Efficient polymer solar cells employing a non-conjugated small-molecule electrolyte

Abstract

Polymer solar cells have drawn a great deal of attention due to the attractiveness of their use in renewable energy sources that are potentially lightweight and low in cost. Recently, numerous significant research efforts have resulted in polymer solar cells with power conversion efficiencies in excess of 9% (ref. 1). Nevertheless, further improvements in performance are sought for commercial applications. Here, we report polymer solar cells with a power conversion efficiency of 10.02% that employ a non-conjugated small-molecule electrolyte as an interlayer. The material offers good contact for photogenerated charge carrier collection and allows optimum photon harvesting in the device. Furthermore, the enhanced performance is attributed to improved electron mobility, enhanced active-layer absorption and properly active-layer microstructures with optimal horizontal phase separation and vertical phase gradation. Our discovery opens a new avenue for single-junction devices by fully exploiting the potential of various material systems with efficiency over 10%.In recent decades, polymer solar cells (PSCs) based on conjugated polymers as donors (D) blended with fullerene derivatives as acceptors (A) have received an enormous amount of attention in renewable energy sources because of the promise of low cost, flexibility and large-area fabrication 2-5 . To date, the best reported power conversion efficiency (PCE) in PSCs is ∼9-10%, but most values remain below 10%, especially in single-junction PSCs 6-11 . It is therefore highly desirable to develop novel materials and devices for the creation of single-junction PSCs with excellent efficiencies.To achieve such high efficiencies, energy loss in PSCs should be minimized. In general, energy loss originates directly from the reflection, transmission, exciton recombination and exciton annihilation of active and/or interface layers, as well as the accumulation on electrodes. The key is therefore to develop suitable materials for active and interfacial layers that can significantly reduce the loss of energy. For active-layer materials, considerable progress has been demonstrated with broadband absorption and high carrier mobility, resulting in state-of-the-art single-junction PSCs with PCEs up to ∼10% 12,13 . Meanwhile, triple-junction tandem devices have also been developed that achieve a high PCE of 11.5%, by combining different high-performance active-layer materials [14][15][16] . Before the studies on active-layer materials and devices, the interlayer between the cathode and active layer was also thought to be an important factor in the realization of highly efficient PSCs by avoiding the accumulation of excitons. The selection of proper electrodes with matched workfunctions is an effective method to reduce this accumulation and improve efficiency. However, the availability of suitable electrodes is limited for the emerging active-layer materials of different energy levels, so some investigators have suggested using an interfacial layer between the active layer and electro...

Insights into the working mechanism of cathode interlayers in polymer solar cells via [(C8H17)4N]4[SiW12O40]

“…The certied PCE result is 4.4% lower than the average value (9.93%) in our lab mainly due to the decrease of FF, which can be attributed to non-ideal cell encapsulation. 6,28 In addition, we also examined its function as a CIL in the PSCs based on PCDTBT:PC 71 BM. As shown in Fig.…”

“…1a) up to 10% though its working mechanism is unclear. 28 Thereby non-conjugated molecules should be regarded as the potentially promising CIL in PSCs.…”

Efficient Polymer Solar Cells with Alcohol-Soluble Zirconium(IV) Isopropoxide Cathode Buffer Layer

“…Unfortunately, large scale practical application has been inhibited by the poor stability of the devices because the commonly adopted cathode buffer layer (CBL, e.g., calcium (Ca) or barium (Ba)) is prone to oxidative degradation as well as the instable photoactive layer and anode modification layer [9][10][11]. In addition, it is difficult to avoid the interdiffusion of active metal atoms of CBL at the photoactive-layer/metal interface during the thermal evaporation of the CBL, and thus, this leads to an evident performance decrease for PSCs [12] Undoubtedly, the alternative CBL candidates of alkali metal compounds (such as LiF, CsF and Cs 2 CO 3 ) suffer from both of the vacuum involved deposition techniques, which are incompatible with all solution processed PSCs [13,14]. Therefore, considerable efforts have been directed to exploring a stable and solution-processable CBL between an active layer and a cathode since interfacial engineering is a critical factor for the stability improvement of PSCs [15].…”

Theoretical Approach Towards Rational Design and Characterization of Benzo[1,2-b:5-B’]dithiophene (BDT)-Based (A-D-A) Small Molecules of Relevance for High Performance Solar Cells

“…Great progress has been achieved in both donor and acceptor materials development and device optimization, witnessed by the dramatic increase in devices PCEs from less than 2% before 2008 to over than 10% in recent years [11][12][13][14][15]. In this regard, fullerene and their derivatives have been extensively used as acceptor materials within BHJ devices because of their important electronic properties such as small reorganization energy, high electron mobility and affinity [16][17][18].…”