All-inorganic CsPbBr3 Perovskite Solar Cells Research Articles

Energy Level Tuning in CsPbBr3 Perovskite Solar Cells through In Situ-Polymerized PEDOT Hole Transport Layer.

The all-inorganic CsPbBr3 perovskite solar cells exhibit excellent stability against humidity and thermal conditions as well as relatively low production cost, rendering them a gradually emerging research hot spot in the field of photovoltaics. However, the absence of a hole transport layer (HTL) in its common structure and the substantial energy level difference of up to 0.6 eV between the highest occupied molecular orbital (HOMO) level of CsPbBr3 and the work function of the carbon electrode have emerged as the primary factor limiting the improvement of its power conversion efficiency (PCE). In this work, the monomer 2,5-dibromo-3,4-ethylenedioxythiophene (DBEDOT) is spin-coated onto the surface of the CsPbBr3 film directly and then subjected to annealing; DBEDOT undergoes in situ polymerization to form poly(3,4-ethylenedioxythiophene) (PEDOT), which aims to ameliorate the issue of excessive energy level difference between CsPbBr3 and the carbon electrode, and to facilitate the extraction and transport efficiency of holes between the CsPbBr3 perovskite and the carbon electrode. Compared to the pristine device, the PCE of the device based on in situ polymerization is enhanced and achieves a maximum efficiency of 9.81%. Furthermore, the unencapsulated devices based on in situ polymerization maintain 95.9% of their original efficiency after 40 days of stability testing.

Preparation of Highly Efficient and Stable All-Inorganic CsPbBr3 Perovskite Solar Cells Using Pre-Crystallization Multi-Step Spin-Coating Method

All-inorganic CsPbBr3 perovskite solar cells have garnered extensive attention in the photovoltaic domain due to their remarkable environmental stability. Nevertheless, CsPbBr3 prepared using the conventional sequential deposition method suffers from issues such as inferior crystallinity, low phase purity, and poor film morphology. Herein, we propose a pre-crystallization methodology by introducing a minute quantity of CsBr into the PbBr2 precursor solution to generate a small amount of CsPb2Br5 crystals within the PbBr2 film, leading to a porous PbBr2 film with enhanced crystallinity. Under the influence of more pores and CsPb2Br5 crystals as nucleation sites for inducing growth, a CsPbBr3 film with a larger crystal size, lower grain boundary density, stronger crystallinity, and higher phase purity is formed. Compared with untreated devices, photovoltaic devices prepared using the pre-crystallization method achieved a champion photovoltaic conversion efficiency (PCE) of 8.62%. Furthermore, pre-crystallized devices demonstrate higher stability than untreated ones and can still retain 94% of the original PCE after being exposed to air for 1000 h without encapsulating.

Reducing oxygen vacancies of MoO3 by polyaniline functionalization for stable and efficient inorganic tri-brominated perovskite solar cells

The photovoltaic performance of perovskite solar cells (PSCs) is closely dependent on the efficient carrier extraction and transport at the interface. Here, a polyaniline (PANI) functionalized MoO3 (PANI/MoO3) hole transport material (HTM) is exploited to perfect the interface between the perovskite layer and carbon electrode in all-inorganic CsPbBr3 PSCs. After functionalization with PANI, the p-type behavior and the hole mobility and conductivity of MoO3 are improved by reducing the oxygen vacancies, which boosts the hole extraction and transport, energy level arrangement at the interface of CsPbBr3 perovskite/(PANI/MoO3) HTM. Meanwhile, the PANI/MoO3 with rich C–N and N–H groups introduced by PANI passivates the ions trap states of perovskite films by the C–N⋯Pb2+ (Cs+) Lewis acid-base coordination and the N–H⋯Br− hydrogen bonding, leading to an effective suppression of non-radiative recombination for improved carrier extraction. As a result, the PANI/MoO3 HTMs-based CsPbBr3 PSCs obtain a remarkably increased power conversion efficiency of 10.41 %, in comparison with the efficiency of the original device (6.55 %). In addition, the unencapsulated device with PANI/MoO3 HTMs shows excellent long-term stability with 93.9 % maintenance of the initial efficiency after storing in air with 85 % relative humidity and at 85 °C for 30 days.

