Accurate Characterization of Triple‐Junction Polymer Solar Cells

Abstract

organic semiconductors have been developed to absorb light into the near infrared region. [8] The gain in spectral coverage and short-circuit current density (J SC ) in the cells is, however, counteracted by an unavoidable loss in the open-circuit voltage (V OC ) when the bandgap decreases. [9] Given the intrinsic limits of singlejunction organic solar cells, there has been an increasing interest to develop multijunction architectures. [10] This paves the way to efficient solar cells by an improved utilization of photon energy. In a multijunction solar cell sunlight is spectrally distributed over two, or more subcells such that highenergy photons are absorbed in a wide bandgap subcell and low-energy photons in a small bandgap subcell. This reduces the thermalization losses for high-energy photons and the transmission losses for the low-energy photons. Most studies have focused on the tandem architecture, in which identical or different absorber layers are used, resulting in maximum efficiencies in the range of 10-13%. [11][12][13][14][15][16][17][18][19][20][21][22] At least conceptually, stacking three absorber layers in a triple-junction solar cell can lead to a further increase in efficiency. There are few examples of triple-junction organic solar cells. [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] The gain in efficiency achieved by these triple-junction devices was not always accompanied by a critical analysis of the measured performance. In a recent publication, Timmreck et al. methodically analyzed the literature on tandem organic solar cells, shedding light on the fact that the vast majority of the publications on organic tandem cells lacked a proper characterization. [42] Although the paper focused attention on the tandem structure, the argumentations provided can reasonably be extended to the case of triple-junctions. At present, the characterization of organic triple-junctions is often limited to measuring the J−V characteristics under simulated solar radiation and determining the external quantum efficiency (EQE) using different light sources to optically bias the subcells. [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] Nevertheless, organic materials commonly employed for solar cells feature peculiar characteristics that necessitate special attention for their EQE measurement. [42][43][44] An accurate analysis of the effect of bias light and bias voltage on the EQE of triple-junction organic solar cells is necessary.Detailed protocols for the characterization of triple-junction solar cells are available in the literature. [45] For many inorganic triple-junction solar cells the effect of bias voltage on the spectral response is very small, which makes correction for bias voltage not critical. [45] The aim of this work is to provide a characterization protocol for organic triple-junction solar cells that take into account the uniqueness of these particular materials. In order to do so, we combine optical and electrical modeling, use

Solution‐Processed Tin Oxide‐PEDOT:PSS Interconnecting Layers for Efficient Inverted and Conventional Tandem Polymer Solar Cells

“…Therefore, the data series of the representative conventional cell of J71:ITIC was approximated with the dataset of the inverted representative cell, reported in Table S2, Supporting Information. The performance of the PMDPP3T:PC 60 BM series in the inverted configuration was taken from one of our previous work, where we utilized zinc oxide instead of tin oxide (Table S3, Supporting Information) . We then calculated the spectrally resolved fraction of absorbed photons from the subcells and we scaled this by the corresponding IQE (reported in Table S1–S3, Supporting Information).…”

A Universal Route to Fabricate n‐i‐p Multi‐Junction Polymer Solar Cells via Solution Processing

“…The last step is re‐iterated for all thickness combinations of interest. All the relevant data are shown in Table S2 and Figure S3, Supporting Information or are available in the literature . In the optimization, the thickness of the D‐PEDOT:PSS (30 nm) and ZnO (20 nm) in the interconnection layer was kept constant.…”

“…The EQE of the triple junction cell was measured using appropriate light bias, voltage bias, and light intensity corrections following the protocol described in detail recently . From the EQE spectra in Figure a, it can be seen that the BHJ4 middle cell (PDPPTPT:PC 60 BM) gave a low EQE signal, limiting the total current extracted from the device.…”

“…PTB7‐Th:PC 70 BM (BHJ5) has opto‐electronic properties close to PDPPTPT:PC 60 BM (BHJ4) but has a significantly higher IQE of 0.82 (at 145 nm), opening up the possibility of a higher current in a triple‐junction solar cell. We optimized the triple device with BHJ3, BHJ5, and BHJ8 as front, middle, and back subcells using the semi‐empirical method described above . The optimal thicknesses found were 130, 140, and 90 nm for the front, middle, and back subcells, respectively.…”

“…The combination of this data with the normalized J–V characteristics of the subcells returned the J–V characteristics of the triple for each of the tested combination of thicknesses. The determination of the voltage bias correction for the EQE of the two optimized triples followed the reported procedure …”