothiophene derivative named DR3TBDTT with high hydrophobicity was synthesized and functioned as the hole transporting material without an ion additive. 8.8% of power conversion efficiency was obtained for CH3NH3PbI3−xClx based planar solar cells with improved stability, compared to devices using Li-TFSI doped spiro-MeOTAD.

A spirobifluorene derivative containing phenanthrene moiety, 2,7-di(phenanthren-9-yl)-9,9′-spirobifluorene (DPSF), has been synthesized. It shows absorption peaks at 254 nm, 310 nm, and 327 nm and a fluorescence peak at 383 nm in CHCl3 that shifts to 398 nm in the film state. The quantum yield is 0.79 calibrated with a standard of coumarin 102 (0.93). A pure blue emission at Commission Internationale de l′Éclairage (CIE) (0.15, 0.08), has been achieved using DPSF as the emitter, poly(3,4-ethylene dioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS) as the hole injecting layer, 4,4′-bis[N-(1-naphthyl)-N-phenyl-amino] biphenyl (NPB) as the hole transporting layer, and 1,3,5-tris(N-phenylbenzimidazol-2-yl)-benzene (TPBI) mixing with 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PBD) (2:1) as the electron transporting material. The maximum current efficiency (CE) and power efficiency (PE) of the DPSF device are 3.24 cd A−1 and 2.54 lm W−1, corresponding to 5.41% of maximum external quantum efficiency (EQE). The spirobifluorene derivative show high thermal stabilities, 178 °C for the glass transition temperature (Tg) and 503 °C for the decomposition temperature (Td). The synthesized spirobifluorene derivative shows potential application as a highly efficient pure blue emitter for organic light emitting devices (OLED).

Highly efficient deep-blue organic light-emitting devices (OLEDs) have been fabricated using 2,7-di(2,2′:6′,2″-terpyridin-4-yl)-9,9-dioctyl-9H-fluorene (DTPF) as the emitter, which has a wide energy gap, high emission quantum yield (Φf = 0.88), and high electron transporting property to improve the charge balance. A high efficiency of 2.55 cd/A and 2.67 lm/W are obtained in OLED. The device also exhibits a low turn-on voltage of 3.0 V and Commission Internationale de l′Éclairage (CIE) coordinates of (0.16, 0.09).Keywords: charge balance; deep-blue; electron transport; emitter; organic light-emitting device;

A high triplet energy (ET = 3.2 eV) electron transporting/hole blocking (ET/HB) material, 1,2,4,5-tetra(3-pyrid-3-yl-phenyl)benzene (TemPPB) with a super twisted structure and high thermal stability has been synthesized. An external quantum efficiency (EQE) of 19.6% was achieved by using TemPPB as the ET/HB material in a blue electrophosphorescent device, much higher than the EQE of 12.5% for the device using the conventional ET material, 3-(4-biphenyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (TAZ). In addition, the weak ET property of TemPPB resulting from its super twisted structure can be enhanced via n-type doping with LiF. An EQE of 24.5% was achieved by combining n-type doping and a double-emission layer. This shows an alternative way to design ET/HB materials with high ET and improved thermal stability for blue electrophosphorescent devices.

An oligothiophene derivative named DR3TBDTT with high hydrophobicity was synthesized and functioned as the hole transporting material without an ion additive. 8.8% of power conversion efficiency was obtained for CH3NH3PbI3−xClx based planar solar cells with improved stability, compared to devices using Li-TFSI doped spiro-MeOTAD.

A highly-efficient inverted heterojunction perovskite solar cell was prepared. A homogeneous and compact perovskite (CH3NH3PbI3) layer was prepared via a two-step solution deposition method, and subsequently a double-layer PCBM film was deposited by a sequential spin-coating/vapor deposition process as the electron transport layer. The optimised device could achieve a 12.2% (average 11.09%) efficiency.

A chrysene derivative, BPCC (6,12-bis(9-phenyl-9H-carbazol-3-yl)chrysene), possessing high thermal stability with a high glass transition temperature (Tg = 181 °C) was synthesized. Carbazole groups were introduced to improve its hole transporting properties and suppress crystallization. The device using BPCC as the emitter shows pure saturated blue emission color with coordinates of (0.16, 0.08). Furthermore, utilizing transporting materials with high triplet energy, e.g., TAPC (1,1-bis[4-[N,N-di(p-tolyl)aminophenyl]cyclohexane) and TemPPB (1,2,4,5-tetra(3-pyrid-3-yl-phenyl)benzene) as the hole transport layer (HTL) and electron transport layer (ETL), respectively, the maximum external quantum efficiency (EQE) is 4.9%. It shows a great potential as a highly efficient pure blue emitter for organic light-emitting devices (OLEDs).

A spirobifluorene derivative containing phenanthrene moiety, 2,7-di(phenanthren-9-yl)-9,9′-spirobifluorene (DPSF), has been synthesized. It shows absorption peaks at 254 nm, 310 nm, and 327 nm and a fluorescence peak at 383 nm in CHCl3 that shifts to 398 nm in the film state. The quantum yield is 0.79 calibrated with a standard of coumarin 102 (0.93). A pure blue emission at Commission Internationale de l′Éclairage (CIE) (0.15, 0.08), has been achieved using DPSF as the emitter, poly(3,4-ethylene dioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS) as the hole injecting layer, 4,4′-bis[N-(1-naphthyl)-N-phenyl-amino] biphenyl (NPB) as the hole transporting layer, and 1,3,5-tris(N-phenylbenzimidazol-2-yl)-benzene (TPBI) mixing with 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PBD) (2:1) as the electron transporting material. The maximum current efficiency (CE) and power efficiency (PE) of the DPSF device are 3.24 cd A−1 and 2.54 lm W−1, corresponding to 5.41% of maximum external quantum efficiency (EQE). The spirobifluorene derivative show high thermal stabilities, 178 °C for the glass transition temperature (Tg) and 503 °C for the decomposition temperature (Td). The synthesized spirobifluorene derivative shows potential application as a highly efficient pure blue emitter for organic light emitting devices (OLED).

A high triplet energy (ET = 3.2 eV) electron transporting/hole blocking (ET/HB) material, 1,2,4,5-tetra(3-pyrid-3-yl-phenyl)benzene (TemPPB) with a super twisted structure and high thermal stability has been synthesized. An external quantum efficiency (EQE) of 19.6% was achieved by using TemPPB as the ET/HB material in a blue electrophosphorescent device, much higher than the EQE of 12.5% for the device using the conventional ET material, 3-(4-biphenyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (TAZ). In addition, the weak ET property of TemPPB resulting from its super twisted structure can be enhanced via n-type doping with LiF. An EQE of 24.5% was achieved by combining n-type doping and a double-emission layer. This shows an alternative way to design ET/HB materials with high ET and improved thermal stability for blue electrophosphorescent devices.

In the past two years, the power conversion efficiency (PCE) of organic–inorganic hybrid perovskite solar cells has significantly increased up to 20.1%. These state-of-the-art new devices surpass other third-generation solar cells to become the most promising rival to the silicon-based solar cells. Since the morphology of the perovskite film is one of the most crucial factors to affect the performance of the device, many approaches have been developed for its improvement. This review provides a systematical summary of the methods for morphology control. Introductions and discussions on the mechanisms and relevant hotspots are also given. Understanding the growth process of perovskite crystallites has great benefits for further efficiency improvement and enlightens us to exploit new technologies for large-scale, low-cost and high-performance perovskite solar cells.