Enhancing carrier collection in CsPbBr3 solar cells through crystal orientation and defect passivation

All-inorganic carbon-based CsPbBr3 perovskite solar cells (PSCs) have gained growing interest for their remarkable stability. However, compared to their organic–inorganic hybrid counterparts, there is still substantial room for improving their performance primarily due to the inferior photogenerated carrier collection efficiency. Here, we employ area-dependent transient photocurrent to assess the carrier transit time in CsPbBr3 PSCs, revealing that an extended carrier transit time relative to the lifetime significantly contributes to their low carrier collection efficiency. To address this challenge, we narrow the gap between carrier transit time and lifetime by introducing a dual-functional additive, serving to facilitate both crystallization orientation and defect passivation. Consequently, we achieve enhanced short-circuit current and efficiency in CsPbBr3 PSCs.

Boosting the efficiency and stability of CsPbBr3 perovskite solar cells through modified multi-step spin-coating method

In this research, we enhance the stability of all-inorganic CsPbBr3 perovskite solar cells using a modified multi-step spin-coating technique. By introducing low-concentration CsBr and PbBr2 in two additional steps, we achieve a PbBr2 layer with fewer pinholes, improved crystallinity, and a smoother surface. This promotes the formation of a high-quality CsPbBr3 film with larger grains by incorporating a derivative-phase CsPb2Br5. This film reduces interface defects, enhances grain growth, and boosts power conversion efficiency from 5.43% to 9.36%. Notably, unencapsulated devices maintain stable performance for over 2400 h in ambient air conditions.

Highly stable all-inorganic CsPbBr3 perovskite solar cells based on pulsed laser deposition

In the highly efficient n-i-p structure of perovskite solar cells (PSCs), organic material Spiro-OMeTAD is usually used as the hole transport layer (HTL). However, its high hygroscopicity and thermal instability seriously limit its commercial application. In contrast, nickel oxide (NiOx) is a promising alternative due to its wideband gap, low cost, and high stability. By comparing with traditional spin coating, pulsed laser deposition (PLD) can produce relatively compact films and avoid the damage of solvent evaporation on the morphology and crystal quality, thus improving the device stability. This work introduces PLD to prepare CsPbBr3 and NiOx thin films to obtain highly stable all-inorganic CsPbBr3-based PSCs. Carrier dynamics are studied via electrochemical measurements and transient absorption spectroscopy. The power conversion efficiency of the all-inorganic CsPbBr3-based PSCs with NiOx HTL can be improved to 5.47% under optimum thickness and annealing temperature. It is revealed that the thermal stability is significantly enhanced, where unencapsulated all-inorganic CsPbBr3 PSCs specifically can maintain 95% of initial efficiency for 1200 h under the condition of 85 °C and 30% relative humidity.

Ultrahigh fill-factor all-inorganic CsPbBr3 perovskite solar cells processed from two-step solution method and solvent additive strategy

All-inorganic CsPbBr3 perovskite solar cells (PSCs) have attracted more attentions due to the excellent environmental stability, however, the wide bandgap and relatively poor crystallinity of CsPbBr3 have been the main obstacle to improve their power conversion efficiency (PCE). Herein, we proposed an efficient and simple strategy of precursor additive in the two-step aqueous-solution method, the resulted CsPbBr3 film has achieved more uniform grain size, almost pure perovskite phase, smoother surface, less defects, enhanced light absorption and longer carrier lifetime. This is due to the rapid evaporation of additive (IPA and CH3OH) in the CsBr/H2O precursor leads to a relatively higher local CsBr concentration on the surface of PbBr2, which can provide more nucleation sites and accelerate the crystallization of perovskite. Further, when utilizing the optimal additive of 5% (in volume) IPA, the HTM-free carbon-based CsPbBr3 PSCs obtained a PCE improvement from 9.09% to 10.29%, and an ultrahigh fill factor (FF) of 85.21%. What is more, by adding 0.1 mol/L PbCl2 into the PbBr2 solution in the first step, the open circuit voltage of device has increased from 1.36 V to 1.48 V, the champion PCE reached 10.37% (steady output PCE of 10.17%), and the non-encapsulated device could maintain 85% of its initial efficiency after 50 d in the air. This work provides a cost-effective approach to grow CsPbBr3 film and boosts the efficiency benchmark of the CsPbBr3 PSCs to more than 10%, it is desirable that the highly efficient and stable CsPbBr3 PSCs can be developed in future.

