{"id":1122,"date":"2013-07-25T18:26:15","date_gmt":"2013-07-25T18:26:15","guid":{"rendered":"https:\/\/mtlsites.mit.edu\/annual_reports\/2013\/?p=1122"},"modified":"2013-10-07T15:09:44","modified_gmt":"2013-10-07T15:09:44","slug":"recombination-dynamics-of-charge-carriers-in-nanostructured-solar-cells","status":"publish","type":"post","link":"https:\/\/mtlsites.mit.edu\/annual_reports\/2013\/recombination-dynamics-of-charge-carriers-in-nanostructured-solar-cells\/","title":{"rendered":"Recombination Dynamics of Charge Carriers in Nanostructured Solar Cells"},"content":{"rendered":"

Nanostructured solar cells attract increasing attention as a promising photovoltaic (PV) technology[1<\/a>]<\/sup>. Generation of free charge carriers in nanostructured PV devices occurs at the electron donor-acceptor interface, analogous to a pn-junction interface in traditional crystalline Si solar cells. Recombination at this interface constitutes a major pathway of charge carrier loss. Characterizing and controlling recombination dynamics are key to informing design of novel device architectures. Recombination parameters also enable comparisons between different device architectures.<\/p>\n

This work uses the transient optoelectroic techniques[2<\/a>]<\/sup> to probe recombination mechanisms under standard operating conditions in four solar cells. Figure 1 shows the cells: a lead sulfide quantum dot and zinc oxide (QD PbS:ZnO) pn-heterojunction, a chloroaluminium phthalocyanine and fullerene (ClAlPc:C60<\/sub>) planar heterojunction, a tetraphenyldibenzoperiflanthene and C60 <\/sub>(DBP:C60<\/sub>) planar heterojunction, and a DBP and C60<\/sub> planar mixed heterojunction (DBP:( DBP\/C60<\/sub>):C60<\/sub>). Figure\u00a02a shows charge carrier lifetimes as functions of the open-circuit voltage. Varied carrier lifetimes may arise from interface morphologies: e.g.,, the slower recombination transients observed in the DBP:C60<\/sub> devices may be due to their intrinsic planarity. We measure charge carrier density as a function of the open circuit voltage, as in Figure 2b.\u00a0 Combining carrier lifetime and charge carrier density allows us to calculate recombination rates and assign the major recombination to a dominant mechanism. In all devices, the relevant recombination is a geminate recombination of excitons or standard SRH recombination (PbS:ZnO solar cells) and a non-geminate recombination between two free charges. Investigating the type of recombination is critical for designing solar cells with improved efficiency.<\/p>\n

\"Figure<\/a>

Figure 1: Schematics of nanostructured PV architectures studied in this work. Left to right: QD PbS:ZnO pn-heterojunction (inset shows cartoon of QD passivated by organic ligand on ZnO), ClAlPc:C60 planar heterojunction with ClAlPc molecular structure, DBP:C60 planar heterojunction with DBP molecular structure, and DBP:( DBP\/C60):C60 planar mixed heterojunction. All devices are sandwiched between an electron and hole transporting layer such as bathocuproine and molybdenum oxide and ITO and Au as electrodes.<\/p><\/div>\n

\"Figure<\/a>

Figure 2: a) Charge carrier lifetime and b) charge carrier density as function of open circuit voltage for ClAlPc:C60, DBP:C60, (DBP:( DBP\/C60):C60), and PbS:ZnO.<\/p><\/div>\n

 <\/p>\n

  1. Anonymous, \u201cA sunny outlook,\u201d Nature Photonics<\/i>, vol. 6, no. 3, p. 129, Mar. 2012. [↩<\/a>]<\/li>
  2. C. G. Shuttle, B. O\u2019Regan, A. M. Ballantyne, J. Nelson, D. D. C. Bradley, J. de Mello, and J. R. Durrant, \u201cExperimental determination of the rate law for charge carrier decay in a polythiophene: Fullerene solar cell,\u201d Applied Physics Letters<\/i>, vol. 92, p. 3, 2008. [↩<\/a>]<\/li><\/ol>","protected":false},"excerpt":{"rendered":"

    Nanostructured solar cells attract increasing attention as a promising photovoltaic (PV) technology[1]. Generation of free charge carriers in nanostructured PV…<\/p>\n","protected":false},"author":370,"featured_media":1123,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[28,6,8,6083],"tags":[11493,6131],"_links":{"self":[{"href":"https:\/\/mtlsites.mit.edu\/annual_reports\/2013\/wp-json\/wp\/v2\/posts\/1122"}],"collection":[{"href":"https:\/\/mtlsites.mit.edu\/annual_reports\/2013\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/mtlsites.mit.edu\/annual_reports\/2013\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/mtlsites.mit.edu\/annual_reports\/2013\/wp-json\/wp\/v2\/users\/370"}],"replies":[{"embeddable":true,"href":"https:\/\/mtlsites.mit.edu\/annual_reports\/2013\/wp-json\/wp\/v2\/comments?post=1122"}],"version-history":[{"count":10,"href":"https:\/\/mtlsites.mit.edu\/annual_reports\/2013\/wp-json\/wp\/v2\/posts\/1122\/revisions"}],"predecessor-version":[{"id":2547,"href":"https:\/\/mtlsites.mit.edu\/annual_reports\/2013\/wp-json\/wp\/v2\/posts\/1122\/revisions\/2547"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/mtlsites.mit.edu\/annual_reports\/2013\/wp-json\/wp\/v2\/media\/1123"}],"wp:attachment":[{"href":"https:\/\/mtlsites.mit.edu\/annual_reports\/2013\/wp-json\/wp\/v2\/media?parent=1122"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/mtlsites.mit.edu\/annual_reports\/2013\/wp-json\/wp\/v2\/categories?post=1122"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/mtlsites.mit.edu\/annual_reports\/2013\/wp-json\/wp\/v2\/tags?post=1122"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}