Interfacial modification of in-situ polymerized AMPS/NiFe2O4 quantum dots for efficient and air-stable CsPbBr3 perovskite solar cells

The regulation of the interface energetics and the simultaneous passivation of the surface defects of perovskite (PVK) film play an important role in improving the efficiency and stability of perovskite solar cells (PSCs). Here, a composite modification of poly(2-acrylamide-2-methylpropanesulfonic acid) (PAMPS)/NiFe2O4 quantum dots (NQDs) that is formed by the light-triggered polymerization of AMPS monomer in homogeneous AMPS/NQDs is launched at the interface of PVK/carbon in all-inorganic CsPbBr3 PSCs. Due to the higher hole mobility and conductivity of PAMPS/NQDs and its interface modification induced better energy level alignment and interfacial contact, the hole transport and extraction are significantly promoted. Combined with the simultaneous passivation of cations and anions (Cs+, Pb2+ and Br-) defects on CsPbBr3 PVK surface by the SO, CO, NH and OH groups in PAMPS, the non-radiative recombination is effectively restrained, rendering a champion power conversion efficiency of 10.21 % with excellent high humidity and temperature (85 % RH, 85 °C) and light soaking tolerances for PAMPS/NQDs composite modified carbon-based CsPbBr3 PSCs without encapsulation in air, which is markedly higher than the 6.81 % efficiency of the control device.

Charge transfer doping of graphene oxide with nickel oxide nanoparticles for stable and efficient carbon-based, all-inorganic CsPbBr3 perovskite solar cells.

All-inorganic CsPbBr3 perovskite solar cells have received growing attention in the photovoltaic field due to their high stability, low cost, and simple preparation processes. However, the high-density defects in perovskite films and the large energy differences at interfaces have been the main challenges for achieving high power conversion efficiency and good stability. In this work, nickel oxide (NiOx) decorated graphene oxide (GO) is used as a hole collector at the perovskite/carbon interface for a carbon-based CsPbBr3 perovskite solar cell. The crystallinity of the CsPbBr3 perovskite layer and the hole extraction ability are markedly enhanced because of the p-type charge transfer doping of GO from oxygenic groups to NiOx. Finally, the all-inorganic CsPbBr3 perovskite solar cell achieves a power conversion efficiency of 8.59%. More importantly, the best solar cell free of encapsulation retains 94.2% of its initial efficiency in an air environment over 21 days.

Synergistic effect of alkali metal doping and thiocyanate passivation in CsPbBr3 for HTM-free all-inorganic perovskite solar cells.

All-inorganic CsPbBr3 perovskite solar cells (PSCs) without hole-transport materials (HTMs) have attracted widespread attention because of their significant environmental stability. However, the poor quality of perovskite film and the energetics mismatch between CsPbBr3 and charge-transport layers limit the further improvement of the CsPbBr3 PSC performance. To solve this issue, the synergistic effect of alkali metal doping and thiocyanate passivation in NaSCN and KSCN dopants is utilized to improve the properties of the CsPbBr3 film. The Na+ and K+ with smaller ionic radii are doped at the A-site of CsPbBr3 to cause a lattice contraction, which contributes to the formation of CsPbBr3 film with enhanced grain size and crystallinity. The SCN- exerts the function of passivating the uncoordinated Pb2+ defects of CsPbBr3 film, leading to a reduction of trap state density. The incorporation of NaSCN and KSCN dopants also adjusts the band structure of CsPbBr3 film to improve the interfacial energetics match of the device. As a result, the charge recombination is suppressed, and the charge transfer and extraction are effectively promoted, delivering a highly enhanced power conversion efficiency of 10.38% for the champion KSCN doped CsPbBr3 PSCs without HTMs compared to 6.72% efficiency for the original device. Moreover, the stability of the unencapsulated PSCs under ambient conditions with high humidity (85% RH, 25 °C) is distinctly improved, retaining 91.1% of the initial efficiency after 30 days of aging.

Stable and highly efficient all-inorganic CsPbBr3 perovskite solar cells by interface engineering with NiO NCs modification

The existence of considerable energy level differences and defects at interfaces between the CsPbBr3 film and the carbon electrode, have been critical bottlenecks to restrict the development of the photoelectric conversion efficiencies (PCEs) of all-inorganic CsPbBr3 perovskite solar cells (PSCs). Therefore, to solve this contradiction, the interface engineering has been applied into the interface of CsPbBr3/carbon through many passivators. However, most of the passivators reported previously are composed of organic ingredients, which is inconsistent with the concept of the “real all-inorganic” PSCs. Here, NiO nanocrystals (NiO NCs) with hole transporting behaviors were prepared by hydrothermal synthesis method and applied to modify the interface between the CsPbBr3 film and carbon electrode. After NiO NCs modified, the CsPbBr3 film with a smoother surface exhibits suppressed interface defects and appropriate interfacial energy band alignment, thereby decreasing the carrier recombination and improving the charge extraction ability. Eventually, by optimizing the concentrations of NiO NCs and the spin-coating cycles of CsBr methanol solution, the NiO NCs-treated device generates a champion efficiency of 9.19% with a short-circuit current (JSC) of 7.57 mA cm−2, an open-circuit voltage (VOC) of 1.57 V and a fill factor (FF) of 77.44%, in comparison with the pristine device with an inferior efficiency of 7.15%, a JSC of 6.92 mA cm−2, a VOC of 1.48 V and an FF of 69.64%. Furthermore, the NiO NCs modified devices show no significant degradation after 30 days in open-air conditions.

Phase Control of Cs-Pb-Br Derivatives to Suppress 0D Cs4 PbBr6 for High-Efficiency and Stable All-Inorganic CsPbBr3 Perovskite Solar Cells.

The precise phase control of Cs-Pb-Br derivatives from 3D CsPbBr3 to 0D Cs4 PbBr6 highly determines the photovoltaic performance of all-inorganic CsPbBr3 perovskite solar cells (PSCs). Herein, the preferred phase conversion from precursor to Cs-Pb-Br derivatives is revealed by theoretically calculating the Gibbs free energies (∆G) of various phase conversion processes, allowing for a simplified multi-step solution-processable spin-coating method to hinder the formation of detrimental 0D Cs4 PbBr6 phase and enhance the photovoltaic performance of a PSC because of its large exciton binding energy, which is regarded as a recombination center. By further accelerating the interfacial charge extraction with a novel 2D transition metal dichalcogenide ReSe2 , the hole-free CsPbBr3 PSC achieves a champion efficiency of 10.67% with an impressive open-circuit voltage of 1.622V and an excellent long-term stability. This work provides an in-depth understanding on the precise Cs-Pb-Br perovskite phase control and the effect of derivatives on photovoltaic performance of advanced CsPbBr3 PSCs.

All-inorganic CsPbBr3 perovskite solar cells with enhanced efficiency by exploiting lone pair electrons via passivation of crystal boundary using carbon nitride (g-C3N4) nanosheets

Fast extraction of photo-generated charge plays a crucial function in improving the photovoltaic conversion efficiency (PCE) of the perovskite solar cells (PSCs). Here, an effective strategy to decrease the charge recombination losses by introducing versatile carbon nitride (g-C3N4) nanosheets to the CsPbBr3 films was demonstrated. The incorporation of the g-C3N4 additive can restrain the nucleation and crystalline growth rate of perovskite films by an interaction of lone pair electrons from the exposed N atoms to the PbBr2 precursor, resulting in high-quality CsPbBr3 films with an increase in crystalline size. Notably, a ‘coupling effect’ between the lone pair electrons from g-C3N4 nanosheets and unsaturated Pb dangling bonds (Br vacancies) around the grain boundaries significantly decreases trap states caused by defects, leading to the fewer recombination centers in CsPbBr3 films. The g-C3N4 nanosheets serving as an energy barrier can also successfully suppress the recombination loss of back electrons with holes from the g-C3N4 interface, yielding a superior PCE of 8.0% with a fill factor of 80.25%. The result opens an alternative path to enhance the performance of CsPbBr3 PSCs by passivating the trap states of perovskite films with the improvement of the crystallization quality and charge extraction efficiency.

Dimensionality Control of SnO2 Films for Hysteresis-Free, All-Inorganic CsPbBr3 Perovskite Solar Cells with Efficiency Exceeding 10.

The all-inorganic cesium lead bromide (CsPbBr3) perovskite solar cells (PSCs) have attracted considerable interest because of their outstanding environmental stability and low manufacturing cost. However, the state-of-the-art mesoscopic titanium dioxide (TiO2) electron-transporting layers (ETLs) always present low electron mobility, are destructive to perovskites under ultraviolet light illumination, as well as possess high sintering temperature. Nanostructured tin dioxide (SnO2) is a promising electron-transporting material for high-efficiency PSCs due to matching energy-level alignment with the perovskite layer, improved optical transparency, high electron mobility, excellent photostability, and low-temperature processing. Furthermore, rapid but poorly controlled perovskite crystallization makes it difficult to scale up planar PSCs for industrial applications. To address this issue, we adopt a dimensional SnO2 ETL to change the surface wettability for uniform perovskite coverage over large areas and the growth of large-sized CsPbBr3 grains, resulting in a maximum grain size of 1.65 μm. Moreover, the dimensional SnO2 ETL could increase the interfacial contact area between the CsPbBr3 layer and the ETL and enhance the electronic contact for efficient electron extraction to suppress or to eliminate the notorious hysteresis behavior. As expected, a power conversion efficiency (PCE) of 9.51% with an almost hysteresis-free phenomenon is achieved through dimensionality control of SnO2 films attributed to the remarkably enhanced light harvesting, accelerated electron extraction, diminished defect density, and reduced charge recombination. Upon further interfacial modification with graphene quantum dots (GQDs), the PSC based on the two-dimensional SnO2 ETL achieves a champion PCE of 10.34% due to the improved energy-level alignment at the device interface. Moreover, the best all-inorganic CsPbBr3 PSC free of encapsulation retains 93% of initial efficiency over 10 days at 80% relative humidity. This work provides an effective dimensionality control strategy for optimized charge transportation and enlarged perovskite grain size to make stable and efficient all-inorganic CsPbBr3 PSCs.

Flexible, All-Inorganic CsPbBr3 Perovskite Solar Cells Tailored by Heat-resistant Muscovite Substrates.

All-inorganic CsPbBr3 perovskite solar cells (PSCs) have attracted tremendous attention, owing to their excellent stability and rising power conversion efficiency. However, the mechanical flexibility of these solar cells has ground to a standstill because of the high-temperature requirement for ideal CsPbBr3 perovskite films. In this study, a flexible CsPbBr3 PSC with an efficiency of 5.71 % has been made by means of fabricating a heat-resistant conductive muscovite substrate, which demonstrates very high mechanical flexibility with nearly unchanged resistance even after 4000 bending cycles (12000 cycles of concave and convex bending for PSCs), owing to the weak van der Waals force and layered structure. Implementation of the muscovite substrate enables the fabrication of flexible PSCs under high-temperature conditions, providing a new path to increase the efficiency without lowering the crystallization temperature of state-of-the-art electron-transporting materials and perovskite films in the future.

Multifunctional brominated graphene oxide boosted charge extraction for high-efficiency and stable all-inorganic CsPbBr3 perovskite solar cells

The perovskite film with large grain size and high charge mobility is critical for the improvement of the power conversion efficiency (PCE) and the operational stability of perovskite solar cells (PSCs). Herein, multifunctional brominated graphene oxide (Br-GO) is prepared and innovatively used as an effective additive to incorporate into CsPbBr3 to form a large-grained high-quality perovskite film and to passivate defects at grain boundaries, which remarkably reduces the trap state density and carrier non-radiative recombination. Meanwhile, the hole mobility of the homogeneous CsPbBr3 + Br-GO photoactive layer is obviously increased due to the hole acceptor properties and high carrier mobility of Br-GO, resulting in an enhanced charge separation as well as transfer and suppressed carrier radiative recombination. Moreover, the Br-GO with a downshift valence band is employed as a hole-transporting material setting at perovskite/Carbon interface to further compensate energy levels and promote hole extraction. As a consequence, a champion PCE of 10.10% with an open-circuit voltage up to 1.602 V for the optimized PSCs with a configuration of FTO/c-TiO2/m-TiO2/CsPbBr3 + Br-GO/Br-GO/Carbon is obtained, which is much higher than 6.28% efficiency for the reference device. The unencapsulated solar cells also exhibit a remarkable tolerance toward 85% RH and long-term AM 1.5G illumination in air.

Enhanced hole extraction by electron-rich alloys in all-inorganic CsPbBr3 perovskite solar cells.

We present the fabrication of electron-rich Pt3M alloy-tailored carbon electrodes to maximize hole extraction. Through optimizing the doses and alloy species systematically, the best all-inorganic CsPbBr3 perovskite solar cell achieved a power conversion efficiency of 9.08% and showed excellent long-term stability at 80% RH over 20 days.

Tailoring organic bulk-heterojunction for charge extraction and spectral absorption in CsPbBr3 perovskite solar cells

All-inorganic CsPbBr3 perovskite solar cells (PSCs) are promising candidates to balance the stability and efficiency issues of organic-inorganic hybrid devices. However, the large energy barrier for charge transfer and narrow spectral response are still two challenging problems for performance improvement. We present here an organic bulk-heterojunction {poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl C61 butyric acid methyl ester (P3HT: PCBM)} photoactive layer to boost the charge extraction and to widen the spectral absorption, achieving an enhanced power conversion efficiency up to 8.94% by optimizing the thickness of P3HT: PCBM photoactive layer, which is much higher than 6.28% for the pristine CsPbBr3 device. The interaction between the carbonyl group in PCBM and unsaturated Pb atom in the perovskite surface can effectively passivate the defects and reduce charge recombination. Furthermore, the coupling effect between PCBM and P3HT widens the spectral response from 540 to 650 nm for an increased short-circuit current density. More importantly, the devices are relatively stable over 75 days upon persistent attack by 70% relative humidity in air condition. These advantages of high efficiency, excellent long-term stability, cost-effectiveness and scalability may promote the commercialization of inorganic PSCs.

Interfacial Strain Release from the WS2 /CsPbBr3 van der Waals Heterostructure for 1.7 V Voltage All-Inorganic Perovskite Solar Cells.

Perovskite lattice distortion induced by residual tensile strain from the thermal expansion mismatch between the electron-transporting layer (ETL) and perovskite film causes a sluggish charge extraction and transfer dynamics in all-inorganic CsPbBr3 perovskite solar cells (PSCs) because of their higher crystallization temperatures and thermal expansion coefficients. Herein, the interfacial strain is released by fabricating a WS2 /CsPbBr3 van der Waals heterostructure owing to their matched crystal lattice structure and the atomically smooth dangling bond-free surface to act as a lubricant between ETL and CsPbBr3 perovskite. Arising from the strain-released interface and condensed perovskite lattice, the best device achieves an efficiency of 10.65 % with an ultrahigh open-circuit voltage of 1.70 V and significantly improved stability under persistent light irradiation and humidity (80 %) attack over 120 days.

Polymer-induced lattice expansion leads to all-inorganic CsPbBr3 perovskite solar cells with reduced trap density

All-inorganic perovskite materials (CsPbBr3) with long-term stability have been attracted enormous attention for commercialization. Here, a one-step spin-coating method was employed to yield high-purity CsPbBr3 perovskite films. The polyethylene glycol (PEG) was introduced into a precursor solution to balance the nucleation and growth rate. Noticeably, adding a polymeric material of PEG also leaded to a uniform lattice expansion in CsPbBr3 thin layers. The polymer-induced lattice expansion benefits the performances of a CsPbBr3 device due to reduced trap density, boosting the power conversion efficiency. This work emphasizes that controlled lattice expansion benefits in enhancing the electronic functionalities of perovskites.